FIELD OF THE INVENTION The present invention relates generally to information recording and reproduction, and more particularly, to recording audio and video signals or the like together with additional information related to those signals, and selectively reproducing the audio/video signals based on the additional information. BACKGROUND OF THE INVENTION Presently, analog-type video tape recorders (VTRs) are commonly used to record and reproduce analog video and audio signals of a television broadcast. It is contemplated that digital data corresponding to such analog video and audio signals will be commonly recorded on a digital storage medium such as an optical disk or a magnetic hard disk. With conventional VTRs, reproduction is facilitated by introducing various identifying signals during the recording process. For example, one type of identifying signal is used to identify whether a television broadcast is a bilingual broadcast or a stereo broadcast. As a result, a television receiver can discriminate between these two types of broadcasts and control the audio signal output method accordingly. Contemporary optical disks and hard disks have superior accossibility, i.e., random access capability, as compared to analog magnetic tapes. As such, various fast viewing and listening methods are now being considered for these disks, such aa speech speed conversion and selective skipping of song contents. In contrast, conventional VTRs lack such capability. Some prior art VTRs include an automatic audio selection function or the like, while others have a speech speed conversion feature. A drawback of the speech speed conversion feature, however, is that video and audio are processed independently. This is problematic in that the output audio and video may become unsynchronized, resulting in unnatural audiovisual output, e.g., lips moving before or after the audio is produced. Conventional laser disc players ("LDPs") are capable of header search for karaoke use (i.e., for in use in a sing-along machine). However, in the case of ordinary broadcasts, users in many instances desire to view conversational-type programs between musical performance programs. In these cases, the conventional LDP, which is capable only of header search, is inadequate. OBJECTS AND SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a recording apparatus capable of recording an audio or audiovisual signal on a digital storage medium, while concomitantly analyzing its characteristics over time for particular audio types and storing information indicative of such characteristics on the storage medium. It is a further object of the invention to provide a reproduction apparatus that allows for selective reproduction of the audio or audiovisual signal so recorded based on user selection of a particular audio type. It is another object of the invention to provide recording and reproduction apparatuses with enhanced features. In an illustrative embodiment of the invention, there is provided an information recording apparatus for recording at least an audio signal onto a recording medium, which includes detection circuitry for detecting a feature of the audio signal, and recording circuitry for recording together with the audio signal additional information that corresponds to the detected feature. Preferably, features of the audio signal are detected in a time-segmented manner, such that segments or frames of the audio signal are each characterized. For example, features that may be detected by the detection circuitry may include: whether a given segment comprises muted audio; whether it comprises music; or whether it comprises conversational speech. With the feature information stored on the recording medium, versatility during reproduction is advantageously possible, thereby providing the uaer with a highly versatile tool during playback. For instance, the uaer is able to skip portions of the recorded material having an undesired audio type or types, or to quickly locate a desired portion of the recorded material by selective skipping based on audio types. In another illustrative embodiment, there is provided an information reproduction apparatus for reproducing at least an audio signal corresponding to audio data recorded on a recording medium on which additional information relating to at least the audio signal is also recorded. The apparatus includes reading means for reading out a portion of the additional information prior to any reproduction of a corresponding portion of the audio signal; determining means for determining whether to reproduce the corresponding portion of the audio signal in accordance with the read-out portion of the additional information and a current operating mode; and control means for controlling reproduction of the corresponding portion of the audio signal in accordance-with a determination by the determining means. Accordingly, there is provided An information recording and reproducing apparatus for recording an audio visual signal onto a recording medium, characterized by: an audio features extraction system for performing a quadrature transform on the audio signal periodically at a predetermined time interval and for detecting a feature of the audio signal by determining a correlation between resulting energy components and energy distribution; and an audio recorder for recording additional information that corresponds to said detected feature onto the recording medium together with the audio signal and preferably a video recorder for recording video signal. Accordingly, there is also provided an information reproduction apparatus for reproducing an audio signal corresponding to audio data recorded on a recording medium on which audio signal and additional information relating to the audio signal is also recorded, said additional information corresponding to a detected feature of said audio signal obtained by performing a quadrature transform on the audio signal periodically at a predetermined time interval and detecting a feature of the audio signal by determining a correlation between resulting energy components and energy distribution, said information reproduction apparatus comprising; a reader for reading out a portion of the additional information prior to any reproduction of a corresponding portion of the audio signal; a subcode detecting system for determining whether to reproduce said corresponding portion of the audio signal in accordance with said readout portion of said