Apparatus for reproducing and decoding multiplexed data from a record medium with means for controlling data decoding as a function of synch

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RELATED APPLICATIONS

U.S. patent application Ser. No. 07/925,736, filed Aug. 7, 1992 now U.S. Pat. No. 5,291,486.

BACKGROUND OF THE INVENTION

This invention relates to apparatus for reproducing multiplexed data from a record medium, such as time division multiplexed video and audio data recorded on an optical disk, and more particularly, to such apparatus which senses synchronization errors and controls video and audio decoding as a function of those errors.

It has been proposed to record digital video and audio data in a time division multiplexed format in successive tracks on a record medium, such as successive circular tracks on an optical disk. The multiplexed data is arranged in a pack, such as in accordance with a suggested standard (ISO1172) of the Motion Pictures Experts Group (MPEG), and as schematically illustrated in FIG. 7, one or more packs are recorded in a track. A pack is comprised of a pack header followed by a video packet and an audio packet. The pack header includes a PACK START CODE which, preferably, is in the form of a unique bit pattern which identifies the beginning of the pack header. A system clock reference SCR follows the PACK START CODE and represents a time code corresponding to the time at which the pack was recorded. The time code may represent real time (hours, minutes, seconds, etc.) or may be a multi-bit number derived from a system clock that was turned on when the information on the record medium was recorded. For example, the time at which the last byte in the preceding pack was recorded on the record medium may be represented by system clock reference SCR.

The pack header also includes MUX RATE data representing a transfer rate, that is, the rate at which video and audio data included in the video and audio packets, respectively, are time division multiplexed.

The video packet includes a packet header followed by encoded digital video data. The video packet header is comprised of a VIDEO PACKET START CODE whose function is similar to that of the aforementioned PACK START CODE, namely to identify the beginning of the video packet. It is appreciated that the VIDEO PACKET START CODE thus is formed of a unique bit pattern that may be easily recognized. Following the VIDEO PACKET START CODE is a video decoding time stamp (DTSV) which is a multi-bit number that identifies the time at which a video decoder initiates its operation to decode the video data. As will be described below, in a proposed reproducing device, the video and audio data are demultiplexed from the pack illustrated in FIG. 7, and supplied to respective video and audio decoders. It is important that each decoder be supplied with a START signal that coincides with the beginning of the video and audio data, respectively, thereby assuring that the video decoder properly decodes the video data and that the audio decoder properly decodes the audio data. The video decoding time stamp DTSV is referenced to the system clock reference SCR, the latter being used to preset a clock which, when incremented to a value equal to the video decoding time stamp DTSV, essentially turns on the video decoder.

The audio packet is similar to the video packet and includes encoded digital audio data which is preceded by a packet header. Like the video packet header, the audio packet header includes an AUDIO PACKET START CODE which, when detected, identifies the beginning of the audio packet, followed by an audio decoding time stamp DTSA which represents the time at which the audio decoder is to be turned on to decode the audio data. Like the video decoding time stamp DTSV, the audio decoding time stamp DTSA is referenced to the system clock reference SCR.

One example of apparatus which has been proposed to reproduce the multiplexed video and audio data exhibiting the format shown in FIG. 7 is illustrated in FIGS. 6A and 6B. Assuming that the multiplexed data is recorded on an optical disk, the reproducing apparatus is comprised of a disk drive 1, a demodulator 2, an error correcting code (ECC) circuit 3, a ring buffer 4, a demultiplexer 5 and, as shown in FIG. 6B, separate video and audio decoding channels, each being comprised of a buffer and a decoder. Disk drive 1 is conventional and includes a pickup head which reproduces the data packs having the format shown in FIG. 7 and supplies same to demodulator 2 which demodulates the multiplexed data therefrom. This demodulated digital data is supplied to ECC circuit 3 which, as is conventional, detects the presence of errors and, based upon known algorithms, corrects those errors provided, of course, that such errors are not so pervasive as to be uncorrectable. The error corrected digital data then is supplied to ring buffer 4 which stores such data until a predetermined amount is accumulated, whereupon the buffer supplies the stored data to demultiplexer 5. The ring buffer thus provides a buffering action to the operation of the ECC circuit, which may be variable, thereby supplying a substantially steady stream of data to demultiplexer 5.

