Description
The present application is concerned with audio splicing.
Coded audio usually comes in chunks of samples, often 1024, 2048 or 4096 samples in
number per chunk. Such chunks are called frames in the following. In the context of
MPEG audio codecs like AAC or MPEG-H 3D Audio, these chunks/frames are called
granules, the encoded chunks/frames are called access units (AU) and the decoded
chunks are called composition units (CU). In transport systems the audio signal is only
accessible and addressable in granularity of these coded chunks (access units). It would
be favorable, however, to be able to address the audio data at some final granularity,
especially for purposes like stream splicing or changes of the configuration of the coded
audio data, synchronous and aligned to another stream such as a video stream, for
example.
What is known so far is the discarding of some samples of a coding unit. The MPEG-4 file
format, for example, has so-called edit lists that can be used for the purpose of discarding
audio samples at the beginning and the end of a coded audio file/bitstream [3].
Disadvantageously, this edit list method works only with the MPEG-4 file format, i.e. is file
format specific and does not work with stream formats like MPEG-2 transport streams.
Beyond that, edit lists are deeply embedded in the MPEG-4 file format and accordingly
cannot be easily modified on the fly by stream splicing devices. In AAC [1], truncation
information may be inserted into the data stream in the form of extension_payload. Such
extension_payload in a coded AAC access unit is, however, disadvantageous in that the
truncation information is deeply embedded in the AAC AU and cannot be easily modified
on the fly by stream splicing devices.
Accordingly, it is an object of the present invention to provide a concept for audio splicing
which is more efficient in terms of, for example, procedural complexity of the splicing
process at stream splicers, and/or audio decoders.
This object is achieved by the subject matter of the independent claims attached herewith.
The invention of the present application is inspired by the idea that audio splicing may be
rendered more effectively by the use of one or more truncation unit packets inserted into
the audio data stream so as to indicate to an audio decoder, for a predetermined access
unit, an end portion of an audio frame with which the predetermined access unit is
associated, as to be discarded in playout.
In accordance with an aspect of the present application, an audio data stream is initially
provided with such a truncation unit packet in order to render the thus provided audio data
stream more easily spliceable at the predetermined access unit at a temporal granularity
finer than the audio frame length. The one or more truncation unit packets are, thus,
addressed to audio decoder and stream splicer, respectively. In accordance with
embodiments, a stream splicer simply searches for such a truncation unit packet in order
to locate a possible splice point. The stream splicer sets the truncation unit packet
accordingly so as to indicate an end portion of the audio frame with which the
predetermined access unit is associated, to be discarded in playout, cuts the first audio
data stream at the predetermined access unit and splices the audio data stream with
another audio data stream so as to abut each other at the predetermined access unit. As
the truncation unit packet is already provided within the spliceable audio data stream, no
additional data is to be inserted by the splicing process and accordingly, bitrate
consumption remains unchanged insofar.
Alternatively, a truncation unit packet may be inserted at the time of splicing. Irrespective
of initially providing an audio data stream with a truncation unit packet or providing the
same with a truncation unit packet at the time of splicing, a spliced audio data stream has
such truncation unit packet inserted thereinto with the end portion being a trailing end
portion in case of the predetermined access unit being part of the audio data stream
leading the splice point and a leading end portion in case of the predetermined access
unit being part of the audio data stream succeeding the splice point.
Advantageous aspects of implementations of the present application are the subject of the
dependent claims. In particular, preferred embodiments of the present application are
described below with respect to the figures, among which:
Fig. 1 schematically shows from top to bottom an audio signal, the audio data
stream having the audio signal encoded thereinto in units of audio frames
of the audio signal, a video consisting of a sequence of frames and another
audio data stream and its audio signal encoded thereinto which are to
potentially replace the initial audio signal from a certain video frame
onwards;
Fig. 2 shows a schematic diagram of a spliceable audio data stream, i.e. an audio
data stream provided with TU packets in order to alleviate splicing actions,
in accordance with an embodiment of the present application;
Fig. 3 shows a schematic diagram illustrating a TU packet in accordance with an
embodiment;
Fig. 4 schematically shows a TU packet in accordance with an alternative
embodiment according to which the TU packet is able to signal a leading
end portion and a trailing end portion, respectively;
Fig. 5 shows a block diagram of an audio encoder in accordance with an
embodiment;
Fig. 6 shows a schematic diagram illustrating a trigger source for splice-in and
splice-out time instants in accordance with an embodiment where same
depend on a video frame raster;
Fig. 7 shows a schematic block diagram of a stream splicer in accordance with an
embodiment with the figure additionally showing the stream splicer as
receiving the audio data stream of Fig. 2 and outputting a spliced audio
data stream based thereon;
Fig. 8 shows a flow diagram of the mode of operation of the stream splicer of Fig.
7 in splicing the lower audio data stream into the upper one in accordance
with an embodiment;
Fig. 9 shows a flow diagram of the mode of operation of the stream splicer in
splicing from the lower audio data stream back to the upper one in
accordance with an embodiment;
Fig. 10 shows a block diagram of an audio decoder according to an embodiment
with additionally illustrating the audio decoder as receiving the spliced
audio data stream shown in Fig. 7 ;
Fig. 11 shows a flow diagram of a mode of operation of the audio decoder of Fig.
10 in order to illustrate the different handlings of access units depending on
the same being IPF access units and/or access units comprising TU
packets;
Fig. 12 shows an example of a syntax of TU packet;
Figs. 13A-C show different examples of how to splice from one audio data stream to the
other, with the splicing time instant being determined by a video, here a
video at 50 frames per second and an audio signal coded into the audio
data streams at 48 kHz with 1024 sample-wide granules or audio frames
and with a timestamp timebase of 90 kHz so that one video frame duration
equals 1800 timebase ticks while one audio frame or audio granule equals
1920 timebase ticks;
Fig. 14 shows a schematic diagram illustrating another exemplary case of splicing
two audio data streams at a splicing time instant determined by an audio
frame raster using the exemplary frame and sample rates of Figs. 13A-C;
Fig. 15 shows a schematic diagram illustrating an encoder action in splicing two
audio data streams of different coding configurations in accordance with an
embodiment;
Fig. 16 shows different cases of using splicing in accordance with an embodiment;
and
Fig. 17 shows a block diagram of an audio encoder supporting different coding
configurations in accordance with an embodiment.
Fig. 1 shows an exemplary portion out of an audio data stream in order to illustrate the
problems occurring when trying to splice the respective audio data stream with another
audio data stream. Insofar, the audio data stream of Fig. 1 forms a kind of basis of the
T EP2015/070493
audio data streams shown in the subsequent figures. Accordingly, the description brought
forward with the audio data stream of Fig. 1 is also valid for the audio data streams
described further beiow.
The audio data stream of Fig. 1 is generally indicated using reference sign 10. The audio
data stream has encoded there into an audio signal 12. In particular, the audio signal 12 is
encoded into audio data stream in units of audio frames 14, i.e. temporal portions of the
audio signal 12 which may, as illustrated in Fig. 1, be non-overlapping and abut each
other temporally, or alternatively overlap each other. The way the audio signal 12 is, in
units of the audio frames 14, encoded audio data stream 10 may be chosen differently:
transform coding may be used in order to encode the audio signal in the units of the audio
frames 14 into data stream 10. In that case, one or several spectral decomposition
transformations may be applied onto the audio signal of audio frame 14, with one or more
spectral decomposition transforms temporally covering the audio frame 14 and extending
beyond its leading and trailing end. The spectral decomposition transform coefficients are
contained within the data stream so that the decoder is able to reconstruct the respective
frame by way of inverse transformation. The mutually and even beyond audio frame
boundaries overlapping transform portions in units of which the audio signal is spectrally
decomposed are windowed with so called window functions at encoder and/or decoder
side so that a so-called overlap-add process at the decoder side according to which the
inversely transformed signaled spectral composition transforms are overlapped with each
other and added, reveals the reconstruction of the audio signal 12.
Alternatively, for example, the audio data stream 10 has audio signal 12 encoded
thereinto in units of the audio frames 14 using linear prediction, according to which the
audio frames are coded using linear prediction coefficients and the coded representation
of the prediction residual using, in turn, long term prediction (LTP) coefficients like LTP
gain and LTP lag, codebook indices and/or a transform coding of the excitation (residual
signal). Even here, the reconstruction of an audio frame 14 at the decoding side may
depend on a coding of a preceding frame or into, for example, temporal predictions from
one audio frame to another or the overlap of transform windows for transform coding the
excitation signal or the like. The circumstance is mentioned here, because it plays a role
in the following description.
For transmission and network handling purposes, the audio data stream 10 is composed
of a sequence of payload packets 16. Each of the payload packets 16 belongs to a
respective one of the sequence of access units 18 into which the audio data stream 0 is
partitioned along stream order 20. Each of the access units 18 is associated with a
respective one of the audio frames 14 as indicated by doubie-headed arrows 22 in Fig. 1.
As illustrated in Fig. 1, the temporal order of the audio frames 14 may coincide with the
order of the associated audio frames 18 in data stream 10: an audio frame 14 immediately
succeeding another frame may be associated with an access unit in data stream 10
immediately succeeding the access unit of the other audio frame in data stream 10.
That is, as depicted in Fig. 1, each access unit 18 may have one or more payload packets
16. The one or more payload packets 16 of a certain access unit 18 has/have encoded
thereinto the aforementioned coding parameters describing the associated frame 14 such
as spectral decomposition transform coefficients, LPCs, and/or a coding of the excitation
signal.
The audio data stream 10 may also comprise timestamp information 24 which indicates
for each access unit 18 of the data stream 10 this timestamp t , at which the audio frame i
with which the respective access unit 18 AU, is associated, is to be played out. The
timestamp information 24 may, as illustrated in Fig. 1, be inserted into one of the one or
more packets 16 of each access unit 18 so as to indicate the timestamp of the associated
audio frame, but different solutions are feasible as well, such as the insertion of the
timestamp information t of an audio frame i into each of the one or more packets of the
associated access unit AU,.
Owing to the packetization, the access unit partitioning and the timestamp information 24,
the audio data stream 10 is especially suitable for being streamed between encoder and
decoder. That is, the audio data stream 10 of Fig. 1 is an audio data stream of the stream
format. The audio data stream of Fig. 1 may, for instance, be an audio data stream
according to MPEG-H 3D Audio or MHAS [2].
In order to ease the transport/network handling, packets 16 may have byte-aligned sizes
and packets 16 of different types may be distinguished. For example, some packets 16
may relate to a first audio channel or a first set of audio channels and have a first packet
type associated therewith, while packets having another packet type associated therewith
have encoded thereinto another audio channel or another set of audio channels of audio
signal 12 encoded thereinto. Even further packets may be of a packet type carrying
seldom changing data such as configuration data, coding parameters being valid, or being
used by, sequence of access units. Even other packets 16 may be of a packet type
carrying coding parameters valid for the access unit to which they belong, while other
payioad packets carry codings of samples vaiues, transform coefficients, LFC coefficients,
or the like. Accordingly, each packet 16 may have a packet type indicator therein which is
easily accessible by intermediate network entities and the decoder, respectively. The TU
packets described hereinafter may be distinguishable from the payload packets by packet
type.
As long as the audio data stream 10 is transmitted as it is, no problem occurs. However,
imagine that the audio signal 12 is to be played out at decoding side until some point in
time exemplarily indicated by t in Fig. 1, only. Fig. 1 illustrates, for example, that this point
in time t may be determined by some external clock such as a video frame clock. Fig. 1,
for instance, illustrates at 26 a video composed of a sequence of frames 28 in a timealigned
manner with respect to the audio signal 12, one above the other. For instance, the
timestamp T ame could be the timestamp of the first picture of a new scene, new program
or the like, and accordingly it could be desired that the audio signal 2 is cut at that time t
= Tframe and replaced by another audio signal 12 from that time onwards, representing, for
instance, the tone signal of the new scene or program. Fig. 1, for instance, illustrates an
already existing audio data stream 30 constructed in the same manner as audio data
stream 10, i.e. using access units 18 composed of one or more payload packets 16 into
which the audio signal 32 accompanying or describing the sequence of pictures of frames
28 starting at timestamp Tframe in audio frames 14 in such a manner that the first audio
frame 14 has its leading end coinciding with time timestamp Tframe , i.e. the audio signal 32
is to be played out with the leading end of frame 14 registered to the playout of timestamp
T f m .
Disadvantageously, however, the frame rate of frames 14 of audio data stream 0 is
completely independent from the frame rate of video 26. It is accordingly completely
random where within a certain frame 14 of the audio signal 12 t = Tframe falls into. That is,
without any additional measure, it would merely be possible to completely leave off
access unit AUj associated with the audio frame 14, j , within which t lies, and appending
at the predecessor access unit AI of audio data stream 0 the sequence of access units
18 of audio data stream 30, thereby however causing a mute in the leading end portion 34
of audio frame j of audio signal 12 .
The various embodiments described hereinafter overcome the deficiency outlined above
and enable a handling of such splicing problems.