additional information and a current operating mode; and a controller for controlling reproduction of the corresponding portion of the audio signal in accordance with a determination by said determining section. BRIEF DESCRIPTION OF THE DRAWINGS The following detailed description, given by way of example and not intended to limit the present invention solely thereto, will best be appreciated in conjunction with the accompanying drawings, in which like reference numerals denote like elements and parts, wherein: FIG. 1 is a block diagram of an illustrative configuration of an information recording apparatus according to an embodiment of the present invention; FIG. 2 illustrates an illustrative arrangement of storage regions on a disk; FIG. 3 is a flowchart showing the operation of the information recording apparatus of PIG. 1; FIGS. 4 and 5 are flowcharts showing a process of generating a subcode indicative of an audio feature; FIGS. 6 and 7 are timing diagrams showing output timing of signals flowing within the respective processing systems of PIG. 1; FIG. 8 is a block diagram showing an illustrative configuration of an information reproduction apparatus according to an embodiment of the invention; FIG. 9 is a flowchart showing the operation of the information reproduction apparatus of PIG. 8; FIG. 10 is a timing diagram showing output timing of signals flowing within the respective processing systems of PIG. 8; FIG. 11 is a block diagram showing an illustrative configuration of an information reproduction apparatus according to another embodiment of the invention; FIG. 12 is a flowchart illustrating the operation of the information reproduction apparatus of FIG. 11; and FIG. 13 is a timing diagram showing output timing of signals flowing within the respective processing systems of FIG. 11. DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS FIG. 1 is a block diagram of a first illustrative embodiment of the present invention, designated as recording apparatus 100. As will be described in detail below, recording apparatus 100 is configured to selectively receive various types of analog input signals, such as a television broadcast signal or a camera system output signal. The apparatus converts the selected input signal to a digital signal, and compresses and records the same on a digital storage medium such as an optical or magnetic disk. As the audio and video signals are received and recorded, characteristics of the audio signal are analyzed Over time so as to categorize its contents in a time-segmented manner. In particular, individual frames of the audio signal are analyzed to determine which frames or frame sequences correspond to, e.g., music, conversational speech, or muted audio. Each segment of the recorded audio program is thereby categorized. A user table of contents is then generated corresponding to the categorization of the audio signal. The table of contents is recorded onto the digital storage medium, either in a specific region of the recording medium, or distributed as subcodes in the same regions as the recorded audio/video data. The table of contents allows a user to play back a selected type of audio and associated video data while skipping other types, or to quickly access desired portions of the recorded audiovisual program by selective skipping of certain audio types, and so forth. Recording apparatus 100 will now be described in detail. Video signal processing system l is configured to receive an external input video signal, such as a VTR video output, and perform various kinds of processing on the signal such as automatic gain control {AGO . A camera signal processing system 2 operates to receive a video signal from a charge coupled device (CCD) camera or the like and convert it into a standard protocol signal such as a National Television System Committee (NTSC) video signal. Tuner system 3 receives a television broadcast signal via an antenna system (not shown), and converts a selected channel of the television signal into video and audio signals through video detection, video amplification and audio detection. Audio signal processing system 7 is adapted to receive and amplify an external audio signal, e.g., the audio output from the VTR supplying the video signal to system 1. A microphone input audio processing system 8 amplifies an audio signal inputted through a microphone and performs AGC processing thereon. The video output signals from each of systems 1, 2 and 3 are applied as inputs to video signal switching system 4, which switches a selected one of the video signals to its output in accordance with a selection control signal from system controller 14. Likewise, audio signal switching system 9 routes the selected one of the audio signals from systems 3, 7 and 8 to its output based on the control signal from system controller 14. In the video path, the analog video output of switching system 4 is applied to video signal A/D conversion system 5 where it is converted to a digital video signal and then quantized. The quantized, digital video signal is then compressed by video compressing and processing system 6 in accordance with a standard compression protocol such as the joint photographic experts group (JPEG) or the moving picture experts group (MPEG) schemes. The compressed video signal is applied to recording data processing system 17 and recorded in recording medium 18 as will be discussed more fully below. In the audio path of recording apparatus 100, the analog audio output of audio switching system 9 is converted to digital audio signal by audio signal A/D conversion system (A/D converter) 10. The digitized audio output from A/D converter 10 is applied to both an audio features extraction system 12 (detecting means) and to an audio signal band compression system 11, the latter of which compresses the audio when necessary in accordance with a standard protocol such as MPEG. Audio features extraction system 12 includes processing circuitry to analyze certain characteristics of the digital audio signal applied thereto from system 10, to thereby extract audio features from the signal. The quantized audio signal is quadrature.,- transformed in extraction system 12 based on operating parameters supplied thereto from system controller 14, and then subjected to a specified operation in accordance with an operating command also supplied by system controller 14. The audio signal is analyzed in extraction system 12 on a block by block basis, where