The demultiplexer includes a data separator 21, a video decoding time stamp register 22, an audio decoding time stamp register 24, a clock register 26 and comparators 23 and 25. Data separator 21 acts to separate the encoded video data, the encoded audio data, the system clock reference SCR, the video decoding time stamp DTSV and the audio decoding time stamp DTSA from the multiplexed bit stream supplied thereto by ring buffer 4. The separated video data is supplied to and temporarily stored in video buffer 6 and, similarly, the separated audio data is supplied to and temporarily stored in audio buffer 8.

Clock register 26 is preset by the separated system clock reference SCR and is coupled to a clock generator 27 which, in accordance with the MPEG standard, generates a 90 KHz clock signal. Clock register 26 thus is incremented from its preset count by each clock signal generated by clock generator 27, thereby producing timing data referred to as system time clock values STC. The system time clock STC is coupled in common to comparators 23 and 25. Video decoding time stamp register 22 receives and stores the separated video decoding time stamp DTSV and supplies this video decoding time stamp to comparator 23. When the system time clock STC is incremented to a count equal to the video decoding time stamp DTSV (STC=DTSV), comparator 23 generates a video decoding start signal. Similarly, audio decoding time stamp register 24 receives and stores the separated audio decoding time stamp DTSA. This stored audio decoding time stamp is supplied to comparator 25; and when the system time clock STC is incremented to a count that is equal to the audio decoding time stamp DTSA (STC=DTSA), comparator 25 generates an audio decoding start signal.

Video buffer 6 (FIG. 6B) preferably is in the form of a first-in first-out (FIFO) memory and supplies separated video data to video decoder 7. When comparator 23 produces the video decoding start signal, the video decoder begins to decode the video data temporarily stored in video buffer 8.

Similarly, audio buffer 8 may be a FIFO memory; and supplies the audio data separated by data separator 21 to audio decoder 9. When comparator 25 produces the audio decoding start signal, the audio decoder is enabled to begin decoding the audio data temporarily stored in audio buffer 8.

FIG. 6A also illustrates a control circuit 28, which may be a central processing unit, coupled to data separator 21 to supply various control command signals thereto. Control circuit 28 responds to operator-generated input signals produced by an input section 29 for controlling the overall operation of the data reproducing apparatus. For example, an operator may activate input section 29 to produce those signals that are typical in optical disk drive devices, such as play, stop, pause, skip, etc. FIG. 6A illustrates that input section 29 also is coupled to disk drive 1 so as to supply such operator-generated input signals thereto.

FIG. 8 is a schematic timing diagram of the timing relationship between the operation of data separator 21 and the video and audio decoders 7 and 9. Let it be assumed that a PLAY signal is produced by input section 29, whereupon control circuit 28 supplies a demultiplexing instruction to data separator 21. Let it be further assumed that data separator 21 begins its demultiplexing operation at time t.sub.1 (FIG. 8) and, for convenience, this time t.sub.1 may be equal to the system clock reference SCR. Accordingly, clock register 26 is preset with this clock value t.sub.1. Line A in FIG. 8 illustrates the video data being written into video buffer 6; and it is appreciated that the slope of line A corresponds to the transfer rate at which such video data is written therein. Time t.sub.2 represents the video decoding time stamp DTSV. Hence, when clock register 26 is incremented from clock value t.sub.1 to clock value t.sub.2, comparator 23 supplies the video decoding start signal to video decoder 7, whereupon a unit of video data which had been temporarily stored in video buffer 6 is decoded. As shown in FIG. 8, this unit is equal to one video frame, or one video picture.