Fig. 2 shows an audio data stream in accordance with an embodiment of the present
application. The audio data stream of Fig. 2 is generally indicated using reference sign 40.
Primarily, the construction of the audio signal 40 coincides with the one explained above
with respect to the audio data stream 10, i.e. the audio data stream 40 comprises a
sequence of payload packets, namely one or more for each access unit 8 into which the
data stream 40 is partitioned. Each access unit 18 is associated with a certain one of the
audio frames of the audio signal which is encoded into data stream 40 in the units of the
audio frames 14. Beyond this, however, the audio data stream 40 has been "prepared" for
being spliced within an audio frame with which any predetermined access unit is
associated. Here, this is exemplarily access unit AU, and access unit AUj . Let us refer to
access unit AU, first. In particular, the audio data stream 40 is rendered "spliceable" by
having a truncation unit packet 42 inserted thereinto, the truncation unit packet 42 being
settable so as to indicate, for access unit AU,, an end portion of the associated audio
frame i as to be discarded out in playout. The advantages and effects of the truncation
unit packet 42 will be discussed hereinafter. Some preliminary notes, however, shall be
made with respect to the positioning of the truncation unit packet 42 and the content
thereof. For example, although Fig. 2 shows truncation unit packet 42 as being positioned
within the access unit AU i.e. the one the end portion of which truncation unit packet 42
indicates, truncation unit packet 42 may alternatively be positioned in any access unit
preceding access unit AU,. Likewise, even if the truncation unit packet 42 is within access
unit AU,, access unit 42 is not required to be the first packet in the respective access unit
AU, as exemplarily illustrated Fig. 2 .
In accordance with an embodiment which is illustrated in Fig. 3 , the end portion indicated
by truncation unit packet 42 is a trailing end portion 44, i.e. a portion of frame 14
extending from some time instant tjnner within the audio frame 14 to the trailing end of
frame 14. In other words, in accordance with the embodiment of Fig. 3 , there is no syntax
element signaling whether the end portion indicated by truncation unit packet 42 shall be a
leading end portion or a trailing end portion. However, the truncation unit packet 42 of Fig.
3 comprises a packet type index 46 indicating that the packet 42 is a truncation unit
packet, and a truncation length element 48 indicating a truncation length, i.e. the temporal
length At of trailing end portion 44. The truncation length 48 may measure the length of
portion 44 in units of individual audio samples, or in n-tuples of consecutive audio samples
with n being greater than one and being, for example, smaller than N samples with N
being the number of samples in frame 14.
It will be described later that the truncation unit packet 42 may optionally comprise one or
more flags 50 and 52. For example, flag 50 could be a splice-out flag indicating that the
access unit AU, for which the truncation unit packet 42 indicates the end portion 44, is
prepared to be used as a splice-out point. Flag 52 could be a flag dedicated to the
decoder for indicating whether the current access unit AUi has actually been used as a
splice-out point or not. However, flags 50 and 52 are, as just outlined, merely optional. For
example, the presence of TU packet 42 itself could be a signal to stream splicers and
decoders that the access unit to which the truncation unit 42 belongs is such a access unit
suitable for splice-out, and a setting of truncation length 48 to zero could be an indication
to the decoder that no truncation is to be performed and no splice-out, accordingly.
The notes above with respect to TU packet 42 are valid for any TU packet such as TU
packet 58.
As will be described further below, the indication of a leading end portion of an access unit
may be needed as well. In that case, a truncation unit packet such as TU packet 58, may
be settable so as to indicate a trailing end portion as the one depicted in Fig. 3 . Such a TU
packet 58 could be distinguished from leading end portion truncation unit packets such as
42 by means of the truncation unit packet's type index 46. In other words, different packet
types could be associated with TU packets 42 indicating trailing end portions and TU
packets being for indicating leading end portions, respectively.
For the sake of completeness, Fig. 4 illustrates a possibility according to which truncation
unit packet 42 comprises, in addition to the syntax elements shown in Fig. 3 , a
leading/trailing indicator 54 indicating whether the truncation length 48 is measured from
the leading end or the trailing end of audio frame i towards the inner of audio frame i , i.e.
whether the end portion, the length of which is indicated by truncation length 48 is a
trailing end portion 44 or a leading end portion 56. The TU packets' packet type would be
the same then.
As will be outlined in more detail below, the truncation unit packet 42 renders access unit
AU, suitable for a splice-out since it is feasible for stream splicers described further below
to set the trailing end portion 44 such that from the externally defined splice-out time t
(compare Fig. 1) on, the playout of the audio frame i is stopped. From that time on, the
audio frames of the spliced-in audio data stream may be played out.
However, Fig. 2 also illustrates a further truncation unit packet 58 as being inserted into
the audio data stream 40, this further truncation unit packet 58 being settable so as to
indicate for access unit AUj , with j > i , that an end portion thereof is to be discarded in
playout. This time, however, the access unit AUj , i.e. access unit AUj+ , has encoded
thereinto its associated audio frame j in a manner independent from the immediate
predecessor access unit Au , namely in that no prediction references or internal decoder
registers are to be set dependent on the predecessor access unit AU^, or in that no
overlap-add process renders a reconstruction of the access unit A ) a requirement for
correctly reconstructing and playing-out access unit AUj . In order to distinguish access unit
AUj , which is an immediate playout access unit, from the other access units which suffer
from the above-outlined access unit interdependencies such as, inter alias, AU access
unit AUj is highlighted using hatching.
Fig. 2 illustrates the fact that the other access units shown in Fig. 2 have their associated
audio frame encoded thereinto in a manner so that their reconstruction is dependent on
the immediate predecessor access unit in the sense that correct reconstruction and
playout of the respective audio frame on the basis of the associated access unit is merely
feasible in the case of having access to the immediate predecessor access unit, as
illustrated by small arrows 60 pointing from predecessor access unit to the respective
access unit. In the case of access unit AUj , the arrow pointing from the immediate
predecessor access unit, namely AUj i, to access unit AUj is crossed-out in order to
indicate the immediate-playout capability of access unit AUj . For example, in order to
provide for this immediate playout capability, access unit AUj has additional data encoded
therein, such as initialization information for initializing internal registers of the decoder,
data allowing for an estimation of aliasing cancelation information usually provided by the
temporally overlapping portion of the inverse transforms of the immediate predecessor
access unit or the like.
The capabilities of access units AU, and AUj are different from each other: access unit AU,
is, as outlined below, suitable as a splice-out point owing to the presence of the truncation
unit packet 42. In other words, a stream splicer is able to cut the audio data stream 40 at
access unit AUi so as to append access units from another audio data stream, i.e. a
spliced-in audio data stream.
This is feasible at access unit AUj as well, provided that TU packet 58 is capable of
indicating a trailing end portion 44. Additionally or alternatively, truncation unit packet 58 is
settable to indicate a leading end portion, and in that case access unit AUj is suitable to
serve as a splice-(back-)in occasion. That is, truncation unit packet 58 may indicate a
leading end portion of audio frame j not to be played out and until that point in time, i.e.
until the trailing end of this trailing end portion, the audio signal of the (preliminarily)
spliced-in audio data stream may be played-out.
For example, the truncation unit packet 42 may have set splice-out flag 50 to zero, while
the splice-out flag 50 of truncation unit packet 58 may be set to zero or may be set to 1.
Some explicit examples will be described further below such as with respect to Fig. 16.
It should be noted that there is no need for the existence of a splice-in capable access unit
AUj . For example, the audio data stream to be spliced-in could be intended to replace the
play-out of audio data stream 40 completely from time instant t onwards, i.e. with no
splice-(back-)in taking place to audio data stream 40. However, if the audio data stream to
be spliced-in is to replace the audio data stream's 40 audio signal merely preliminarily,
then a splice-in back to the audio data stream 40 is necessary, and in that case, for any
splice-out TU packet 42 there should be a splice-in TU packet 58 which follows in data
stream order 20.
Fig. 5 shows an audio encoder 70 for generating the audio data stream 40 of Fig. 2 . The
audio encoder 70 comprises an audio encoding core 72 and a truncation packet inserter
74. The audio encoding core 72 is configured to encode the audio signal 12 which enters
the audio encoding core 72 in units of the audio frames of the audio signal, into the
payload packets of the audio data stream 40 in a manner having been described above
with respect to Fig. 1, for example. That is, the audio encoding core 72 may be a
transform coder encoding the audio signal 12 using a lapped transform, for example, such
as an MDCT, and then coding the transform coefficients, wherein the windows of the
lapped transform may, as described above, cross frame boundaries between consecutive
audio frames, thereby leading to an interdependency of immediately consecutive audio
frames and their associated access units. Alternatively, the audio encoder core 72 may
use linear prediction based coding so as to encode the audio signal 12 into data stream
40. For example, the audio encoding core 72 encodes linear prediction coefficients
describing the spectral envelope of the audio signal 12 or some pre-filtered version
thereof on an at least frame-by-frame basis, with additionally coding the excitation signal.
Continuous updates of predictive coding or lapped transform issues concerning the
excitation signal coding may lead to the interdependencies between immediately
consecutive audio frames and their associated access units. Other coding principles are,
however, imaginable as well.
The truncation unit packet inserter 74 inserts into the audio data stream 40 the truncation
unit packets such as 42 and 58 in Fig. 2 . As shown in Fig. 5 , TU packet inserter 74 may,
to this end, be responsive to a splice position trigger 76. For example, the splice position
trigger 76 may be informed of scene or program changes or other changes in a video, i.e.
within the sequence of frames, and may accordingly signal to the truncation unit packet
inserter 74 any first frame of such new scene or program. The audio signal 12, for
example, continuously represents the audio accompaniment of the video for the case that,
for example, none of the individual scenes or programs in the video are replaced by other
frame sequences or the like. For example, imagine that a video represents a live soccer
game and that the audio signal 12 is the tone signal related thereto. Then, splice position
trigger 76 may be operated manually or automatically so as to identify temporal portions of
the soccer game video which are subject to potential replacement by ads, i.e. ad videos,
and accordingly, trigger 76 would signal beginnings of such portions to TU packet inserter
74 so that the latter may, responsive thereto, insert a TU packet 42 at such a position,
namely relating to the access unit associated with the audio frame within which the first
video frame of the potentially to be replaced portion of the video starts, lies. Further,
trigger 76 informs the TU packet inserter 74 on the trailing end of such potentially to be
replaced portions, so as to insert a TU packet 58 at a respective access unit associated
with an audio frame into which the end of such a portion falls. As far as such TU packets
58 are concerned, the audio encoding core 72 is also responsive to trigger 76 so as to
differently or exceptionally encode the respective audio frame into such an access unit AUj
(compare Fig. 2) in a manner allowing immediately playout as described above. In
between, i.e. within such potentially to be replaced portions of the video, trigger 76 may
intermittently insert TU packets 58 in order to serve as a splice-in point or splice-out point.
In accordance with a concrete example, trigger 76 informs, for example, the audio
encoder 70 of the timestamps of the first or starting frame of such a portion to be
potentially replaced, and the timestamp of the last or end frame of such a portion, wherein
the encoder 70 identifies the audio frames and associated access units with respect to
which TU packet insertion and, potentially, immediate playout encoding shall take place
by identifying those audio frames into which the timestamps received from trigger 76 fall.
In order to illustrate this, reference is made to Fig. 6 which shows the fixed frame raster at
which audio encoding core 72 works, namely at 80, aiong with the fixed frame raster 82 of
a video to which the audio signal 12 belongs. A portion 84 out of video 86 is indicated
using a curly bracket. This portion 84 is for example manually determined by an operator
or fully or partially automatically by means of scene detection. The first and the last frames
88 and 90 have associated therewith timestamps T and Te, which lie within audio frames i
and j of the frame raster 80. Accordingly, these audio frames 14, i.e. i and j , are provided
with TU packets by TU packet inserter 74, wherein audio encoding core 72 uses
immediate playout mode in order to generate the access unit corresponding to audio
frame j .
It should be noted that the TU packet inserter 74 may be configured to insert the TU
packets 42 and 58 with default values. For example, the truncation length syntax element
48 may be set to zero. As far as the splice-in flag 50 is concerned, which is optional, same
is set by TU packet inserter 74 in the manner outlined above with respect to Figs. 2 to 4 ,
namely indicating splice-out possibility for TU packets 42 and for all TU packets 58
besides those registered with the final frame or image of video 86. The splice-active flag
52 would be set to zero since no splice has been applied so far.
It is noted with respect to the audio encoder of Fig. 6 , that the way of controlling the
insertion of TU packets, i.e. the way of selecting the access units for which insertion is
performed, as explained with respect to Figs. 5 and 6 is illustrative only and other ways of
determining those access units for which insertion is performed is feasible as well. For
example, each access unit, every N-th (N>2) access unit or each IPF access unit could
alternatively be provided with a corresponding TU packet.
