1. An audio signal processing device comprising:
a selection unit configured to select, f rommultichannel audio signals, audio signals of a channel of a dialogue sound and audio signals of plural channels to be downmixed, on the basis of information related to each channel of the multichannel audio signals;
a downmixing unit configured to downmix the audio signals of the plural channels to be downmixed into audio signals of one or more channels; and
an addition unit configured to add the audio signals of the channel of a dialogue sound to audio channels of a predetermined channel among the one or more channels obtained by the downmixing.
2. The audio signal processing device according to claim
1, wherein
the addition unit adds the audio signals of the channel of a dialogue sound to the predetermined channel that is a channel specified by addition destination information indicating a destination to add the audio signals of the channel of a dialogue sound.
3. The audio signal processing device according to claim
2, further comprising
a gain correction unit configured to perform a gain correction of the audio sounds of the channel of a dialogue sound on the basis of gain information indicating a gain of the audio signals of the channel of a dialogue sound at a timing of addition to the audio signals of the predetermined channel,

wherein the addition unit adds the audio signals in which the gain is corrected by the gain correction unit to the audio signals of the predetermined channel.
4. The audio signal processing device according to claim
3, further comprising
an extraction unit configured to extract the information related to each channel, the addition destination information, and the gain information from a bit stream.
5. The audio signal processing device according to claim
4,
wherein the extraction unit further extracts the encoded multichannel audio signals from the bit stream, and
the audio signal processing device further comprises a decoding unit configured to decode the encoded multichannel audio signals and output to the selection unit.
6. The audio signal processing device according to claim
1, wherein
the downmixing unit performs multiple-stage downmixing on the audio signals of the plural channels to be downmixed, and
the addition unit adds the audio signals of the channel of a dialogue sound to the audio signals of the predetermined channel among the audio signals of the one or more channels obtained in the multiple-stage downmixing.
7. An audio signal processing method comprising the steps
of:
selecting, from multichannel audio signals, audio

signals of a channel of a dialogue sound and audio signals of plural channels to be downmixed, on the basis of information related to each channel of the multichannel audio signals;
downmixing the audio signals of the plural channels to be downmixed into audio signals of one or more channels; and
adding the audio signals of the channel of a dialogue sound to audio signals of a predetermined channel among the audio signals of the one or more channels obtained in the downmixing.
8. A program that causes a computer to execute the steps
comprising:
selecting, from multichannel audio signals, audio signals of a channel of a dialogue sound and audio signals of plural channels to be downmixed, on the basis of information related to each channel of the multichannel audio signals;
downmixing the audio signals of the plural channels to be downmixed into audio signals of one or more channels; and
adding the audio signals of the channel of a dialogue sound to the audio signals of a predetermined channel among the audio signals of the one or more channels obtained in the downmixing.
9. An encoding device comprising:
an encoding unit configured to encode multichannel audio signals;
a generation unit configured to generate identification information, which indicates whether or not each channel of themultichannel audio signals is a channel of a dialogue sound; i and
a packing unit configured to generate a bit stream

including the encoded multichannel audio signals and the identification information.
10. The encoding device according to claim 9, wherein
when the multichannel audio signals are downmixed, the
generation unit further generates addition destination information, which indicates a channel of audio signals as a destination to add the audio signals of the channel of a dialogue sound among audio signals of one or more channels obtained by downmixing, and
the packing unit generates the bit stream including the encoded multichannel audio signals, the identification information, and the addition destination information.
11. The encoding device according to claim 10, wherein
the generation unit further generates gain information
of the audio signals of the channel of a dialogue sound at a timing of addition to a channel indicated by the addition destination information, and
the packing unit generates the bit stream including the encoded multichannel audio signals, the identification information, the addition destination information, and the gain information.
12. An encoding method comprising the steps of:
encoding multichannel audio signals;
generating identification information, which indicates whether or not each channel of the multichannel audio signals is a channel of a dialogue sound, and
generating a bit stream including the encoded multichannel audio signals and the identification

information.
13. A program that causes a computer to execute a process including the steps comprising:
. encoding multichannel audio signals;
generating identification information, which indicates whether or not each channel of the multichannel audio signals is a "channel of a dialogue sound; and
generating a bit stream including the encoded multichannel audio signals and the identification information.