In FIG. 8, line B, which is a discontinuous line, represents the video data which is read from video buffer 6 and decoded by video decoder 7. FIG. 8 also illustrates the capacity of video buffer 6. It will be recognized that buffer overflow may occur if the rate at which video data is read from video buffer 6 is too slow, that is, it is less than the rate at which video data is written therein. Conversely, buffer underflow may occur if the contents of the video buffer are read out before a new frame is written therein. The shaded area beneath line A schematically illustrates the amount of video data remaining in video buffer 6.

Video decoder 7 produces a vertical synchronizing signal when a complete frame of video data has been decoded. If the video decoder is coupled to a suitable video display, a delay is imparted (VIDEO DECODE DELAY) to the decoded video signal prior to its display. This delayed relationship also is illustrated in FIG. 8.

It will be appreciated that the timing relationship depicted in FIG. 8 and described above in connection with the video decoding channel is equally applicable to the audio decoding channel. However, the timing relationship, referred to herein as the synchronization relationship, between video decoder 7 and audio decoder 9 is dependent upon the presetting of clock register 26 by the system clock reference SCR and the incrementing of the clock register to system clock values that are equal to the video and audio decoding time stamps, respectively. But, since the video and audio decoding time stamps are separated by data separator 21, any variations in the synchronization relationship between the video and audio data that might occur in or be attributed to the video and audio buffers will go undetected. One example of a synchronization error that may occur in the apparatus shown in FIGS. 6A and 6B and that will not be detected and, thus, not corrected, now will be described.

Let it be assumed that the data which is reproduced from the disk drive exhibits a high error rate such that ECC circuit 3 is unable to correct such errors. Referring to FIG. 9A, let it be assumed that successive picture intervals reproduced from the optical disk are pictures P12, B11, P14, B13, I1, B0, P3 and B2, wherein the numeral represents the picture interval and the letter represents the usual MPEG characterizations, namely I refers to an intraframe encoded video picture, P refers to a forward predictive encoded video picture and B refers to a bidirectionally predictive encoded video picture. Assuming no uncorrectable errors, video decoder 7 decodes the video data included in the successive picture intervals supplied thereto and rearranges the decoded data in the proper picture sequence shown in FIG. 9B. Consistent with the MPEG standard, a group of pictures (GOP) is comprised of fourteen pictures, or picture intervals, and the number of the first picture included in a GOP is reset to 0.

Let it be assumed that an uncorrectable error occurs in reproduced picture interval P14, as shown in FIG. 9C. For example, video packet header information may be lost. Since video decoder 7 cannot decode video picture P14, the video decoder simply skips this picture and, as shown in FIG. 9D, decodes picture intervals P12, B11, B13, I1, B0, P3 and B2 as if picture P14 never was present. Consequently, the output of the video decoder appears as shown in FIG. 9E. However, when FIG. 9E is compared to FIG. 9B, it is seen that the decoded picture sequence is advanced by one picture interval when an error which prevents the decoding of picture P14 is present. But, since a similar error was not present in the audio data, audio decoder 9 does not similarly advance the units of audio data decoded thereby. Hence, the decoded video and audio data now exhibit loss of synchronization therebetween.

Because data separator 21 operates to separate the video and audio decoding time stamps from the multiplexed data supplied by ring buffer 4, it is structurally difficult to reestablish synchronization between the video and audio data supplied to video and audio buffers 6 and 8 from data separator 21 when, as described above, a unit of video data is lost but a unit of audio data is not. Accordingly, to reestablish synchronization between the video and audio data in the presence of the aforementioned error requires relatively complicated processing downstream of the video and audio buffers.

Another example of a condition which requires resynchronization is described with reference to a "pause" operation, the timing relationship of which is illustrated in FIGS. 10A-10C. In the absence of errors, and during a normal play operation, video and audio data are decoded and displayed in the manner shown in FIG. 10A. As before, a unit of video data corresponds to a video picture, or picture interval, and a unit of audio data is comprised of a predetermined number of samples of the audio information (as one example, 512 samples comprise one unit of audio data). It is clearly seen that the length of one unit of video data is greater than the length of one unit of audio data. Moreover, there is no integral multiple relationship between the length of a unit of video data and the length of a unit of audio data (L.sub.v .perspectiveto.nL.sub.A, where L.sub.v is the length of a unit of video data, L.sub.A is the length of a unit of audio data and is an integral number). As is apparent from FIG. 10A, the synchronization relationship between the video and audio data thus varies continually. However, and with reference to an arbitrary picture interval, FIG. 10A illustrates a time difference t.sub.d between the beginning of picture interval P14 and the beginning of unit A10 of audio data.