It has not been explicitly mentioned above, but preferably the TU packets are coded in
uncompressed form so that a bit consumption (coding bitrate) of a respective TU packet is
independent from the TU packet's actual setting. Having said this, it is further worthwhile
to note that the encoder may, optionally, comprise a rate control (not shown in Fig. 5),
configured to log a fill level of a coded audio buffer so as to get sure that a coded audio
buffer at the decoder's side at which the data stream 40 is received neither underflows,
thereby resulting in stalls, nor overflows thereby resulting in loss of packets 12. The
encoder may, for example, control/vary a quantization step size in order to obey the fill
level constraint with optimizing some rate/distortion measure. In particular, the rate control
may estimate the decoder's coded audio buffer's fill level assuming a predetermined
transmission capacity/bitrate which may be constant or quasi constant and, for example,
be preset by an external entity such as a transmission network. The coding rate of the TU
packets of data stream 40 are taken into account by the rate control. Thus, in the form
shown in Fig. 2 , i.e. in the version generated by encoder 70, the data stream 40 keeps the
preset bitrate with varying, however, therearound in order to compensate for the varying
coding complexity if the audio signal 12 in terms of its rate/distortion ratio with neither
overloading the decoder's coded audio fill level (leading to overflow) nor derating the
same (leading to underflow). However, as has already been briefly outlined above, and
will be described in more detail below, every splice-out access unit AU, is, accordance to
preferred embodiments, supposed to contribute to the playout at decoder side merely for
a temporal duration smaller than the temporal length of its audio frame i . As will get clear
from the description brought forward below, the (leading) access unit of a spliced-in audio
data stream spliced with data stream 40 at the respective splice-out AU such as A as a
splice interface, will displace the respective splice-out AU's successor AUs. Thus, from
that time onwards, the bitrate control performed within encoder 70 is obsolete. Beyond
that, said leading AU is preferably coded in a self-contained manner so as to allow
immediate playout, thereby consuming more coded bitrate compared to non-IPF AUs.
Thus, in accordance with an embodiment, the encoder 70 plans or schedules the rate
control such that the logged fill level at the respective splice-out AU's end, i.e. at its border
to the immediate successor AU, assumes, for example, a predetermined value such as for
example, ¼ or a value between ¾ and 1/8 of the maximum fill level. By this measure,
other encoders preparing the audio data streams supposed to be spliced in into data
stream 40 at the splice-out AUs of data stream 40 may rely on the fact that the decoder's
coded audio buffer fill level at the time of starting to receive their own AUs (in the following
sometimes distinguished from the original ones by an apostrophe) is at the predetermined
value so that these other encoders may further develop the rate control accordingly. The
description brought forward so far concentrated on splice-out AUs of data stream 40, but
the adherence to predetermined estimated/logged fill level is may also be achieved by the
rate control for splice-(back)-in AUs such as AUj even if not playing a double role as
splice-in and splice-out point. Thus, said other encoders may, likewise, control their rate
control in such a manner that the estimated or logged fill level assumes a predetermined
fill level at a trailing AU of their data stream's AU sequence. Same may be the same as
the one mentioned for encoder 70 with respect to splice-out AUs. Such trailing AUs may
be supposed to from splice-back AUs supposed to from a splice point with the splice-in
AUs of data stream 40 such as AUj . Thus, if the encoder's 70 rate control has
planned/scheduled the coded bit rate such that the estimated/logged fill level assumes the
predetermined fill level at (or better after) AUj , then this bit rate control remains even valid
in case of splicing having been performed after encoding and outputting data stream 40.
The predetermined fill level just-mentioned could be known to encoders by default, i.e.
agreed therebetween. Alternatively, the respective AU could by provided with an explicit
signaling of that estimated/logged fill level as assumed right after the respective splice-in
or splice-out AU. For example, the value could be transmitted in the TU packet of the
respective splice-in or splice-out AU. This costs additional side information overhead, but
the encoder's rate control could be provided with more freedom in developing the
estimated/logged fill level at the splice-in or splice-out AU: for example, it may suffice then
that the estimated/logged fill level after the respective splice-in or splice-out AU is below
some threshold such as ¾ the maximum fill level, i.e. the maximally guaranteed capacity
of the decoder's coded audio buffer.
With respect to data stream 40, this means that same is rate controlled to vary around a
predetermined mean bitrate, i.e. it has a mean bitrate. The actual bitrate of the splicable
audio data stream varies across the sequence of packets, i.e. temporally. The (current)
deviation from the predetermined mean bitrate may be integrated temporally. This
integrated deviation assumes, at the splice-in and splice-out access units, a value within a
predetermined interval which may be less than 1/ wide than a range (max-min) of the
integrated bitrate deviation, or may assume a fixed value, e.g. a value equal for all splicein
and splice-out AUs, which may be smaller than ¾ of a maximum of the integrated
bitrate deviation. As described above, this value may be pre-set by default. Alternatively,
the value is not fixed and not equal for all splice-in and splice-out AUs, but may by
signaled in the data stream.
Fig. 7 shows a stream splicer for splicing audio data streams in accordance with an
embodiment. The stream splicer is indicated using reference 100 and comprises a first
audio input interface 102, a second audio input interface 104, a splice point setter 106 and
a splice multiplexer 108.
At interface 102, the stream splicer expects to receive a "spliceable" audio data stream,
i.e. an audio data stream provided with one or more TU packets. In Fig. 7 it has been
exemplarily illustrated that audio data stream 40 of Fig. 2 enters stream splicer 100 at
interface 102.
Another audio data stream 110 is expected to be received at interface 104. Depending on
the implementation of the stream splicer 100, the audio data stream 110 entering at
interface 04 may be a "non-prepared" audio data stream such as the one explained and
described with respect to Fig. 1, or a prepared one as it will be illustratively set out below.
The splice point setter 106 is configured to set the truncation unit packet included in the
data stream entering at interface 102, i.e. TU packets 42 and 58 of data stream 40 in the
case of Fig. 7 , and if present the truncation unit packets of the other data stream 110
entering at interface 104, wherein two such TU packets are exemplarily shown in Fig. 7 ,
namely a TU packet 112 in a leading or first access unit AU'i of audio data stream 110,
and a TU packet 114 in a last or trailing access unit AU' K of audio data stream 110. In
particular, the apostrophe is used in Fig. 7 in order to distinguish between access units of
audio data stream 110 from access units of audio data stream 40. Further, in the example
outlined with respect to Fig. 7 , the audio data stream 110 is assumed to be pre-encoded
and of fixed-length, namely here of K access units, corresponding to K audio frames
which together temporally cover a time interval within which the audio signal having been
encoded into data stream 40 is to be replaced. In Fig. 7 , it is exemplarily assumed that
this time interval to be replaced extends from the audio frame corresponding to access
unit AU to the audio frame corresponding to access unit AUj .
In particular, the splice point setter 106 is to, in a manner outlined in more detail below,
configured to set the truncation unit packets so that it becomes clear that a truncation
actually takes place. For example, while the truncation length 48 within the truncation
units of the data streams entering interfaces 102 and 104 may be set to zero, splice point
setter 106 may change the setting of the transform length 48 of the TU packets to a non¬
zero value. How the value is determined is the subject of the explanation brought forward
below.
The splice multiplexer 108 is configured to cut the audio data stream 40 entering at
interface 102 at an access unit with a TU packet such as access unit AU, with TU packet
42, so as to obtain a subsequence of payload packets of this audio data stream 40,
namely here in Fig. 7 exemplarily the subsequence of payload packets corresponding to
access units preceding and including access unit AU,, and then splicing this subsequence
with a sequence of payload packets of the other audio data stream 110 entering at
interface 104 so that same are immediately consecutive with respect to each other and
abut each other at the predetermined access unit. For example, splice multiplexer 108
cuts audio data stream 40 at access unit AU, so as to just include the payload packet
belonging to that access unit All, with then appending the access units AU' of audio data
stream 110 starting with access unit Aϋ so that access units AU, and A' Ί abut each
other. As shown in Fig 7 , splice multiplexer 108 acts similarly in the case of access unit
AUj comprising TU packet 58: this time, splice multiplexer 108 appends data stream 40,
starting with payload packets belonging to access unit AUj, to the end of audio data
stream 110 so that access unit AU' K abuts access unit AUj .
Accordingly, the splice point setter 106 sets the TU packet 42 of access unit AU so as to
indicate that the end portion to be discarded in playout is a trailing end portion since the
audio data stream's 40 audio signal is to be replaced, preliminarily, by the audio signal
encoded into the audio data stream 110 from that time onwards. In case of truncation unit
58, the situation is different: here, splice point setter 106 sets the TU packet 58 so as to
indicate that the end portion to be discarded in playout is a leading end portion of the
audio frame with which access unit AUj is associated. It should be recalled, however, that
the fact that TU packet 42 pertains to a trailing end portion while TU packet 58 relates to a
leading end portion is already derivable from the inbound audio data stream 40 by way of
using, for example, different TU packet identifiers 46 for TU packet 42 on the one hand
and TU packet 58 on the other hand.
The stream splicer 100 outputs the spliced audio data stream thus obtained an output
interface 116, wherein the spliced audio data stream is indicated using reference sign
120.
It should be noted that the order in which splice multiplexer 108 and splice point setter 06
operate on the access units does not need to be as depicted in Fig. 7 . That is, although
Fig. 7 suggests that splice multiplexer 108 has its input connected to interfaces 102 and
104, respectively, with the output thereof being connected to output interface 116 via
splice point setter 106, the order among splice multiplexer 108 and splice point setter 106
may be switched.
In operation, the stream splicer 100 may be configured to inspect the splice-in syntax
element 50 comprised by truncation unit packets 52 and 58 within audio data stream 40
so as to perform the cutting and splicing operation on the condition of whether or not the
splice-in syntax element indicates the respective truncation unit packet as relating to a
splice-in access unit. This means the following: the splice process illustrated so far and
outlined in more detail below may have been triggered by TU packet 42, the splice-in flag
50 is set to one, as described with respect to Fig. 2 . Accordingly, the setting of this flag to
one is detected by stream splicer 100, whereupon the spiice-in operation described in
more detail below, but already outlined above, is performed.
As outlined above, splice point setter 106 may not need to change any settings within the
truncation unit packets as far as the discrimination between splice-in TU packets such as
TU packet 42 and the splice-out TU packets such as TU packets 58 is concerned.
However, the splice point setter 06 sets the temporal length of the respective end portion
to be discarded in playout. To this end, the splice point setter 106 may be configured to
set a temporal length of the end portion to which the TU packets 42, 58, 112 and 114
refer, in accordance with an external clock. This external clock 122 stems, for example,
from a video frame clock. For example, imagine the audio signal encoded into audio data
stream 40 represents a tone signal accompanying a video and that this video is video 86
of Fig. 6 . Imagine further that frame 88 is encountered, i.e. the frame starting a temporal
portion 84 into which an ad is to be inserted. Splice point setter 106 may have already
detected that the corresponding access unit AU, comprises the TU packet 42, but the
external clock 122 informs splice point setter 106 on the exact time T at which the original
tone signal of this video shall end and be replaced by the audio signal encoded into data
stream 10. For example, this splice-point time instant may be the time instant
corresponding to the first picture or frame to be replaced by the ad video which in turn is
accompanied by a tone signal encoded into data stream 110.
In order to illustrate the mode of operation of the stream splicer 100 of Fig. 7 in more
detail, reference is made to Fig. 8 , which shows the sequence of steps performed by
stream splicer 100. The process starts with a weighting loop 130. That is, stream splicer
100, such as splice multiplexer 108 and/or splice point setter 106, checks audio data
stream 40 for a splice-in point, i.e. for an access unit which a truncation unit packet 42
belongs to. In the case of Fig. 7 , access unit i is the first access unit passing check 132
with yes, until then check 132 loops back to itself. As soon as the splice-in point access
unit AU has been detected, the TU packet thereof, i.e. 42, is set so as to register the
splice-in point access unit's trailing end portion (its leading end thereof) with the time
instant derived from the external clock 122. After this setting 134 by splice point setter
106, the splice multiplexer 108 switches to the other data stream, i.e. audio data stream
110, so that after the current splice-in access unit AUi, the access units of data stream 110
are put to output interface 116, rather than the subsequent access units of audio data
stream 40. Assuming that the audio signal which is to replace the audio signal of audio
data stream 40 from the splice-in time instant onward, is coded into audio data stream 10
in a manner so that this audio signal is registered with, i.e. starts right away, with the
beginning of the first audio frame which is associated with a first access unit AU\, the
stream splicer 100 merely adapts the timestamp information comprised by audio data
stream 110 so that a timestamp of the leading frame associated with a first access unit
ALT-,, for example, coincides with the splice-in time instant, i.e. the time instant of AU plus
the temporal length of the audio frame associated with AU, minus the temporal length of
the trailing end portion as set in step 134. That is, after multiplexer switching 136, the
adaptation 138 is a task continuously performed for the access unit AU' of data stream
110. However, during this time the splice-out routine described next is performed as well.
In particular, the splice-out routine performed by stream splicer 100 starts with a waiting
loops according to which the access units of the audio data stream 110 are continuously
checked for same being provided with a TU packet 114 or for being the last access unit of
audio data stream 110. This check 142 is continuously performed for the sequence of
access units AU'. As soon as the splice-out access unit has been encountered, namely
AU'K in the case of Fig. 7 , then splice point setter 106 sets the TU packet 114 of this
splice-out access unit so as to register the trailing end portion to be discarded in playout,
the audio frame corresponding to this access unit AUK with a time instant obtained from
the external clock such as a timestamp of a video frame, namely the first after the ad
which the tone signal coded into audio data stream 10 belongs to. After this setting 144,
the splice multiplexer 108 switches from its input at which data stream 110 is inbound, to
its other input. In particular, the switching 146 is performed in a manner so that in the
spliced audio data stream 120, access unit AUj immediately follows access unit AU' K. In
particular, the access unit AUj is the access unit of data stream 40, the audio frame of
which is temporally distanced from the audio frame associated with the splice-in access
unit AU, by a temporal amount which corresponds to the temporal length of the audio
signal encoded into data stream 110 or deviates therefrom by less than a predetermined
amount such as a length or half a length of the audio frames of the access units of audio
data stream 40.
