Abstract:
An audio mixing/reproducing device includes an audio decoder ( 11 ) configured to decode an encoded audio input signal, an audio mixer ( 13 ) configured to mix an audio signal output from the audio decoder ( 11 ) with a non-encoded external audio input signal, and an audio encoder ( 12 ) configured to encode an audio signal output from the audio mixer ( 13 ) to generate an encoded audio output signal, and in addition, a switch ( 14 ) configured to generate a switch signal for controlling operations of each of the audio decoder ( 11 ) and the audio encoder ( 12 ) in response to a switch activation signal. The audio decoder ( 11 ) and the audio encoder ( 12 ) each support a plurality of encoding schemes, and the switch ( 14 ), when switching the encoding scheme of the audio decoder ( 11 ) from a first encoding scheme to a second encoding scheme, controls the audio decoder ( 11 ) and the audio encoder ( 12 ) so that the encoding scheme of the audio encoder ( 12 ) is switched from the first encoding scheme to the second encoding scheme as in the audio decoder ( 11 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to the technical field of real-time mixing and reproduction of two or more audio signals. 
       BACKGROUND ART 
       [0002]    For editing apparatuses which link one encoded stream to some midpoint of another encoded stream, these streams being recorded on, for example, a digital versatile disk (DVD)—random access memory (RAM), to produce a single encoded stream, there is a known technique of decoding first and second streams using two decoders and selecting decoded data to perform reencoding only for a short period of time including periods of time before and after an editing point, and selecting streams as they are before editing for the other period of time so that one stream can be linked to any point of another stream while a degradation in image quality is reduced or prevented. In this case, only the audio of the first stream can be replaced with the audio of the second stream while the image of the first stream is not replaced with the image of the second stream (see PATENT DOCUMENT 1). 
       CITATION LIST 
     Patent Document 
       [0003]    PATENT DOCUMENT 1: Japanese Patent Laid-Open Publication No. 2000-165802 
       SUMMARY OF THE INVENTION 
     Technical Problem 
       [0004]    However, in the aforementioned conventional technique, two or more audio signals cannot be mixed or reproduced in real time. The aforementioned conventional technique is also not flexible or adaptable to various encoding techniques (encoding standards). 
         [0005]    It is an object of the present invention to provide an audio mixing/reproducing device which can mix and reproduce two or more audio signals in real time while supporting a plurality of encoding schemes. 
       Solution to the Problem 
       [0006]    To achieve the aforementioned object, the present invention employs a structure of an audio mixing/reproducing device including an audio decoding unit configured to decode an encoded audio input signal to generate a first audio signal, an audio mixing unit configured to mix the first audio signal with a non-encoded second audio signal to generate a third audio signal, an audio encoding unit configured to encode the third audio signal to generate an encoded audio output signal, and a switching unit configured to switch between operations of each of the audio decoding unit and the audio encoding unit. The audio decoding unit and the audio encoding unit each support two or more encoding schemes, and the switching unit, when switching the encoding scheme of the audio decoding unit from a first encoding scheme to a second encoding scheme, controls the audio decoding unit and the audio encoding unit so that the encoding scheme of the audio encoding unit is switched from the first encoding scheme to the second encoding scheme in synchronization with the switching of the encoding schemes in the audio decoding unit. 
       ADVANTAGES OF THE INVENTION 
       [0007]    According to the present invention, while two or more encoding schemes are supported, an encoded audio signal which is obtained by mixing with a non-encoded second audio signal (e.g., an external audio signal) can be output in real time using the same encoding scheme as that of the input. Therefore, a signal which is obtained by mixing an encoded audio signal which is, for example, read out from a medium with an external audio signal can be immediately written back into the medium. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a block diagram of an audio mixing/reproducing device according to a first embodiment of the present invention. 
           [0009]      FIG. 2  is a block diagram of an audio mixing/reproducing device according to a second embodiment of the present invention. 
           [0010]      FIG. 3  is a block diagram of an audio mixing/reproducing device according to a third embodiment of the present invention. 
           [0011]      FIG. 4  is a block diagram of an audio mixing/reproducing device according to a fourth embodiment of the present invention. 
           [0012]      FIG. 5  is a block diagram of an audio mixing/reproducing device according to a fifth embodiment of the present invention. 
           [0013]      FIG. 6  is a block diagram of an audio mixing/reproducing device according to a sixth embodiment of the present invention. 