Let it be assumed that the user of the reproducing apparatus shown in FIGS. 6A and 6B initiates a pause operation during the time that picture interval B13 is displayed, as illustrated in FIG. 10B. As a result of this pause operation, picture interval B13 is repeatedly displayed. Audio decoder 9 decodes units A7, A8 and A9 of audio data; but since unit A10 accompanies picture interval P14 and since picture P14 is not decoded and displayed, a muting condition exists after unit A9 of audio data is decoded. This muting condition also is illustrated in FIG. 10B and coincides with the repeated display of picture B13.

When the pause operation ends, as shown in FIG. 10C, the next picture interval P14 is displayed; and at a time t.sub.d following the beginning of picture interval P14, the next unit A10 of audio data is decoded. For proper synchronization between the video and audio data, decoding of unit A10 must begin at the delayed time t.sub.d following the beginning of picture P14.

However, in the reproducing apparatus shown in FIGS. 6A and 6B, picture interval P14 and unit A10 of audio data are separated early on from the multiplexed data reproduced from the optical disk and, likewise, the video and audio decoding time stamps are stored early on in registers 22 and 24. With the separated video picture P14 stored in video buffer 6, the separated unit A10 of audio data stored in audio buffer 8, the video decoding time stamp DTSV stored in register 22 and the audio decoding time stamp DTSA stored in register 24, the time difference t.sub.d between the beginning of video picture P14 and unit A10 of audio data is quite difficult to detect. Hence, and since this delay t.sub.d is variable, as discussed above, it is difficult to restore proper synchronization to the video and audio data at the conclusion of a pause operation.

Another drawback associated with the apparatus shown in FIGS. 6A and 6B occurs when disk drive 1 operates to re-read data from, for example, a particular sector because a high error rate has prevented the originally read data from being properly interpreted. For instance, if the disk drive is subjected to shock, vibration or mechanical interference whereby data which is read from a portion of the disk appears as an uncorrectable error, control circuit 28 may, in response to this uncorrectable error, command the disk drive to re-read the same portion of the record medium. Typically, such re-reading results in corrected data which then may be accurately decoded. For example, if the disk drive is a CD-ROM, up to a maximum of 300 milliseconds may be required to access and re-read the same portion of the disk. But, during the re-read operation, the supply of new video and audio data to video and audio buffers 6 and 8 is interrupted. Nevertheless, the data that had been stored previously therein is decoded. As a consequence, the contents of ring buffer 4, video buffer 6 and audio buffer 8 may be exhausted before new data is supplied thereto. This underflow condition may result in noticeable interruptions in the displayed video picture and audio sound; and constitutes a drawback that desirably should be avoided.

OBJECTS OF THE INVENTION

Therefore, it is an object of the present invention to provide data reproducing apparatus which avoids the aforenoted drawbacks, disadvantages and defects of other proposals.

Another object of this invention is to provide data reproducing apparatus which reproduces multiplexed video and audio data and detects and corrects synchronization errors that may be present therebetween.

A further object of this invention is to provide apparatus of the aforenoted type which facilitates the recovery of proper synchronization between reproduced video and audio data at the conclusion of a pause operation.

An additional object of this invention is to provide apparatus of the aforenoted type which avoids the occurrence of an underflow condition in the event that data is re-read from a portion of a record medium.

Still another object of this invention is to provide apparatus of the aforenoted type which selectively provides a wait or a skip operation in the decoding of video pictures in the event of a detected loss of synchronization.

Another object of this invention is to provide apparatus of the aforenoted type in which re-synchronization following a pause operation and following a re-read operation are carried out in similar fashion.