each block corresponds to a specific time segment (e.g., frame or set of frames) of the audio signal to be recorded. By way of example, to determine which portions of the audio signal correspond to a mute condition, the audio signal may be analyzed in 0.02 second blocks to determine which blocks contain muted or low level audio. The audio signal is analyzed over larger blocks of time to determine which of the larger blocks contain audio corresponding to, e.g., instrument music, human speech or vocal music. Based on the results of the analysis performed by extraction system 12, subcodes are generated by a subcodes generation system 13 to characterize each such block of the audio signal. Certain subcodes are temporarily stored within memory 16. In particular, for each audio block of duration "Dl" (e.g., 0.02 seconds duration), a subcode "A" is generated as indicative of whether or not that block corresponds to muted audio. For each block of a longer duration "D2", a subcode "B" is generated which is indicative of the type of audio contained in tha't block, e.g., conversation, instrument music or vocal music. Subcodes A are directly transferred to recording data processing system 17, whereas subcodes B are transferred to memory circuit *£6 for temporary storage therein. Typically, when recording of audio/video data is complete, all subcodes B are transferred as a block from memory 16 to recording data processing system 17 (via subcodes generation system 13) under the control of system controller 14. In any event, as the analog audio signal is received by recording apparatus 100, it is digitized, compressed and recorded as data, generally in real time, on a predetermined portion of the recording medium 18. As the subcodes A and B are generated, a user table of contents (U-TOC) is generated to correlate the audio data being shored on recording medium-18 with the subcodes characterizing the respective segments of the audio data. The U-TOC is stored on recording medium 18. As shown in FIG. 2, the digitized audio data may be recorded on the outermost region of the disk, and the U-TOC data may be recorded on a predetermined area of the disk outside the innermost region where a table of contents (TOC) is recorded. System controller 14 is configured to control the respective processing systems by supplying control signals thereto based on a user's instruction inputted through recording control signal input system 15, e.g., a keyboard or the like. Recording data processing system 17 (recording means) operates to multiplex bit sequences that are supplied from video compression system 6, audio compression system 11, and subcodes generation system 13, and to transfer the multiplexed data to recording medium 18 and record the data thereon. (It is noted that some or all of the subcodes may optionally be transferred as a block without being multiplexed with the audio and video data, in which case recording system 17 juat records the block of subcodes on the recording medium without multiplexing). Recording medium 18 may be an optical disk, a hard disk, a memory card, or the like. FIG. 3 is a flowchart illustrating process steps executed within system controller 14 to control various aspects of the recording process of recording apparatus 100. At the outset (step SI) system controller 14 determines an operating mode based on a user's instruction input to input system 15, e.g, by detecting depression of a particular mode key. In step 32, it is ascertained whether the operating mode determined in step SI is a normal recording mode, i.e., a mode in which both video and audio signals are recorded. If so, the routine proceeds to step S3, where system controller 14 sets operation, parameters A, B, C, and D in the audio features extraction system 12. For reasons that will become apparent below, the values of parameters A-D are set in accordance with the type of audio signal selected by the user, e.g., audio signal from a television signal, VTR output or microphone. Thus, the values of parameters A-D correspond to the switching state of audio switching system 9, which is controlled by system controller 14. Before proceeding further with FIG. 3, reference is made to PIG. 4 which shows a flowchart illustrating a routine within audio features extraction system 12 and subcodes generation system 13. For the presently described embodiment, it is assumed that one data block contains N bits or bytes of audio data, where N is a predetermined integer. By way of example, one block may contain digitized audio data corresponding to a 0,02 second long segment of the input analog audio signal. It is further assumed that subcode A ia calculated on a block-by-block basis, and that subcode 8 ia calculated on an M-blocJc basis, where M is a specified integer. In step S21, audio features extraction system 12 receives operation parameters A, B, C, and D from system controller 14, which parameters have been set in accordance with the type of audio signal selected as discussed previously. If, in. step S22, it is determined that M blocks have not yet been processed, the single block process ("1-block process") of step 327 is executed. FIG, 5 is a flow chart illustrating the 1-block process. In step S31, a fast Fourier transform (FFT) is performed on a single block of the audio signal to determine the spectral components of the portion of the signal corresponding to that block. Next, in step S32, audio signal power is calculated from Nb frequency components that are specified by operation parameter B supplied from system controller 14. The portion of the input audio signal band to be used in calculating signal power is thus determined by parameter B. For example, an audio signal from a camera system includes a considerable amount of low frequency components such as zip, while an audio signal of a television broadcast includes a considerable amount of components at harmonic frequencies of the frame frequency. Hence, for the signal power calculation, noise-induced errors can be reduced by appropriately filtering out undesired frequencies in accordance with the type of audio signal being analyzed. In the next step, S33, it is ascertained whether or not the signal is mute. That is, if the calculated power value is smaller than parameter C, the signal is determined to be mute within the associated block. Optionally, when the computed power is larger than C, a further determination can be made as to whether the signal power is within