Thereinafter, splice point setter 106 sets in step 148 the T U packet 58 of access unit AUj
to register the leading end portion thereof to be discarded in playout, with the time instant
with which the trailing end portion of the audio frame of access unit AU' had been
registered in step 144. By this measure, the timestamp of the audio frame of access unit
AUj equals the timestamp of the audio frame of access unit AU' K plus a temporal length of
the audio frame of access unit AU' minus the sum of the trailing end portion of audio
frame of access unit AU' and the leading end portion of the audio frame of access unit
AUj. This fact will become clearer looking at the examples provided further below.
This splice-in routine is also started after the switching 146. Similar to ping-pong, the
stream splicer 100 switches between the continuous audio data stream 40 on the one
hand and audio data streams of predetermined length so as to replace predetermined
portions, namely those between access units with TU packets on the one hand and TU
packets 58 on the other hand, and back again to audio stream 40.
Switching from interface 102 to 104 is performed by the splice-in routine, while the spliceout
routine leads from interface 104 to 102.
It is emphasized, however, again that the example provided with respect to Fig. 7 has
merely been chosen for illustration purposes. That is, the stream splicer 100 of Fig. 7 is
not restricted to "bridge" portions to be replaced from one audio data stream 40 by audio
data streams 110 having encoded thereinto audio signals of appropriate length with the
first access unit having the first audio frame encoded thereinto registered to the beginning
of the audio signal to be inserted into the temporal portion to be replaced. Rather, the
stream splicer may be, for instance, for performing a one-time splice process only.
Moreover, audio data stream 110 is not restricted to have its first audio frame registered
with the beginning of the audio signal to be spliced-in. Rather, the audio data stream 110
itself may stem from some source having its own audio frame clock which runs
independently from the audio frame clock underlying audio data stream 40. In that case,
switching from audio data stream 40 to audio data stream 110 would, in addition to the
steps shown in Fig. 8 , also comprise the setting step corresponding to step 148: the
setting of the TU packet of the audio data stream 110 .
It should be noted that the above description of the stream splicer's operation may be
varied with respect to the timestamp of AUs of the spliced audio data stream 120 for
which a TU packet indicates a leading end portion to be discarded in playout. Instead of
leaving the AU's original timestamp, the stream multiplexer 108 could be configured to
modify the original timestamp thereof by adding the leading end portion's temporal length
to the original timestamp thereby pointing to the trailing end of the leading end portion and
thus, to the time from which on the AU's audio frame fragment is be actually played out.
This alternative is illustrated by the timestamp examples in Fig. 16 discussed later.
Fig. 0 shows an audio decoder 160 in accordance with an embodiment of the present
application. Exemplarily, the audio decoder 160 is shown as receiving the spliced audio
data stream 120 generated by stream splicer 100. However, similar to the statement
made with respect to the stream splicer, the audio decoder 160 of Fig. 10 is not restricted
to receive spliced audio data streams 120 of the sort explained with respect to Figs. 7 to
9 , where one base audio data stream is preliminarily replaced by other audio data streams
having the corresponding audio signal length encoded thereinto.
The audio decoder 160 comprises an audio decoder core 162 which receives the spliced
audio data stream and an audio truncator 164. The audio decoding core 162 performs the
reconstruction of the audio signal in units of audio frames of the audio signal from the
sequence of payload packets of the inbound audio data stream 120, wherein, as
explained above, the payload packets are individually associated with a respective one of
the sequence of access units into which the spliced audio data stream 120 is partitioned.
As each access unit 120 is associated with a respective one of the audio frames, the
audio decoding core 162 outputs the reconstructed audio samples per audio frame and
associated access unit, respectively. As described above, the decoding may involve an
inverse spectral transformation and owing to an overlap/add process or, optionally,
predictive coding concepts, the audio decoding core 162 may reconstruct the audio frame
from a respective access unit while additionally using, i.e. depending on, a predecessor
access unit. However, whenever an immediate playout access unit arrives, such as
access unit AUj , the audio decoding core 162 is able to use additional data in order to
allow for an immediate playout without needing or expecting any data from a previous
access unit. Further, as explained above, the audio decoding core 162 may operate using
linear predictive decoding. That is, the audio decoding core 162 may use linear prediction
coefficients contained in the respective access unit in order to form a synthesis filter and
may decode an excitation signal from the access unit involving, for instance, transform
decoding, i.e. inverse transforming, table lookups using indices contained in the
respective access unit and/or predictive coding or internal state updates with then
subjecting the excitation signal thus obtained to the synthesis filter or, alternatively,
shaping the excitation signal in the spectral domain using a transfer function formed so as
to correspond to the transfer function of the synthesis filter. The audio truncator 164 is
responsive to the truncation unit packets inserted into the audio data stream 120 and
truncates an audio frame associated with a certain access unit having such TU packets so
as to discard the end portion thereof, which is indicated to be discarded in playout of the
TU packet.
Fig. 11 shows a mode of operation of the audio decoder 160 of Fig. 10. Upon detecting
170 a new access unit, the audio decoder checks whether or not this access unit is one
coded using immediate playout mode. If the current access unit is an immediate playout
frame access unit, the audio decoding core 162 treats this access unit as a self-contained
source of information for reconstructing the audio frame associated with this current
access unit. That is, as explained above the audio decoding core 162 may pre-fill internal
registers for reconstructing the audio frame associated with a current access unit on the
basis of the data coded into this access unit. Additionally or alternatively, the audio
decoding core 162 refrains from using prediction from any predecessor access unit as in
the non-IPF mode. Additionally or alternatively, the audio decoding core 162 does not
perform any overlap-add process with any predecessor access unit or its associated
predecessor audio frame for the sake of aliasing cancelation at the temporally leading end
of the audio frame of the current access unit. Rather, for example, the audio decoding
core 162 derives temporal aliasing cancelation information from the current access unit
itself. Thus, if the check 172 reveals that the current access unit is an IPF access unit,
then the IPF decoding mode 174 is performed by the audio decoding core 162, thereby
obtaining the reconstruction of the current audio frame. Alternatively, if check 172 reveals
that the current access unit is not an IPF one, then the audio decoding core 162 applies
as usual non-IPF decoding mode onto the current access unit. That is, internal registers of
the audio decoding core 162 may be adopted as they are after processing the previous
access unit. Alternatively or additionally, an overlap-add process may be used so as to
assist in reconstructing the temporally trailing end of the audio frame of the current access
unit. Alternatively or additionally, prediction from the predecessor access unit may be
used. The non-IPF decoding 176 also ends-up in a reconstruction of the audio frame of
the current access unit. A next check 178 checks whether any truncation is to be
performed. Check 178 is performed by audio truncator 164. In particular, audio truncator
64 checks whether the current access unit has a TU packet and whether the TU packet
indicates an end portion to be discarded in playout. For example, the audio truncator 164
checks whether a TU packet is contained in the data stream for the current access unit
and whether the splice active flag 52 is set and/or whether truncation length 48 is unequal
to zero. If no truncation takes place, the reconstructed audio frame as reconstructed from
any of steps 174 or 176 is played out completely in step 180. However, if truncation is to
be performed, audio truncator 164 performs the truncation and merely the remaining part
is played out in step 82. In the case of the end portion indicated by the TU packet being
a trailing end portion, the remainder of the reconstructed audio frame is piayed out starting
with the timestamp associated with that audio frame. In case of the end portion indicated
to be discarded in piayout by the TU packet being a leading end portion, the remainder of
the audio frame is played-out at the timestamp of this audio frame plus the temporal
length of the leading end portion. That is, the piayout of the remainder of the current audio
frame is deferred by the temporal length of the leading end portion. The process is then
further prosecuted with the next access unit.
See the example in Fig. 10: the audio decoding core 162 performs normal non-IPF
decoding 176 onto access units AU and AU . However, the latter has TU packet 42. This
TU packet 42 indicates a trailing end portion to be discarded in piayout, and accordingly
the audio truncator 164 prevents a trailing end 84 of the audio frame 14 associated with
access unit AU, from being played out, i.e. from participating in forming the output audio
signal 186. Thereinafter, access unit AU'i arrives. Same is an immediate piayout frame
access unit and is treated by audio decoding core 162 in step 174 accordingly. It should
be noted that audio decoding core 162 may, for instance, comprise the ability to open
more than one instantiation of itself. That is, whenever an IPF decoding is performed, this
involves the opening of a further instantiation of the audio decoding core 162. In any case,
as access unit AU'- is an IPF access unit, it does not matter that its audio signal is actually
related to a completely new audio scene compared to its predecessors A U, , and AU,. The
audio decoding core 162 does not care about that. Rather, it takes access unit AU'i as a
self-contained access unit and reconstructs the audio frame therefrom. As the length of
the trailing end portion of the audio frame of the predecessor access unit AU has probably
been set by the stream splicer 00 , the beginning of the audio frame of access unit AU
immediately abuts the trailing end of the remainder of the audio frame of access unit AU,.
That is, they abut at the transition time T somewhere in the middle of the audio frame of
access unit AU,. Upon encountering access unit AU' K, the audio decoding core 162
decodes this access unit in step 176 in order to reveal or reconstruct this audio frame,
whereupon this audio frame is truncated at its trailing end owing to the indication of the
trailing end portion by its TU packet 114. Thus, merely the remainder of the audio frame of
access unit AU' K up to the trailing end portion is played-out. Then, access unit AUj is
decoded by audio decoding core 162 in the IPF decoding 174, i.e. independently from
access unit AU' K in a self-contained manner and the audio frame obtained therefrom is
truncated at its leading end as its truncation unit packet 58 indicates a leading end portion.
The remainders of the audio frames of access units AU' and AUj abut each other at a
transition time instant T2.
The embodiments described above basically use a signaling that describes if and how
many audio samples of a certain audio frame should be discarded after decoding the
associated access unit. The embodiments described above may for instance be applied to
extend an audio codec such as MPEG-H 3D Audio. The MEPG-H 3D Audio standard
defines a self-contained stream format to transform MPEG-H 3D audio data called MHAS
[2]. In line with the embodiments described above, the truncation data of the truncation
unit packets described above could be signaled at the MHAS level. There, it can be easily
detected and can be easily modified on the fly by stream splicing devices such as the
stream splicer 100 of Fig. 7 . Such a new MHAS packet type could be tagged with
PACTYP_CUTRUNCATION, for example. The payload of this packet type could have the
syntax shown in Fig. 12 . In order to ease the concordance between the specific syntax
example of Fig. 12 and the description brought forward above with respect to Figs. 3 and
4 , for example, the reference signs of Figs. 3 and 4 have been reused in order to identify
corresponding syntax elements in Fig. 12. The semantics could be as follows:
isActive: If 1 the truncation message is active, if 0 the decoder should ignore the
message.
canSplice: tells a splicing device that a splice can start or continue here. (Note: This is
basically an ad-begin flag, but the splicing device can reset it to 0 since it does not carry
any information for the decoder.)
truncRight: if 0 truncate samples from the end of the AU, if 1 truncate samples from the
beginning of the AU.
nTruncSamples: number of samples to truncate.
Note that the MHAS stream guarantees that a MHAS packet payload is always bytealigned
so the truncation information is easily accessible on the fly and can be easily
inserted, removed or modified by e.g. a stream splicing device. A MPEG-H 3D Audio
stream could contain a MHAS packet type with pactype PACTYP_CUTRUNCATION for
every AU or for a suitable subset of AUs with isActive set to 0 . Then a stream splicing
device can modify this MHAS packet according to its need. Otherwise a stream splicing
device can easily insert such a MHAS packet without adding significant bitrate overhead
as it is described hereinafter. The largest granule size of MPEG-H 3D Audio is 4096
samples, so 13 bits for nTruncSamples are sufficient to signal all meaningful truncation
values. nTruncSamples and the 3 one bit flags together occupy 16 bits or 2 bytes so that
no further byte alignment is needed.