Various other objects, advantages and features of the present invention will become readily apparent from the ensuing detailed description, and the novel features will be particularly pointed out in the appended claims.

SUMMARY OF THE INVENTION

In accordance with this invention, apparatus is provided for reproducing video data from a record medium on which is recorded, in multiplexed form, the video data, reference time data representing a reference time, and video time data representing the time at which decoding of the video data reproduced from the record medium should begin. The reference time data is separated from the multiplexed data and used to generate timing data. The video data and video time data which are reproduced from the record medium are stored in a video buffer, and the video time data in that buffer is extracted. The buffer is connected to a video decoder which decodes the video data temporarily stored in the buffer; and the operation of the video decoder is controlled as a function of a comparison between the generated timing data and the extracted video time data.

As a feature of this invention, decoding of the video data is initiated when the generated timing data is substantially equal to the extracted video time data. A synchronizing error is indicated when the generated timing data and the extracted video time data differ from each other by at least a predetermined amount. As an aspect of this invention, if the extracted video time data exceeds the generated timing data by at least this amount, the decoding of video data by the video decoder is delayed by a picture interval, that is, the video decoder is caused to wait. Conversely, if the generated timing data exceeds the extracted video time data by at least the aforementioned predetermined amount, the video decoder skips to the next video picture to carry out a decoding operation thereon.

As another feature of this invention, the multiplexed data recorded on the record medium also includes audio data and audio time data representing the time at which decoding of the reproduced audio data should begin. The apparatus further includes an audio buffer for temporarily storing the audio data and audio time data which are reproduced from the record medium, an audio time data extractor for extracting the audio time data from the reproduced audio data, and an audio decoder for decoding the reproduced audio data temporarily stored in the audio buffer, the audio decoder being controlled as a function of a comparison between the generated timing data and the extracted audio time data.

As yet another feature of this invention, an interrupt command may be generated to temporarily interrupt the reproduction of new multiplexed data from the record medium. The video decoder responds to the interrupt command to delay until the interrupt command terminates the decoding of the next picture interval of video data. As an aspect of this feature, the timing data is frozen for the duration of the interrupt command and the decoder is inhibited from decoding the video data of the next picture interval when the extracted video time data is greater than the frozen timing data. The generation of timing data resumes when the interrupt command terminates; and once the timing data exceeds the extracted video time data, the video decoder then decodes the next picture interval.

As yet another feature of this invention, a re-read command may be generated to cause a portion of the record medium to be re-read and, concurrently, to cause the video decoder to delay the decoding of video data in the video buffer until the re-read video data is supplied thereto. As an aspect of this feature, the timing data is frozen until the re-read video data is supplied to the video buffer; and the video decoder is inhibited from decoding video data when the extracted video time data is greater than the frozen timing data. The generation of timing data is resumed when the re-read data is supplied to the video buffer; and the video decoder is enabled when the generated timing data exceeds the extracted video time data.

A significant feature of the present invention is the connection of the video time data extractor to the output of the video buffer such that the video time data is extracted immediately upstream of the video decoder. Similarly, the audio time data extractor is connected to the output of the audio buffer such that audio time data is extracted immediately upstream of the audio decoder. Consequently, synchronization errors may be detected easily and accurately. This also permits the ready detection of an overflow or underflow condition of the video buffer merely by comparing the extracted video time data with the generated timing data. Likewise, the presence of an overflow or underflow condition of the audio buffer may be easily detected simply by comparing the extracted audio time data with the generated time data. Furthermore, synchronization between the video and audio data may be determined simply by comparing the extracted video time data with the extracted audio time data.