           [0014]      FIG. 7  is a block diagram of an audio mixing/reproducing device according to a seventh embodiment of the present invention. 
       
    
    
     DESCRIPTION OF REFERENCE CHARACTERS 
       [0000]    
       
           11  Audio Decoder 
           12  Audio Encoder 
           13  Audio Mixer 
           14  Switch 
           15  Switch Time Adjuster 
           16  Control Determiner 
           17  External Audio Input Switch 
           18  Audio Output Switch 
           19  Audio Determiner 
           21  Image Decoder 
           22  Image Determiner 
           23  Sound Level Adjuster 
           24  Audio Output Switch 
           121 ,  122  Audio Encoder 
       
     
       DESCRIPTION OF EMBODIMENTS 
       [0029]    Embodiments of the present invention will be described in detail hereinafter with reference to the accompanying drawings. Although first and second encoding schemes described below are, for example, of the MPEG audio layer-3 (MP3) standard and the advanced audio coding (AAC) standard, the present invention is not limited to those specific encoding schemes. 
       First Embodiment 
       [0030]      FIG. 1  is a block diagram of a device according to a first embodiment of the present invention. In  FIG. 1 , the reference character  11  indicates an audio decoder which supports a first encoding scheme and a second encoding scheme, the reference character  12  indicates an audio encoder which supports the first and second encoding schemes, the reference character  13  indicates an two-input audio mixer, and the reference character  14  indicates a switch. The reference character S 1  indicates an encoded audio input signal, and the reference character S 2  indicates an encoded audio output signal. The reference character S 11  indicates a switch signal which is generated by the switch  14  and is used to switch between the encoding schemes of the audio decoder  11 . The reference character S 12  indicates a switch signal which is generated by the switch  14  and is used to switch between the encoding schemes of the audio encoder  12 . The reference character S 13  indicates an audio signal which is output by the audio decoder  11 , the reference character S 14  indicates a non-encoded external audio input signal, the reference character S 15  indicates an audio signal which is a mixture of the decoded audio signal S 13  and the external audio input signal S 14 , and the reference character S 17  indicates an encoding scheme switch activation signal which is externally input to the switch  14 . Encoding scheme switch activation is written in, for example, a video object (VOB) management area of DVDs, and can be detected by an external system, although the process of generating the encoding scheme switch activation is not specified in this embodiment. 
         [0031]    In the audio mixing/reproducing device of  FIG. 1 , the two switch signals S 11  and S 12  are synchronously generated in accordance with the switch activation signal S 17 , whereby the encoding schemes of the audio decoder  11  and the audio encoder  12  are simultaneously switched to the same scheme. The decoded audio signal S 13  is mixed with the external audio input signal S 14  by the audio mixer  13  before being encoded by the audio encoder  12  using the same encoding scheme with which the decoded audio signal S 13  was originally encoded. 
         [0032]    Therefore, two or more encoding schemes can be supported, and an encoded audio signal mixed with external audio can be generated using the same encoding scheme as that of the input. 
       Second Embodiment 
       [0033]      FIG. 2  is a block diagram of a device according to a second embodiment of the present invention. In  FIG. 2 , the reference character  15  indicates a switch time adjuster, the reference character  16  indicates a control determiner, and the reference character  17  indicates an external audio input switch. 
         [0034]    The control determiner  16  receives a user control signal S 16  indicating a user&#39;s instruction and determines a control, and outputs an encoding scheme switch activation signal S 17 , a select control signal S 18 , and an encoding scheme switch permission signal S 19  to the switch  14 , the external audio input switch  17 , and the switch time adjuster  15 , respectively. The external audio input switch  17  switches between the active mode and the inactive mode of the external audio input signal S 14  based on the select control signal S 18  from the control determiner  16 . The reference character S 141  indicates a signal which is input as a second input signal to the audio mixer  13  based on the active-mode external audio input signal S 14 . The switch  14  outputs two switch signals S 11  and S 12  to an audio decoder  11  and an audio encoder  12 , respectively, based on the switch activation signal S 17  from the control determiner  16  to specify an encoding scheme for the audio decoder  11  and the audio encoder  12 . The switch time adjuster  15  adjusts the timing of transmission of the encoding scheme to the audio encoder  12  based on the switch permission signal S 19  from the control determiner  16 . The reference character S 20  indicates a switch signal whose timing has been adjusted. 