Figs. 13a-c illustrate how the method of CU truncation can be used to implement sample
accurate stream splicing.
Fig. 13a shows a video stream and an audio stream. At video frame number 5 the
program is switched to a different source. The alignment of video and audio in the new
source is different than in the old source. To enable sample accurate switching of the
decoded audio PCM samples at the end of the last CU of the old stream and at the
beginning of the new stream have to be removed. A short period of cross-fading in the
decoded PCM domain may be required to avoid glitches in the output PCM signal. Fig.
13a shows an example with concrete values. If for some reason the overlap of AUs/CUs is
not desired, the two possible solutions depicted in Fig. 13B) and Fig. 13C) exist. The first
AU of the new stream has to carry the configuration data for the new stream and all preroll
that is needed to initialize the decoder with the new configuration. This can be done by
means of an Immediate Playout Frame (IPF) that is defined in the MPEG-H 3D Audio
standard.
Another application of the CU truncation method is changing the configuration of a MPEGH
3D Audio stream. Different MPEG-H 3D Audio streams may have very different
configurations. E.g. a stereo program may be followed by a program with 11. 1 channels
and additional audio objects. The configuration will usually change at a video frame
boundary that is not aligned with the granules of the audio stream. The method of CU
truncation can be used to implement sample accurate audio configuration change as
illustrated in Fig. 14.
Fig. 14 shows a video stream and an audio stream. At video frame number 5 the program
is switched to a different configuration. The first CU with the new audio configuration is
aligned with the video frame at which the configuration change occurred. To enable
sample accurate configuration change audio PCM samples at the end of the last CU with
the old configuration have to be removed. The first AU with the new configuration has to
carry the new configuration data and all pre-roll that is needed to initialize the decoder
with the new configuration. This can be done by means of an Immediate Playout Frame
(IPF) that is defined in the MPEG-H 3D Audio standard. An encoder may use PCM audio
samples from the old configuration to encode pre-roll for the new configuration for
channels that are present in both configurations. Example: If the configuration change is
from stereo to 11. 1 , then the left and right channels of the new 1 . 1 configuration can use
pre-roll data form left and right from the old stereo configuration. The other channels of the
new 11. 1 configuration use zeros for pre-roll. Fig. 15 illustrates encoder operation and
bitstream generation for this example.
Fig. 16 shows further examples for spliceable or spliced audio data streams. See Fig.
16A, for example. Fig. 16A shows a portion out of a spliceable audio data stream
exemplarily comprising seven consecutive access units AUi to AU7. The second and sixth
access units are provided with a TU packet, respectively. Both are not used, i.e. nonactive,
by setting flag 52 to zero. The TU packet of access unit AU6 is comprised by an
access unit of the IPF type, i.e. it enables a splice back into the data stream. At B, Fig. 16
shows the audio data stream of A after insertion of an ad. The ad is coded into a data
stream of access units AU' to AU' 4. At C and D, Fig. 16 shows a modified case compared
to A and B. In particular, here the audio encoder of the audio data stream of access units
AUi... , has decided to change the coding settings somewhere within the audio frame of
access unit AU . Accordingly, the original audio data stream of C already comprises two
access units of timestamp 6.0, namely AU6 and Au with respective trailing end portion
and leading end portion indicated as to be discarded in playout, respectively. Here, the
truncation activation is already preset by the audio decoder. Nevertheless, the AU'
access unit is still usable as a splice-back-in access unit, and this possibility is illustrated
in D.
An example of changing the coding settings at the splice-out point is illustrated in E and F.
Finally, at G and H the example of A and B in Fig. 16 is extended by way of another TU
packet provided access unit AU5, which may serve as a splice-in or continue point.
As has been mentioned above, although the pre-provision of the access units of an audio
data stream with TU packets may be favorable in terms of the ability to take the bitrate
consumption of these TU packets into account at a very early stage in access unit
generation, this is not mandatory. For example, the stream splicer explained above with
respect to Figs. 7 to 9 may be modified in that the stream splicer identifies splice-in or
splice-out points by other means than the occurrence of a TU packet in the inbound audio
data stream at the first interface 102. For example, the stream splicer could react to the
external clock 122 also with respect to the detection of splice-in and splice-out points.
According to this alternative, the splice point setter 106 would not only set the TU packet
but also insert them into the data stream. However, please note that the audio encoder is
not freed from any preparation task: the audio encoder would still have to choose the IPF
coding mode for access units which shall serve as spiice-back-in points.
Finally, Fig. 17 shows that the favorable splice technique may also be used within an
audio encoder which is able to change between different coding configurations. The audio
encoder 70 in Fig. 17 is constructed in the same manner as the one of Fig. 5 , but this time
the audio encoder 70 is responsive to a configuration change trigger 200. That is, see for
example case C in Fig. 16: the audio encoding core 72 continuously encodes the audio
signal 12 into access units A to AU6. Somewhere within the audio frame of access unit
AU6, the configuration change time instant is indicated by trigger 200. Accordingly, audio
encoding core 72, using the same audio frame raster, also encodes the current audio
frame of access unit AU6 using a new configuration such as an audio coding mode
involving more coded audio channels or the like. The audio encoding core 72 encodes the
audio frame the other time using the new configuration with additionally using the IPF
coding mode. This ends up into access unit AU' , which immediately follows an access
unit order. Both access units, i.e. access unit AU and access unit AU', are provided with
TU packets by TU packet inserter 74, the former one having a trailing end portion
indicated so as to be discarded in playout and the latter one having a leading end portion
indicated as to be discarded in playout. The latter one may, as it is an IPF access unit,
also serve as a splice-back-in point.
For all of the above-described embodiments it should be noted that, possibly, cross-fading
is performed at the decoder between the audio signal reconstructed from the
subsequence of AUs of the spliced audio data stream up to a splice-out AU (such as AU,),
which is actually supposed to terminate at the leading end of the trailing end portion of the
audio frame of this splice-out AU on the one hand and the audio signal reconstructed from
the subsequence of AUs of the spliced audio data stream from the AU immediately
succedding the splice-out AU (such as AU'i) which may be supposed to start rightaway
from the leading end of audio frame of the successor AU, or at the trailing end of the
leading end portion of the audio frame of this successor AU: That is, within a temporal
interval surrounding and crossing the timestant where the portions of the immediately
consecutive AUs, to be played-out abut each other, the actually played-out audio signal as
played out from the spliced audio data stream by the decoder could be formed by a
combination of the audio frames of both immediately abutting AUs with a combinational
contribution of the audio frame of the successor AU temporally increasing within this
temporal interval and the combinational contribution of the audio frame of the splice-out
AU temporally decreasing in the temporal interval. Similarly, cross fading could be
performed between splice-in AUs such as AUj and their immediate predecessor AUs
(such as AU'K ) , namely by forming the acutally played out audio signal by a combination of
the audio frame of the splice-in A U and the audio frame of the predecessor A U within a
time interval surrounding and crossing the time instant at which the leading end portion of
the splice-in A U's audio frame and the trailnng end portion of the predecessor A U's audio
frame abut each other.
Using another wording, above embodiments, inter alias revealed, a possibility to exploit
bandwidth available by the transport stream, and available decoder MHz: a kind of Audio
Splice Point Message is sent along with the audio frame it would replace. Both the
outgoing audio and the incoming audio around the splice point are decoded and a
crossfade between them may be performed. The Audio Splice Point Message merely tells
the decoders where to do the crossfade. This is in essence a "perfect" splice because the
splice occurs correctly registered in the PCM domain.
Thus, above description revealed, inter alias, the following aspects:
A 1. Spliceable audio data stream 40, comprising:
a sequence of payload packets 16, each of the payload packets belonging to a respective
one of a sequence of access units 18 into which the spliceable audio data stream is
partitioned, each access unit being associated with a respective one of audio frames 14 of
an audio signal 12 which is encoded into the spliceable audio data stream in units of the
audio frames; and
a truncation unit packet 42; 58 inserted into the spliceable audio data stream and being
settable so as to indicate, for a predetermined access unit, an end portion 44; 56 of an
audio frame with which the predetermined access unit is associated, as to be discarded in
playout.
A2. Spliceable audio data stream according to aspect A 1, wherein the end portion of
the audio frame is a trailing end portion 44.
A3. Spliceable audio data stream according to aspect A 1 or A2, wherein the spliceable
audio data stream further comprises:
a further truncation unit packet 58 inserted into the spliceable audio data stream
and being settable so as to indicate for a further predetermined access unit, an end
portion 44; 56 of a further audio frame with which the further predetermined access unit is
associated, as to be discarded in playout.
A4. Spliceable audio data stream according to aspect A3, wherein the end portion of
the further audio frame is a leading end portion 56.
A5. Spliceable audio data stream according to aspect A3 or A4, wherein the truncation
unit packet 42 and the further truncation unit packet 58 comprise a splice-out syntax
element 50, respectively, which indicates whether the respective one of the truncation unit
packet or the further truncation unit packet relates to a splice-out access unit or not.
A6. Spliceable audio data stream according to any of aspects A3 to A5, wherein the
predetermined access unit such as All, has encoded thereinto the respective associated
audio frame in a manner so that a reconstruction thereof at decoding side is dependent on
an access unit immediately preceding the predetermined access unit, and a majority of
the access units has encoded thereinto the respective associated audio frame in a
manner so that the reconstruction thereof at decoding side is dependent on the respective
immediately preceding access unit, and the further predetermined access unit AU has
encoded thereinto the respective associated audio frame in a manner so that the
reconstruction thereof at decoding side is independent from the access unit immediately
preceding the further predetermined access unit, thereby allowing immediate playout.
A7. Spliceable audio data stream according to aspect A6, wherein the truncation unit
packet 42 and the further truncation unit packet 58 comprise a splice-out syntax element
50, respectively, which indicates whether the respective one of the truncation unit packet
or the further truncation unit packet relates to a splice-out access unit or not, wherein the
splice-out syntax element 50 comprised by the truncation unit packet indicates that the
truncation unit packet relates to a splice-out access unit and the syntax element
comprised by the further truncation unit packet indicates that the further truncation unit
packet relates not to a splice-out access unit.
A8. Spliceable audio data stream according to aspect A6, wherein the truncation unit
packet 42 and the further truncation unit packet 58 comprise a splice-out syntax element,
respectively, which indicates whether the respective one of the truncation unit packet or
the further truncation unit packet relates to a splice-out access unit or not, wherein the
syntax element 50 comprised by the truncation unit packet indicates that the truncation
unit packet relates to a splice-out access unit and the splice-out syntax element
comprised by the further truncation unit packet indicates that the further truncation unit
packet relates to a splice-out access unit, too, wherein the further truncation unit packet
comprises a leading/trailing-end truncation syntax element 54 and a truncation length
element 48, wherein the leading/trailing-end truncation syntax element is for indicating
whether the end portion of the further audio frame is a trailing end portion 44 or a leading
end portion 56 and the truncation length element is for indicating a length At of the end
portion of the further audio frame.
A9. Spliceable audio data stream according to any of aspects A 1 to A8, which is rate
controlled to vary around, and obey, a predetermined mean bitrate so that an integrated
bitrate deviation from the predetermined mean bitrate assumes, at the predetermined
access unit, a value within a predetermined interval which is less than ½ wide than a
range of the integrated bitrate deviation as varying over the complete spliceable audio
data stream.
A10. Spliceable audio data stream according to any of aspects A 1 to A8, which is rate
controlled to vary around, and obey, a predetermined mean bitrate so that an integrated
bitrate deviation from the predetermined mean bitrate assumes, at the predetermined
access unit, a fixed value smaller than ¾ of a maximum of the integrated bitrate deviation
as varying over the complete spliceable audio data stream.
A 1. Spliceable audio data stream according to any of aspects A 1 to A8, which is rate
controlled to vary around, and obey, a predetermined mean bitrate so that an integrated
bitrate deviation from the predetermined mean bitrate assumes, at the predetermined
access unit as well as other access units for which truncation unit packets are present in
the spliceable audio data stream, a predetermined value.
B 1. Spliced audio data stream, comprising:
a sequence of payload packets 16, each of the payload packets belonging to a
respective one of a sequence of access units 18 into which the spliced audio data stream
is partitioned, each access unit being associated with a respective one of audio frames
14;
a truncation unit packet 42; 58; 1 4 inserted into the spliced audio data stream and
indicating an end portion 44; 56 of an audio frame with which a predetermined access unit
is associated, as to be discarded in playout,
wherein in a first subsequence of payload packets of the sequence of payload
packets, each payload packet belongs to an access unit AU# of a first audio data stream
having encoded thereinto a first audio signal in units of audio frames of the first audio
signal, and the access units of the first audio data stream including the predetermined
access unit, and in a second subsequence of payload packets of the sequence of payload
packets, each payload packet belongs to access units AU' of a second audio data stream
having encoded thereinto a second audio signal in units of audio frames of the second
audio data stream,
wherein the first and the second subsequences of payload packets are
immediately consecutive with respect to each other and abut each other at the
predetermined access unit and the end portion is a trailing end portion 44 in case of the
first subsequence preceding the second subsequence and a leading end portion 56 in
case of the second subsequence preceding the first subsequence.