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 understood in conjunction with the accompanying drawings in which:

FIGS. 1, 1A and 1B comprise a block diagram of data reproducing apparatus which incorporates the present invention;

FIG. 2 is a schematic illustration of the structure of the data stored in audio buffer 8A of FIG. 1B;

FIGS. 3A-3F are timing diagrams which are useful in understanding the advantages derived from the present invention;

FIGS. 4, 4A and 4B comprise a block diagram of data reproducing apparatus similar to that shown in FIGS. 1, 1A and 1B, but with certain modifications thereto;

FIGS. 5A-5D are timing diagrams which are useful in understanding the advantages derived from the present invention as incorporated into the embodiment of FIGS. 4A and 4B;

FIGS. 6, 6A and 6B are a block diagram of data reproducing apparatus heretofore proposed;

FIG. 7 is a schematic representation of the multiplexed data format of the data reproduced in the apparatus of FIGS. 1, 4 and 6;

FIG. 8 is a schematic representation of timing relationships which are useful in understanding the manner in which the data reproducing apparatus of FIGS. 6, 6A and 6B operates; and

FIGS. 9A-9E and 10A-10C are timing diagrams which are useful in explaining the drawbacks and disadvantages associated with the data reproducing apparatus of FIGS. 6, 6A and 6B.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference numerals are used throughout, FIGS. 1A and 1B, when arranged as shown in FIG. 1, comprise a block diagram illustrative of data reproducing apparatus in which the present invention finds ready application. It will be appreciated that the data reproducing apparatus shown in FIGS. 1A and 1B is quite similar to that shown in FIGS. 6A and 6B; and for convenience and simplification, and in an effort to avoid unnecessary duplication, only those differences between the apparatus previously described with respect to FIGS. 6A and 6B and the apparatus now described in connection with FIGS. 1A and 1B will be explained. Demultiplexer 5A in FIG. 1A differs from demultiplexer 5 in FIG. 6A in that demultiplexer 5A does not include video decoding time stamp register 22, audio decoding time stamp register 24 or comparators 23 and 25. Rather, demultiplexer 5A includes a data separator 21A which, as opposed to data separator 21, does not separate video decoding time stamp data DTSV from the encoded video data. For a reason discussed below, data separator 21A demultiplexes the audio data and the audio decoding time stamp data DTSA but, as will be discussed, the demultiplexed audio data and audio decoding time stamp data are stored in an audio buffer 8A (FIG. 1B) in a manner which, nevertheless, retains the timing relationship therebetween.

Data separator 21A also separates the system clock reference SCR which is used to preset clock register 26, the latter being incremented in response to a 90 KHz clock signal generated by clock generator 27 to generate the timing data STC of the system time clock.

Video buffer 6A of FIG. 1B is similar to aforedescribed video buffer 6 and is coupled to data separator 21A to receive therefrom the video data and the video decoding time stamp data DTSV in their time division multiplexed form (as shown in FIG. 7). The output of the video buffer is coupled to a video decoding time stamp extractor 30 which is adapted to extract from the multiplexed video data temporarily stored in video buffer 6A the video decoding time stamp data DTSV. The video buffer also is connected to video decoder 7 to supply to the video decoder the video data from which the video decoding time stamp data has been extracted. Thus, and contrary to the previously proposed apparatus shown in FIGS. 6A and 6B, the video decoding time stamp data and the video data are stored together in video buffer 6A, thus preserving their synchronizing relationship, and the video decoding time stamp data DTSV is not extracted until the video data is supplied to video decoder 7.

A synchronization control circuit 31 (FIG. 1B) is coupled to clock register 26 to receive therefrom the timing data generated by the clock register as the preset count therein is incremented in response to the 90 KHz clock signals supplied by clock generator 27. The synchronization control circuit also is coupled to video decoding time stamp extractor 30 and, as one example, may include coincidence detectors to detect when the timing data generated by the clock register has been incremented to be equal to the extracted video decoding time stamp data DTSV. As will be described, synchronization control circuit 31 also is adapted to determine when the extracted video decoding time stamp data exceeds the generated timing data (DTSV>STC) and also to determine when the generated timing data is greater than the extracted video decoding time stamp data (STC>DTSV). A control signal is supplied from the synchronization control circuit to video decoder 7 to control the operation of the video decoder in response to the detected synchronization relationship of the video data, that is, and as one example thereof, the operation of the video decoder is controlled as a function of the relationship between the generated timing data STC and the extracted video decoding time stamp data DTSV.