         [0035]    In the audio mixing/reproducing device of  FIG. 2 , the control determiner  16  receives the user control signal S 16  and then transmits the switch activation signal S 17  before the two switch signals S 11  and S 12  are synchronously generated. The control determiner  16  also transmits the select control signal S 18  and the switch permission signal S 19  to the external audio input switch  17  and the switch time adjuster  15 , respectively. As is different from the first embodiment, the switch signal S 12  is not directly transmitted to the audio encoder  12 . Instead, the switch signal S 12  is held by the switch time adjuster  15 , and after the switch time adjuster  15  receives the switch permission signal S 19 , is transmitted as the timing-adjusted switch signal S 20  to the audio encoder  12 . Here, the control determiner  16  is controlled so that the timings of transmission of the select control signal S 18  and the switch permission signal S 19  are dependent on each other, thereby preventing the output of the audio encoder  12  from being unnatural. For example, the switch permission signal S 19  is transmitted to switch between the encoding schemes of the audio encoder  12  before the select control signal S 18  is transmitted. Alternatively, when the external audio input signal S 14  is in the active mode in accordance with the select control signal S 18 , the switch permission signal S 19  is not transmitted, and after the external audio input signal S 14  stops, the switch permission signal S 19  is transmitted. By such a method, the control determiner  16  can be controlled so that the external audio input signal S 14  does not overlap a period of time during which no sound is present when switching of the encoding schemes is performed. 
         [0036]    While, in the aforementioned example, a method has been described which reduces or prevents interruption of audio of the external audio input signal S 14  by controlling the timings of the select control signal S 18  and the switch permission signal S 19 , the process is not limited by this embodiment. 
       Third Embodiment 
       [0037]      FIG. 3  is a block diagram of a device according to a third embodiment of the present invention. In  FIG. 3 , the reference character  121  indicates a first audio encoder which supports a first encoding scheme, the reference character  122  indicates a second audio encoder which supports a second encoding scheme, and the reference character  18  indicates an audio output switch. The reference character S 121  indicates a control signal which is generated by the switch  14  and is used to activate the first audio encoder  121 , the reference character S 122  indicates a control signal which is generated by the switch  14  and is used to activate the second audio encoder  122 , and the reference character S 123  indicates a select control signal which is generated by the switch  14  and is output to the audio output switch  18 . The reference character S 151  indicates an audio signal which is a mixture of the decoded audio signal S 13  and the external audio input signal S 14  and is transmitted to the first audio encoder  121 , the reference character S 152  indicates an audio signal which is a mixture of the decoded audio signal S 13  and the external audio input signal S 14  and is transmitted to the second audio encoder  122 , the reference character S 21  indicates an audio output signal which is obtained by encoding the audio signal S 151  using the first encoding scheme, and the reference character S 22  indicates an audio output signal which is obtained by encoding the audio signal S 152  using a second encoding scheme. The audio output switch  18  selects one of the two encoded audio output signals S 21  and S 22  in accordance with the select control signal S 123 . 
         [0038]    In the audio mixing/reproducing device of  FIG. 3 , initially, the switch  14  generates the control signals S 121  and S 122 . Next, when it is necessary to switch between the encoding schemes, a decoding switch signal  511  and the select control signal S 123  are synchronously generated. On the other hand, the encoded audio output signals S 21  and S 22  are obtained by encoding the same audio signals S 151  and S 152 , respectively, using different encoding schemes. Therefore, when the encoding scheme of the audio decoder  11  is switched to the other, the encoding scheme of the final output can be switched from the first scheme to the second scheme, or from the second scheme to the first scheme, without a time delay. 
       Fourth Embodiment 
       [0039]      FIG. 4  is a block diagram of a device according to a fourth embodiment of the present invention. In  FIG. 4 , the reference character  19  indicates an audio determiner which determines sound levels of a decoded audio signal S 13  and an external audio input signal S 14 . 
         [0040]    In general, when the encoding scheme of an encoded audio input signal S 1  is switched to another, the sound level of the decoded audio signal S 13  which is the result of decoding of the encoded audio input signal S 1 , or the sound level of the external audio input signal S 14  tends to be sufficiently reduced. 
         [0041]    Therefore, in the audio mixing/reproducing device of  FIG. 4 , the audio determiner  19  measures the sound level of each of the decoded audio signal S 13  and the external audio input signal S 14  in predetermined intervals to calculate an accumulated value in each interval. When the accumulated value of the decoded audio signal S 13  or the external audio input signal S 14  is sufficiently small, the audio determiner  19  determines that it is time to switch the encoding scheme of the encoded audio input signal S 1  to another, and outputs an encoding scheme switch activation signal S 17  to a switch  14 . 