B2. Spliced audio data stream according to aspect B 1, wherein the first subsequence
precedes the second subsequence and the end portion as a trailing end portion 44.
B3. Spliced audio data stream according to aspect B 1 or B2, wherein the spliced audio
data stream further comprises a further truncation unit packet 58 inserted into the spliced
audio data stream and indicating a leading end portion 58 of a further audio frame with
which a further predetermined access unit AUj is associated, as to be discarded in
playout, wherein in a third subsequence of payload packets of the sequence of payload
packets, each payload packet belongs to access units AU" of a third audio data stream
having encoded therein a third audio signal, or to access units AU# of the first audio data
stream, following the access units of the first audio data stream to which the payload
packets of the first subsequence belong, wherein the access units of the second audio
data stream include the further predetermined access unit.
B4. Spliced audio data stream according to aspect B3, wherein a majority of the
access units of the spliced audio data stream including the predetermined access unit has
encoded thereinto the respective associated audio frame in a manner so that a
reconstruction thereof at decoding side is dependent on a respective immediately
preceding access unit, wherein the access unit such as AUI+1 , immediately succeeding the
predetermined access unit and forming an onset of the access units of the second audio
data stream has encoded thereinto the respective associated audio frame in a manner so
that the reconstruction thereof is independent from the predetermined access unit such as
AUi, thereby allowing immediate playout, and the further predetermined access unit AUj
has encoded thereinto the further audio frame in a manner so that the reconstruction
thereof is independent from the access unit immediately preceding further predetermined
access unit, thereby allowing immediate playout, respectively.
B5. Spliced audio data stream according to aspect B3 or B4, wherein the spliced audio
data stream further comprises an even further truncation unit packet 114 inserted into the
spliced audio data stream and indicating a trailing end portion 44 of an even further audio
frame with which the access unit such as AU' immediately preceding the further
predetermined access unit such as AUj is associated, as to be discarded in playout,
wherein the spliced audio data stream comprises timestamp information 24 indicating for
each access unit of the spliced audio data stream a respective timestamp at which the
audio frame with which the respective access unit is associated , is to be played out,
wherein a timestamp of the further predetermined access unit equals the timestamp of the
access unit immediately preceding the further predetermined access unit plus a temporal
length of the audio frame with which the access unit immediately preceding the further
predetermined access unit is associated , minus the sum of a temporal length of the
leading end portion of the further audio frame and the trailing end portion of the even
further audio frame or equals the timestamp of the access unit immediately preceding the
further predetermined access unit plus a temporal length of the audio frame with which the
access unit immediately preceding the further predetermined access unit is associated ,
minus the temporal length of the trailing end portion of the even further audio frame.
B6. Spliced audio data stream according to aspect B2, wherein the spliced audio data
stream further comprises an even further truncation unit packet 58 inserted into the
spliced audio data stream and indicating a leading end portion 56 of an even further audio
frame with which the access unit such as AUj immediately succeeding the predetermined
access unit such as AU is associated, as to be discarded in piayout, wherein the spliced
audio data stream comprises timestamp information 24 indicating for each access unit of
the spliced audio data stream a respective timestamp at which the audio frame with which
the respective access unit is associated , is to be played out, wherein a timestamp of the
access unit immediately succeeding the predetermined access unit equals the timestamp
of the predetermined access unit plus a temporal length of the audio frame with which the
predetermined access unit is associated minus the sum of a temporal length of the trailing
end portion of the audio frame with which the predetermined access unit is associated and
the leading end portion of the further even access unit or equals the timestamp of the
predetermined access unit plus a temporal length of the audio frame with which the
predetermined access unit is associated minus the temporal length of the trailing end
portion of the audio frame with which the predetermined access unit is associated.
B7. Spliced audio data stream according to aspect B6, wherein a majority of the
access units of the spliced audio data stream has encoded thereinto the respective
associated audio frame in a manner such that a reconstruction of thereof at decoding side
is dependent on a respective immediately preceding access unit, wherein the access unit
immediately succeeding the predetermined access unit and forming an onset of the
access units of the second audio data stream has encoded thereinto the respective
associated audio frame in a manner so that the reconstruction of thereof at decoding side
is independent from the predetermined access unit, thereby allowing immediate piayout.
B8. Spliced audio data stream according to aspect B7, wherein the first and second
audio data streams are encoded using different coding configurations, wherein the access
unit immediately succeeding the predetermined access unit and forming an onset of the
access units of the second audio data stream has encoded thereinto configuration data
cfg for configuring a decoder anew.
B9. Spliced audio data stream according to aspect B4, wherein the spliced audio data
stream further comprises an even even further truncation unit packet 112 inserted into the
spliced audio data stream and indicating a leading end portion of an even even further
audio frame with which the access unit immediately succeeding the predetermined access
unit is associated, as to be discarded in piayout, wherein the spliced audio data stream
comprises timestamp information 24 indicating for each access unit a respective
timestamp at which the audio frame with which the respective access unit is associated, is
to be played out, wherein a timestamp of the access unit immediately succeeding the
predetermined access unit is equal to the timestamp of the predetermined access unit
plus a temporal length of the audio frame associated with the predetermined access unit
minus the sum of a temporal length of the leading end portion of the even even further
audio frame and a temporal length of the trailing end portion of the audio frame associated
with the predetermined access unit or equal to the timestamp of the predetermined access
unit plus a temporal length of the audio frame associated with the predetermined access
unit minus the temporal length of the temporal length of the trailing end portion of the
audio frame associated with the predetermined access unit.
B 0. Spliced audio data stream according to aspect B4, B5 or B9, wherein a temporal
timestamp of the access unit immediately succeeding the predetermined access unit is
equal to the timestamp of the predetermined access unit plus a temporal length of the
audio frame with which the predetermined access unit is associated, minus a temporal
length of the trailing end portion of the audio frame with which the predetermined access
unit is associated.
C 1. Stream splicer for splicing audio data streams, comprising:
a first audio input interface 102 for receiving a first audio data stream 40
comprising a sequence of payioad packets 6 , each of which belongs to a respective one
of a sequence of access units 8 into which the first audio data stream is partitioned, each
access unit of the first audio data stream being associated with a respective one of audio
frames 14 of a first audio signal 2 which is encoded into the first audio data stream in
units of audio frames of the first audio signal;
a second audio input interface 104 for receiving a second audio data stream 110
comprising a sequence of payioad packets, each of which belongs to a respective one of
a sequence of access units into which the second audio data stream is partitioned, each
access unit of the second audio data stream being associated with a respective one of
audio frames of a second audio signal which is encoded into the second audio data
stream in units of audio frames of the second audio signal;
a splice point setter; and
a splice multiplexer,
wherein the first audio data stream further comprises a truncation unit packet 42;
58 inserted into the first audio data stream and being settable so as to indicate for a
predetermined access unit, an end portion 44; 56 of an audio frame with which a
predetermined access unit is associated, as to be discarded in playout, and the splice
point setter 06 is configured to set the truncation unit packet 42; 58 so that the truncation
unit packet indicates an end portion 44; 56 of the audio frame with which the
predetermined access unit is associated, as to be discarded in playout, or the splice point
setter 106 is configured to insert a truncation unit packet 42; 58 into the first audio data
stream and sets same so as to indicate for a predetermined access unit, an end portion
44; 56 of an audio frame with which a predetermined access unit is associated, as to be
discarded in playoutset the truncation unit packet 42; 58 so that the truncation unit packet
indicates an end portion 44; 56 of the audio frame with which the predetermined access
unit is associated, as to be discarded in playout; and
wherein the splice multiplexer 108 is configured to cut the first audio data stream
40 at the predetermined access unit so as to obtain a subsequence of payload packets of
the first audio data stream within which each payload packet belongs to a respective
access unit of a run of access units of the first audio data stream including the
predetermined access unit, and splice the subsequence of payload packets of the first
audio data stream and the sequence of payload packets of the second audio data stream
so that same are immediately consecutive with respect to each other and abut each other
at the predetermined access unit, wherein the end portion of the audio frame with which
the predetermined access unit is associated is a trailing end portion 44 in case of the
subsequence of payload packets of the first audio data stream preceding the sequence of
payload packets of the second audio data stream and a leading end portion 56 in case of
the subsequence of payload packets of the first audio data stream succeeding the
sequence of payload packets of the second audio data stream.
C2. Stream splicer according to aspect C 1, wherein the subsequence of payload
packets of the first audio data stream precedes the second subsequence the sequence of
payload packets of the second audio data stream and the end portion of the audio frame
with which the predetermined access unit is associated is a trailing end portion 44.
C3. Stream splicer according to aspect C2, wherein the stream splicer is configured to
inspect a splice-out syntax element 50 comprised by the truncation unit packet and to
perform the cutting and splicing on a condition whether the spiice-oui syntax element 50
indicates the truncation unit packet as relating to a splice-out access unit.
C4. Stream splicer according to any of aspects C 1 to C3, wherein the splice point
setter is configured to set a temporal length of the end portion so as to coincide with an
external clock.
C5. Stream splicer according to aspect C4, wherein the external clock is a video frame
clock.
C6. Spliced audio data stream according to aspect C2, wherein the second audio data
stream has, or the splice point setter 106 causes by insertion, a further truncation unit
packet 114 inserted into the second audio data stream 1 0 and settable so as to indicate
an end portion of a further audio frame with which a terminating access unit such as AU'
of the second audio data stream 110 is associated, as to be discarded in playout, and the
first audio data stream further comprises an even further truncation unit packet 58 inserted
into the first audio data stream 40 and settable so as to indicate an end portion of an even
further audio frame with which the even further predetermined access unit such as AUj is
associated, as to be discarded in playout, wherein a temporal distance between the audio
frame of the predetermined access unit such as AU, and the even further audio frame of
the even further predetermined access unit such as AUj coincides with a temporal length
of the second audio signal between a leading access unit such as AU' thereof
succeeding, after splicing, the predetermined access unit such as AU, and the trailing
access unit such as AU'«, wherein the splice-point setter 106 is configured to set the
further truncation unit packet 1 4 so that same indicates a trailing end portion 44 of the
further audio frame as to be discarded in playout, and the even further truncation unit
packet 58 so that same indicates a leading end portion of the even further audio frame as
to be discarded in playout, wherein the splice multiplexer 108 is configured to adapt
timestamp information 24 comprised by the second audio data stream 10 and indicating
for each access unit a respective timestamp at which the audio frame with which the
respective access unit is associated, is to be played out, so that a time stamp of a leading
audio frame which the leading access unit of the second audio data stream 110 is
associated coincides with the timestamp of the audio frame with which the predetermined
access unit is associated plus the temporal length of the audio frame with which the
predetermined access unit is associated minus the temporal length of the trailing end
portion of the audio frame with which the predetermined access unit is associated and the
splice-point setter 106 is configured to set the further truncation unit packet 14 and the
even further truncation unit packet 58 so that a timestamp of the even further audio frame
equals the timestamp of the further audio frame plus a temporal length of the further audio
frame minus the sum of a temporal length of the trailing end portion of the further audio
frame and the leading end portion of the even further audio frame.
C7. Spliced audio data stream according to aspect C2, wherein the second audio data
stream 1 0 has, or the splice point setter 106 causes by insertion, a further truncation unit
packet 112 inserted into the second audio data stream and settable so as to indicate an
end portion of a further audio frame with which a leading access unit such as A I of the
second audio data stream is associated, as to be discarded in playout, wherein the splicepoint
setter 106 is configured to set the further truncation unit packet 12 so that same
indicates a leading end portion of the further audio frame as to be discarded in playout,
wherein timestamp information 24 comprised by the first and second audio data streams
and indicating for each access unit a respective timestamp at which the audio frame with
which the respective access unit of the first and second audio data streams is associated,
is to be played out, are temporally aligned and the splice-point setter 106 is configured to
set the further truncation unit packet 112 so that a timestamp of the further audio frame
minus a temporal length of the audio frame with which the predetermined access unit
such as AUi is associated plus a temporal length of the leading end portion equals the
timestamp of the audio frame with which the predetermined access unit is associated plus
a temporal length of the audio frame with which the predetermined access unit is
associated minus the temporal length of the trailing end portion.
D 1. Audio decoder comprising:
an audio decoding core 162 configured to reconstruct an audio signal 12, in units
of audio frames 14 of the audio signal, from a sequence of payload packets 16 of an audio
data stream 120, wherein each of the payload packets belongs to a respective one of a
sequence of access units 18 into which the audio data stream is partitioned, wherein each
access unit is associated with a respective one of the audio frames; and
an audio truncator 164 configured to be responsive to a truncation unit packet 42;
58; 114 inserted into the audio data stream so as to truncate an audio frame associated
with a predetermined access unit so as to discard, in playing out the audio signal, an end
portion thereof indicated to be discarded in playout by the truncation unit packet.