Data separator 21A demultiplexes the audio decoding time stamp data DTSA from the audio data which are supplied thereto in an audio packet from ring buffer 4 for the reason now to be described. As mentioned above, the construction of the reproduced video and audio data is, as shown in FIG. 7, established by the MPEG standard. In accordance with this standard, it is possible that the bit pattern of the AUDIO PACKET START CODE included in the audio packet header may appear as actual information data. Consequently, if the audio data and the audio decoding time stamp data DTSA are maintained in their multiplexed form in audio buffer 8A, there is the possibility that actual information may be misinterpreted as an AUDIO PACKET START CODE, thereby introducing errors into the AUDIO PACKET START CODE detection operation. As a result, the audio decoding time stamp data DTSA, whose detection is dependent upon proper detection of the AUDIO PACKET START CODE, may not be sensed. Therefore, to avoid this possibility, data separator 21A operates as a time division demultiplexer for the audio data, thereby assuring proper separation and detection of the audio decoding time stamp data DTSA. As is seen from FIGS. 1A and 1B, the separated audio data and audio decoding time stamp data DTSA are supplied to separate inputs of audio buffer 8A; and as will now be explained with reference to FIG. 2, the synchronization relationship between the audio data and the audio decoding time stamp data DTSA nevertheless is maintained in audio buffer 8A, notwithstanding this separation.

As seen in FIG. 2, the audio information stored in audio buffer 8A (as used herein, the expression "audio information" means both the separated audio data and the audio decoding time stamp data DTSA) is identified by a flag bit. In particular, this flag bit is affixed to each audio information character (such as an audio information byte) and identifies audio data when the flag bit is reset to "0" and audio decoding time stamp data DTSA when the flag bit is set to "1". Thus, even though data separator 21A has demultiplexed the audio decoding time stamp data and the audio data, such demultiplexed audio information nevertheless is stored in audio buffer 8A with their original timing relationship, as represented by the flag bits of the audio information characters shown in FIG. 2. Hence, both audio buffer 8A and aforedescribed video buffer 6A maintain the synchronization relationship of the audio and video data respectively stored therein by reason of the fact that these buffers also store the audio and video decoding time stamp data of their respective audio and video packets.

Audio buffer 8A is similar to aforedescribed audio buffer 6 and is connected to audio decoding time stamp extractor 32 which is adapted to extract from the contents of the audio buffer the audio decoding time stamp data DTSA. The audio buffer also is connected to audio decoder 9 to supply thereto the temporarily stored audio data for decoding. It is appreciated that, in the reproducing apparatus shown in FIGS. 1A and 1B, the audio decoding time stamp data DTSA is maintained with the audio data until the audio data is supplied to audio decoder 9, thereby maintaining the synchronization relationship of the audio data.

The extracted audio decoding time stamp data DTSA is supplied by extractor 32 to synchronization control circuit 31 for comparison with the timing data STC generated by clock register 26. The synchronization control circuit senses when the timing data has been incremented to a value equal to the extracted audio decoding time stamp data (STC=DTSA), and also senses when the audio decoding time stamp data DTSA is greater than the timing data (DTSA>STC) and when the timing data is greater than the audio decoding time stamp data (STC>DTSA). The operation of audio decoder 9 is controlled as a function of this detected synchronization relationship, that is, the relationship between the timing data STC and the extracted audio decoding time stamp data DTSA. In addition, synchronization control circuit 31 functions to compare the value of the extracted video decoding time stamp data to the value of the extracted audio decoding time stamp data for the purpose of detecting and correcting a synchronization error between the video and audio decoders.

The manner in which the reproducing apparatus illustrated in FIGS. 1A and 1B operates now will be described with reference to FIGS. 3A-3F. Let it be assumed that video and audio data are recorded on a record medium, such as an optical disk, in the MPEG format shown in FIG. 7. Let it be further assumed that the recorded video data represents successive picture intervals P12, B11, P14, B13, I1, B0, P3 and B2, as illustrated in FIG. 3A. It is further assumed that the video decoding time