         [0042]    While it has been assumed above that the sound levels of both the decoded audio signal S 13  and the external audio input signal S 14  are determined, the sound level of only one of the decoded audio signal S 13  and the external audio input signal S 14  may be determined. 
       Fifth Embodiment 
       [0043]      FIG. 5  is a block diagram of a device according to a fifth embodiment of the present invention. In  FIG. 5 , the reference character  21  indicates an image decoder, and the reference character  22  indicates an image determiner. The reference character S 3  indicates an encoded image input signal, and the reference character S 4  indicates a decoded image signal. 
         [0044]    In general, when the encoding scheme of an encoded audio input signal S 1  from, for example, a DVD is switched to another, the image signal S 4  which is an output of the image decoder  21  tends to contain no motion, i.e., tends to be a still image. 
         [0045]    Therefore, in the audio mixing/reproducing device of  FIG. 5 , the image determiner  22  measures an image motion amount in the image signal S 4  in predetermined intervals to calculate an accumulated value in each interval. When the accumulated value is sufficiently small, the image determiner  22  determines that it is time to switch the encoding scheme of the encoded audio input signal S 1  to another, and outputs an encoding scheme switch activation signal S 17  to a switch  14 . 
       Sixth Embodiment 
       [0046]      FIG. 6  is a block diagram of a device according to a sixth embodiment of the present invention. In  FIG. 6 , the reference character  23  indicates a sound level adjuster which reduces a sound level at the instant that one encoding scheme is switched to another. The reference character S 23  indicates a fade-out instruction signal which is externally input to the sound level adjuster  23 , and the reference character S 24  indicates an audio signal whose sound level has been adjusted. 
         [0047]    In the audio mixing/reproducing device of  FIG. 6 , the sound level adjuster  23  starts a fade-out process in accordance with the fade-out instruction signal S 23 . At the same time when the fade-out process of the sound level adjuster  23  is completed, the sound level adjuster  23  outputs an encoding scheme switch activation signal S 17  to the switch  14 . As a result, two switch signals S 11  and S 12  are synchronously generated, whereby the encoding schemes of an audio decoder  11  and an audio encoder  12  are switched to the same scheme. At the same time when the encoding scheme switching occurs, the sound level adjuster  23  starts a fade-in process. 
         [0048]    Therefore, it is possible to conceal discontinuation which occurs at the instant that one encoding scheme is switched to another. Moreover, by performing a fade-in process immediately after switching in the audio encoder  12  rather than upon switching in the audio decoder  11 , a period of time during which the output of the external audio input signal S 14  is interrupted can be minimized. 
       Seventh Embodiment 
       [0049]      FIG. 7  is a block diagram of a device according to a seventh embodiment of the present invention. In  FIG. 7 , the reference character  24  indicates an audio output switch which outputs a mixture audio signal S 15  which has not been encoded, without modification, only for a period of time during which one encoding scheme is switched to another. The reference character S 25  indicates an encoded audio signal, and the reference character S 26  indicates a select control signal which is input to the audio output switch  24 . 
         [0050]    In the audio mixing/reproducing device of  FIG. 7 , two switch signals S 11  and S 12  are synchronously generated in accordance with an encoding scheme switch activation signal S 17 , whereby the encoding schemes of an audio decoder  11  and an audio encoder  12  are simultaneously switched to the same scheme. Note that the mixture audio signal S 15  is output without being encoded for a period of time during which the encoding scheme of the audio encoder  12  is switched to another. At the same time when the encoding scheme switching is completed in the audio encoder  12 , the audio output switch  24  is switched to the original audio encoder  12  to output the encoded audio signal S 25 . 
         [0051]    Therefore, when the period of time during which the encoding scheme of the audio encoder  12  is switched to another is long, by temporarily outputting the audio signal S 15  which has not been encoded, it is possible to avoid a silent state. 
       INDUSTRIAL APPLICABILITY 
       [0052]    As described above, the audio mixing/reproducing device of the present invention can output an encoded audio signal which is obtained by mixing with an external audio signal using the same encoding scheme as that of an input. Therefore, the audio mixing/reproducing device of the present invention is useful for real-time mixing and reproduction of an audio signal.