D2. Audio decoder according to aspect D 1, wherein the end portion is a trailing end
portion 44 or a leading end portion 56.
D3. Audio decoder according to aspect D 1 or D2, wherein a majority of the access
units of the audio data stream have encoded thereinto the respective associated audio
frame in a manner so that the reconstruction thereof is dependent on a respective
immediately preceding access unit, and the audio decoding core 162 is configured to
reconstruct the audio frame with which each of the majority of access units is associated
depending on the respective immediately preceding access unit.
D4. Audio decoder according to aspect D3, wherein the predetermined access unit has
encoded thereinto the respective associated audio frame in a manner so that the
reconstruction thereof is independent from an access unit immediately preceding the
predetermined access unit, wherein the audio decoding unit 162 is configured to
reconstruct the audio frame with which the predetermined access unit is associated
independent from the access unit immediately preceding the predetermined access unit.
D5. Audio decoder according to aspect D3 or D4, wherein the predetermined access
unit has encoded thereinto configuration data and the audio decoding unit 162 is
configured to use the configuration data for configuring decoding options according to the
configuration data und apply the decoding options for reconstructing the audio frames with
which the predetermined access unit and a run of access units immediately succeeding
the predetermined access unit is associated.
D6. Audio decoder according to any of aspects D 1 to D5, wherein the audio data
stream comprises timestamp information 24 indicating for each access unit of the audio
data stream a respective timestamp at which the audio frame with which the respective
access unit is associated, is to be played out, wherein the audio decoder is configured to
playout the audio frames with temporally aligning leading ends of the audio frames
according to the timestamp information and with leaving-out the end portion of the audio
frame with which the predetermined access unit is associated.
D7. Audio decoder according to any of aspects D 1 to D6, configured to perform a
cross-fade at a junction of the end portion and a remaining portion of the audio frame.
E 1. Audio encoder comprising:
an audio encoding core 72 configured to encode an audio signal 12, in units of
audio frames 4 of the audio signal, into payload packets 16 of an audio data stream 40
so that each payload packet belongs to a respective one of access units 18 into which the
audio data stream is partitioned, each access unit being associated with a respective one
of the audio frames, and
a truncation packet inserter 74 configured to insert into the audio data stream a
truncation unit packet 44; 58 being settable so as to indicate an end portion of an audio
frame with which a predetermined access unit is associated, as being to be discarded in
playout.
E2. Audio encoder according to aspect E 1, wherein the audio encoder is configured to
generate a spliceable audio data stream according to any of aspects A 1 to A9.
E3. Audio encoder according to aspects E 1 or E2, wherein the audio encoder is
configured to select the predetermined access unit among the access units depending on
an external clock.
E4. Audio encoder according to aspect E3, wherein the external clock is a video frame
clock.
E5. Audio encoder according to any of aspects E 1 to E5, configured to perform a rate
control so that a bitrate of the audio data stream varies around, and obeys, a
predetermined mean bitrate so that an integrated bitrate deviation from the predetermined
mean bitrate assumes, at the predetermined access unit, a value within a predetermined
interval which is less than ½ wide than a range of the integrated bitrate deviation as
varying over the complete spliceable audio data stream.
E6. Audio encoder according to any of aspects E 1 to E5, configured to perform a rate
control so that a bitrate of the audio data stream varies around, and obeys, a
predetermined mean bitrate so that an integrated bitrate deviation from the predetermined
mean bitrate assumes, at the predetermined access unit, a fixed value smaller than ¾ of a
maximum of the integrated bitrate deviation as varying over the complete spliceable audio
data stream.
E7. Audio encoder according to any of aspects E 1 to E5, configured to perform a rate
control so that a bitrate of the audio data stream varies around, and obeys, a
predetermined mean bitrate so that an integrated bitrate deviation from the predetermined
mean bitrate assumes, at the predetermined access unit as well as other access units for
wich truncation unit packets are inserted into the audio data stream, a predetermined
value.
E8. Audio encoder according to any of aspects E 1 to E7, configured to perform a rate
control by logging a coded audio decoder buffer fill state so that a logged fill state
assumes, at the predetermined access unit, a predetermined value.
E9. Audio encoder according to aspect E8, wherein the predetermined value is
common among access units for which truncation unit packets are inserted into the audio
data stream.
E10. Audio encoder according to aspect E8, configured to signal the predetermined
value within the audio data stream.
Although some aspects have been described in the context of an apparatus, it is clear that
these aspects also represent a description of the corresponding method, where a block or
device corresponds to a method step or a feature of a method step. Analogously, aspects
described in the context of a method step also represent a description of a corresponding
block or item or feature of a corresponding apparatus. Some or all of the method steps
may be executed by (or using) a hardware apparatus, like for example, a microprocessor,
a programmable computer or an electronic circuit. In some embodiments, some one or
more of the most important method steps may be executed by such an apparatus.
The inventive spliced or splicable audio data streams can be stored on a digital storage
medium or can be transmitted on a transmission medium such as a wireless transmission
medium or a wired transmission medium such as the Internet.
Depending on certain implementation requirements, embodiments of the invention can be
implemented in hardware or in software. The implementation can be performed using a
digital storage medium, for example a floppy disk, a DVD, a Blu-Ray, a CD, a ROM, a
PROM, an EPROM, an EEPROM or a FLASH memory, having electronically readable
control signals stored thereon, which cooperate (or are capable of cooperating) with a
programmable computer system such that the respective method is performed. Therefore,
the digital storage medium may be computer readable.
Some embodiments according to the invention comprise a data carrier having
electronically readable control signals, which are capable of cooperating with a
programmable computer system, such that one of the methods described herein is
performed.
Generally, embodiments of the present invention can be implemented as a computer
program product with a program code, the program code being operative for performing
one of the methods when the computer program product runs on a computer. The
program code may for example be stored on a machine readable carrier.
Other embodiments comprise the computer program for performing one of the methods
described herein, stored on a machine readable carrier.
In other words, an embodiment of the inventive method is, therefore, a computer program
having a program code for performing one of the methods described herein, when the
computer program runs on a computer.
A further embodiment of the inventive methods is, therefore, a data carrier (or a digital
storage medium, or a computer-readable medium) comprising, recorded thereon, the
computer program for performing one of the methods described herein. The data carrier,
the digital storage medium or the recorded medium are typically tangible and/or nontransitionary.
A further embodiment of the inventive method is, therefore, a data stream or a sequence
of signals representing the computer program for performing one of the methods
described herein. The data stream or the sequence of signals may for example be
configured to be transferred via a data communication connection, for example via the
Internet.
A further embodiment comprises a processing means, for example a computer, or a
programmable logic device, configured to or adapted to perform one of the methods
described herein.
A further embodiment comprises a computer having installed thereon the computer
program for performing one of the methods described herein.
A further embodiment according to the invention comprises an apparatus or a system
configured to transfer (for example, electronically or optically) a computer program for
performing one of the methods described herein to a receiver. The receiver may, for
example, be a computer, a mobile device, a memory device or the like. The apparatus or
system may, for example, comprise a file server for transferring the computer program to
the receiver .
In some embodiments, a programmable logic device (for example a field programmable
gate array) may be used to perform some or all of the functionalities of the methods
described herein. In some embodiments, a field programmable gate array may cooperate
with a microprocessor in order to perform one of the methods described herein. Generally,
the methods are preferably performed by any hardware apparatus.
The apparatus described herein may be implemented using a hardware apparatus, or
using a computer, or using a combination of a hardware apparatus and a computer.
The methods described herein may be performed using a hardware apparatus, or using a
computer, or using a combination of a hardware apparatus and a computer.
The above described embodiments are merely illustrative for the principles of the present
invention. It is understood that modifications and variations of the arrangements and the
details described herein will be apparent to others skilled in the art. It is the intent,
therefore, to be limited only by the scope of the impending patent claims and not by the
specific details presented by way of description and explanation of the embodiments
herein.
References
METHOD AND ENCODER AND DECODER FOR SAMPLE-ACCURATE
REPRESENTATION OF AN AUDIO SIGNAL, IIS1 b- 0 F51302 WO-ID,
FH1 10401 PID
ISO/IEC 23008-3, Information technology - High efficiency coding and media
delivery in heterogeneous environments - Part 3 : 3D audio
ISO/IEC DTR 14496-24: Information technology - Coding of audio-visual objects -
Part 24: Audio and systems interaction

Claims
Spliceable audio data stream (40), comprising:
a sequence of payload packets (16), each of the payload packets belonging to a
respective one of a sequence of access units (18) into which the spliceable audio
data stream is partitioned, each access unit being associated with a respective one
of audio frames (14) of an audio signal (12) which is encoded into the spliceable
audio data stream in units of the audio frames; and
a truncation unit packet (42; 58) inserted into the spliceable audio data stream and
being settable so as to indicate, for a predetermined access unit, an end portion
(44; 56) of an audio frame with which the predetermined access unit is associated,
as to be discarded in playout.
Spliceable audio data stream according to claim 1, wherein the spliceable audio
data stream further comprises:
a further truncation unit packet (58) inserted into the spliceable audio data stream
and being settable so as to indicate for a further predetermined access unit, an
end portion (44; 56) of a further audio frame with which the further predetermined
access unit is associated, as to be discarded in playout.
Spliceable audio data stream according to claim 2 , wherein the predetermined
access unit has encoded thereinto the respective associated audio frame in a
manner so that a reconstruction thereof at decoding side is dependent on an
access unit immediately preceding the predetermined access unit, and a majority
of the access units has encoded thereinto the respective associated audio frame in
a manner so that the reconstruction thereof at decoding side is dependent on the
respective immediately preceding access unit, and the further predetermined
access unit has encoded thereinto the respective associated audio frame in a
manner so that the reconstruction thereof at decoding side is independent from the
access unit immediately preceding the further predetermined access unit, thereby
allowing immediate playout.
WO 2016/038034 PCT/EP2015/070493
4 . Spliceable audio data stream according to claim 3 , wherein the truncation unit
packet (42) and the further truncation unit packet (58) comprise a splice-out syntax
element (50), respectively, which indicates whether the respective one of the
truncation unit packet or the further truncation unit packet relates to a splice-out
access unit or not, wherein the splice-out syntax element (50) comprised by the
truncation unit packet indicates that the truncation unit packet relates to a spliceout
access unit and the syntax element comprised by the further truncation unit
packet indicates that the further truncation unit packet relates not to a splice-out
access unit.
5 . Spliceable audio data stream according to claim 3 , wherein the truncation unit
packet (42) and the further truncation unit packet (58) comprise a splice-out syntax
element, respectively, which indicates whether the respective one of the truncation
unit packet or the further truncation unit packet relates to a splice-out access unit
or not, wherein the syntax element (50) comprised by the truncation unit packet
indicates that the truncation unit packet relates to a splice-out access unit and the
splice-out syntax element comprised by the further truncation unit packet indicates
that the further truncation unit packet relates to a splice-out access unit, too,
wherein the further truncation unit packet comprises a leading/trailing-end
truncation syntax element (54) and a truncation length element (48), wherein the
leading/trailing-end truncation syntax element is for indicating whether the end
portion of the further audio frame is a trailing end portion (44) or a leading end
portion (56) and the truncation length element is for indicating a length (At) of the
end portion of the further audio frame.
6 . Spliced audio data stream, comprising:
a sequence of payload packets(16), each of the payload packets belonging to a
respective one of a sequence of access units (18) into which the spliced audio
data stream is partitioned, each access unit being associated with a respective one
of audio frames (14);
a truncation unit packet (42; 58; 114) inserted into the spliced audio data stream
and indicating an end portion (44; 56) of an audio frame with which a
predetermined access unit is associated, as to be discarded in playout,
6/038034 PCT/EP2015/070493
wherein in a first subsequence of payload packets of the sequence of payload
packets, each payload packet belongs to an access unit (AU#) of a first audio data
stream having encoded thereinto a first audio signal in units of audio frames of the
first audio signal, and the access units of the first audio data stream including the
predetermined access unit, and in a second subsequence of payload packets of
the sequence of payload packets, each payload packet belongs to access units
(AU' ) of a second audio data stream having encoded thereinto a second audio
signal in units of audio frames of the second audio data stream,
wherein the first and the second subsequences of payload packets are
immediately consecutive with respect to each other and abut each other at the
predetermined access unit and the end portion is a trailing end portion (44) in case
of the first subsequence preceding the second subsequence and a leading end
portion (56) in case of the second subsequence preceding the first subsequence.
Spliced audio data stream according to claim 6 , wherein the spliced audio data
stream further comprises a further truncation unit packet (58) inserted into the
spliced audio data stream and indicating a leading end portion (58) of a further
audio frame with which a further predetermined access unit is associated, as to be
discarded in playout, wherein in a third subsequence of payload packets of the
sequence of payload packets, each payload packet belongs to access units (AU"#)
of a third audio data stream having encoded therein a third audio signal, or to
access units (AU#) of the first audio data stream, following the access units of the
first audio data stream to which the payload packets of the first subsequence
belong, wherein the access units of the second audio data stream include the
further predetermined access unit.
Spliced audio data stream according to claim 7 , wherein a majority of the access
units of the spliced audio data stream including the predetermined access unit has
encoded thereinto the respective associated audio frame in a manner so that a
reconstruction thereof at decoding side is dependent on a respective immediately
preceding access unit, wherein the access unit immediately succeeding the
predetermined access unit and forming an onset of the access units of the second
audio data stream has encoded thereinto the respective associated audio frame in
a manner so that the reconstruction thereof is independent from the predetermined
access unit, thereby allowing immediate playout, and the further predetermined
WO 2016/038034 PCT/EP2015/070493
access unit has encoded thereinto the further audio frame in a manner so that the
reconstruction thereof is independent from the access unit immediately preceding
further predetermined access unit, thereby allowing immediate piayoui,
respectively.
9 . Spliced audio data stream according to claim 7 or 8 , wherein the spliced audio
data stream further comprises an even further truncation unit packet ( 1 4) inserted
into the spliced audio data stream and indicating a trailing end portion (44) of an
even further audio frame with which the access unit immediately preceding the
further predetermined access unit is associated, as to be discarded in playout,
wherein the spliced audio data stream comprises timestamp information (24)
indicating for each access unit of the spliced audio data stream a respective
timestamp at which the audio frame with which the respective access unit is
associated, is to be played out, wherein a timestamp of the further predetermined
access unit equals the timestamp of the access unit immediately preceding the
further predetermined access unit plus a temporal length of the audio frame with
which the access unit immediately preceding the further predetermined access unit
is associated, minus the sum of a temporal length of the leading end portion of the
further audio frame and the trailing end portion of the even further audio frame.
10. Spliced audio data stream according to claim 8 or 9 , wherein a temporal timestamp
of the access unit immediately succeeding the predetermined access unit is equal
to the timestamp of the predetermined access unit plus a temporal length of the
audio frame with which the predetermined access unit is associated, minus a
temporal length of the trailing end portion of the audio frame with which the
predetermined access unit is associated.
1. Stream splicer for splicing audio data streams, comprising:
a first audio input interface (102) for receiving a first audio data stream (40)
comprising a sequence of payload packets (16), each of which belongs to a
respective one of a sequence of access units (18) into which the first audio data
stream is partitioned, each access unit of the first audio data stream being
associated with a respective one of audio frames (14) of a first audio signal (12)
which is encoded into the first audio data stream in units of audio frames of the first
audio signal;
6/038034 PCT/EP2015/070493
a second audio input interface (104) for receiving a second audio data stream
( 1 10) comprising a sequence of payioad packets, each of which beiongs to a
respective one of a sequence of access units into which the second audio data
stream is partitioned, each access unit of the second audio data stream being
associated with a respective one of audio frames of a second audio signal
which is encoded into the second audio data stream in units of audio frames of the
second audio signal;
a splice point setter; and
a splice multiplexer,
wherein the first audio data stream further comprises a truncation unit packet (42;
58) inserted into the first audio data stream and being settable so as to indicate for
a predetermined access unit, an end portion (44; 56) of an audio frame with which
a predetermined access unit is associated, as to be discarded in playout, and the
splice point setter ( 106) is configured to set the truncation unit packet (42; 58) so
that the truncation unit packet indicates an end portion (44; 56) of the audio frame
with which the predetermined access unit is associated, as to be discarded in
playout, or the splice point setter (106) is configured to insert a truncation unit
packet (42; 58) into the first audio data stream and sets same so as to indicate for
a predetermined access unit, an end portion (44; 56) of an audio frame with which
a predetermined access unit is associated, as to be discarded in playout set the
truncation unit packet (42; 58) so that the truncation unit packet indicates an end
portion (44; 56) of the audio frame with which the predetermined access unit is
associated, as to be discarded in playout; and
wherein the splice multiplexer (108) is configured to cut the first audio data stream
(40) at the predetermined access unit so as to obtain a subsequence of payioad
packets of the first audio data stream within which each payioad packet belongs to
a respective access unit of a run of access units of the first audio data stream
including the predetermined access unit, and splice the subsequence of payioad
packets of the first audio data stream and the sequence of payioad packets of the
second audio data stream so that same are immediately consecutive with respect
to each other and abut each other at the predetermined access unit, wherein the
6/038034 PCT/EP2015/070493
end portion of the audio frame with which the predetermined access unit is
associated is a trailing end portion (44) in case of the subsequence of payload
packets of the first audio data stream preceding the sequence of payload packets
of the second audio data stream and a leading end portion (56) in case of the
subsequence of payload packets of the first audio data stream succeeding the
sequence of payload packets of the second audio data stream.
Stream splicer according to claim 1 , wherein the subsequence of payload packets
of the first audio data stream precedes the second subsequence the sequence of
payload packets of the second audio data stream and the end portion of the audio
frame with which the predetermined access unit is associated is a trailing end
portion (44).
Stream splicer according to claim 1 or 12, wherein the splice point setter is
configured to set a temporal length of the end portion so as to coincide with an
external clock.
Spliced audio data stream according to claim 12, wherein the second audio data
stream has, or the splice point setter (106) causes by insertion, a further truncation
unit packet ( 1 14) inserted into the second audio data stream ( 1 10) and settable so
as to indicate an end portion of a further audio frame with which a terminating
access unit of the second audio data stream ( 1 10) is associated, as to be
discarded in playout, and the first audio data stream further comprises an even
further truncation unit packet (58) inserted into the first audio data stream (40) and
settable so as to indicate an end portion of an even further audio frame with which
the even further predetermined access unit is associated, as to be discarded in
playout, wherein a temporal distance between the audio frame of the
predetermined access unit and the even further audio frame of the even further
predetermined access unit coincides with a temporal length of the second audio
signal between a leading access unit thereof succeeding, after splicing, the
predetermined access unit and the trailing access unit, wherein the splice-point
setter (106) is configured to set the further truncation unit packet ( 1 14) so that
same indicates a trailing end portion (44) of the further audio frame as to be
discarded in playout, and the even further truncation unit packet (58) so that same
indicates a leading end portion of the even further audio frame as to be discarded
in playout, wherein the splice multiplexer (108) is configured to adapt timestamp
6/038034 PCT/EP2015/070493
information (24) comprised by the second audio data stream ( 0) and indicating
for each access unit a respective timestamp at which the audio frame with which
the respective access unit is associated, is to be played out, so that a time stamp
of a leading audio frame which the leading access unit of the second audio data
stream ( 1 10) is associated coincides with the timestamp of the audio frame with
which the predetermined access unit is associated plus the temporal length of the
audio frame with which the predetermined access unit is associated minus the
temporal length of the trailing end portion of the audio frame with which the
predetermined access unit is associated and the splice-point setter (106) is
configured to set the further truncation unit packet ( 1 14) and the even further
truncation unit packet (58) so that a timestamp of the even further audio frame
equals the timestamp of the further audio frame plus a temporal length of the
further audio frame minus the sum of a temporal length of the trailing end portion
of the further audio frame and the leading end portion of the even further audio
frame.
Spliced audio data stream according to claim 12, wherein the second audio data
stream ( 1 10) has, or the splice point setter (106) causes by insertion, a further
truncation unit packet ( 1 12) inserted into the second audio data stream and
settable so as to indicate an end portion of a further audio frame with which a
leading access unit of the second audio data stream is associated, as to be
discarded in playout, wherein the splice-point setter (106) is configured to set the
further truncation unit packet ( 1 12) so that same indicates a leading end portion of
the further audio frame as to be discarded in playout, wherein timestamp
information (24) comprised by the first and second audio data streams and
indicating for each access unit a respective timestamp at which the audio frame
with which the respective access unit of the first and second audio data streams is
associated, is to be played out, are temporally aligned and the splice-point setter
( 106) is configured to set the further truncation unit packet so that a timestamp of
the further audio frame minus a temporal length of the audio frame with which the
predetermined access unit is associated plus a temporal length of the leading end
portion equals the timestamp of the audio frame with which the predetermined
access unit is associated plus a temporal length of the audio frame with which the
predetermined access unit is associated minus the temporal length of the trailing
end portion.
WO 2016/038034 PCT/EP2015/070493
16. Audio decoder comprising:
an audio decoding core (162) configured to reconstruct an audio signal (12), in
units of audio frames (14) of the audio signal, from a sequence of payload packets
(16) of an audio data stream ( 120), wherein each of the payload packets belongs
to a respective one of a sequence of access units (18) into which the audio data
stream is partitioned, wherein each access unit is associated with a respective one
of the audio frames; and
an audio truncator (164) configured to be responsive to a truncation unit packet
(42; 58; 114) inserted into the audio data stream so as to truncate an audio frame
associated with a predetermined access unit so as to discard, in playing out the
audio signal, an end portion thereof indicated to be discarded in playout by the
truncation unit packet.
17. Audio encoder comprising:
an audio encoding core (72) configured to encode an audio signal (12), in units of
audio frames (14) of the audio signal, into payload packets (16) of an audio data
stream (40) so that each payload packet belongs to a respective one of access
units (18) into which the audio data stream is partitioned, each access unit being
associated with a respective one of the audio frames, and
a truncation packet inserter (74) configured to insert into the audio data stream a
truncation unit packet (44; 58) being settable so as to indicate an end portion of an
audio frame with which a predetermined access unit is associated, as being to be
discarded in playout.
18 . Method for splicing audio data streams comprising a first audio data stream (40)
comprising a sequence of payload packets (16), each of which belongs to a
respective one of a sequence of access units (18) into which the first audio data
stream is partitioned, each access unit of the first audio data stream being
associated with a respective one of audio frames (14) of a first audio signal (12)
which is encoded into the first audio data stream in units of audio frames of the first
audio signal; and a second audio data stream ( 10) comprising a sequence of
payload packets, each of which belongs to a respective one of a sequence of
6/038034 PCT/EP2015/070493
access units into which the second audio data stream is partitioned, each access
unit of the second audio data stream being associated with a respective one of
audio frames of a second audio signai which is encoded into the second audio
data stream in units of audio frames of the second audio signal;
wherein
the first audio data stream further comprises a truncation unit packet (42; 58)
inserted into the first audio data stream and being settable so as to indicate for a
predetermined access unit, an end portion (44; 56) of an audio frame with which a
predetermined access unit is associated, as to be discarded in playout, and the
method comprises setting the truncation unit packet (42; 58) so that the truncation
unit packet indicates an end portion (44; 56) of the audio frame with which the
predetermined access unit is associated, as to be discarded in playout, or the
method comprises inserting a truncation unit packet (42; 58) into the first audio
data stream and sets same so as to indicate for a predetermined access unit, an
end portion (44; 56) of an audio frame with which a predetermined access unit is
associated, as to be discarded in playout and setting the truncation unit packet (42;
58) so that the truncation unit packet indicates an end portion (44; 56) of the audio
frame with which the predetermined access unit is associated, as to be discarded
in playout; and
the method further comprises cutting the first audio data stream (40) at the
predetermined access unit so as to obtain a subsequence of payload packets of
the first audio data stream within which each payload packet belongs to a
respective access unit of a run of access units of the first audio data stream
including the predetermined access unit, and splicing the subsequence of payload
packets of the first audio data stream and the sequence of payload packets of the
second audio data stream so that same are immediately consecutive with respect
to each other and abut each other at the predetermined access unit, wherein the
end portion of the audio frame with which the predetermined access unit is
associated is a trailing end portion (44) in case of the subsequence of payload
packets of the first audio data stream preceding the sequence of payload packets
of the second audio data stream and a leading end portion (56) in case of the
subsequence of payload packets of the first audio data stream succeeding the
sequence of payload packets of the second audio data stream.
6/038034 PCT/EP2015/070493
Audio decoding method comprising:
reconstructing an audio signal (12), in units of audio frames (14) of the audio
signal, from a sequence of payload packets (16) of an audio data stream (120),
wherein each of the payload packets belongs to a respective one of a sequence of
access units (18) into which the audio data stream is partitioned, wherein each
access unit is associated with a respective one of the audio frames; and
responsive to a truncation unit packet (42; 58; 114) inserted into the audio data
stream, truncating an audio frame associated with a predetermined access unit so
as to discard, in playing out the audio signal, an end portion thereof indicated to be
discarded in playout by the truncation unit packet.
Audio encoding method comprising:
encoding an audio signal (12), in units of audio frames (14) of the audio signal, into
payload packets (16) of an audio data stream (40) so that each payload packet
belongs to a respective one of access units (18) into which the audio data stream
is partitioned, each access unit being associated with a respective one of the audio
frames, and
inserting into the audio data stream a truncation unit packet (44; 58) being settable
so as to indicate an end portion of an audio frame with which a predetermined
access unit is associated, as being to be discarded in playout.
Computer readable digital storage medium having stored thereon a computer
program having a program code for performing, when running on a computer, a
method according to any of claims 18 to 20.