JP2001119636A - Digital television broadcast receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital television broadcast receiver with the configuration of a conventional digital television broadcast reception terminal device, having only one clock recovery means, that is, exhibiting audio and video signals belonging to the same program that can simultaneously exhibit audio and video image signals belonging to other program. SOLUTION: This digital television broadcast receiver is provided with a reception circuit 1, that receives broadcast data, a multiplexer/demultiplexer circuit 2 that demultiplexes compressed audio data and clock data of a 1st program and compressed video data and clock data of a 2nd program from the received broadcast data, a clock recovery circuit 2 being a sole circuit that recovers a reference clock specific to the 1st program from the demultiplexed clock data, an audio decoder 6 that decodes the demultiplexed compressed audio data of the 1st program on the basis of the recovered reference clock and provides an output of audio data, and a video decoder 7 that decodes the demultiplexed compressed video data of the 2nd program asynchronously with the reference clock denoted by the clock of the 2nd program included in the broadcast data and provides an output of the decoded data as video data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital television broadcast receiving apparatus, and more particularly, to a plurality of compressed audio data and compressed video data unique to each program and a plurality of clock data indicating a reference clock for decoding and reproducing the data. The present invention relates to a digital television broadcast receiving apparatus that receives broadcast data multiplexed for the number of programs.

[0002]

2. Description of the Related Art With the increase in the number of channels in digital television broadcasting, the way viewers enjoy is diversifying, and there is a demand for a digital television broadcast receiver capable of simultaneously viewing two different programs. However, there is no digital television broadcast receiving apparatus that enables such a viewing method at present, but as one method for realizing the same, for example, a conventional general digital television broadcast (which can only watch one channel) is used. It is conceivable to add a clock recovery circuit in the receiving device.

[0003] Specifically, a receiving circuit for receiving radio waves,
A demultiplexing circuit that separates information in which a plurality of programs are time-division multiplexed by a packet into a single stream, and a value of a program clock reference (hereinafter, referred to as “PCR”) unique to the selected first program, One clock reproduction circuit for reproducing a system time clock (hereinafter, referred to as “STC”) unique to the first program, which is a reference for achieving time synchronization of signal output, and a PCR for a selected PCR unique to the second program. Another clock reproduction circuit for reproducing the STC unique to the second program, which is a reference for achieving time synchronization of the signal output from the value, and an audio decoder for expanding the compressed audio digital information and decoding it into an audio signal And a video decoder that expands the compressed video digital information and decodes it into a video signal, so that the STC can be reproduced simultaneously for each program. It becomes possible to keep the temporal synchronization between the sender and the receiver, can present a program as intended by the voice and video sender.

[0004]

However, in the above configuration, two clock recovery circuits must be used in order to simultaneously present different programs, which inevitably increases the cost. Therefore, receiving two programs by using one clock recovery circuit as in an existing receiving device,
Although it is desired from the viewpoint of cost, one clock reproducing circuit can reproduce only the STC of one program, and must reproduce the other program asynchronously. In such a case, depending on the program selected for asynchronous reproduction, the contents may not be understood at all and useless reproduction processing may be performed due to the data attribute of the program.

Accordingly, in the present invention, a request for simultaneous reproduction of two programs is issued by displaying a video of a song program broadcast on the second channel from a speaker while displaying an image of a baseball broadcast or the like normally broadcast on the first channel. Paying attention to the point that it is expected to frequently occur when one is video and the other is audio, such as outputting, asynchronous playback of a program that is inferior to synchronous playback even if asynchronous playback is performed, but does not become meaningless,
A program that would be wasted if asynchronous playback is performed is played back by using the STC played back by the clock playback circuit, thereby achieving both a cost requirement and a usage requirement of simultaneous reception of two programs, and is expected to be particularly frequent. In other words, that is, the case where the user listens to the audio of one program and the video of the other program.

[0006]

In order to achieve the above-mentioned object, a digital television broadcast receiving terminal device according to the present invention provides a digital television broadcast receiving terminal for each program which indicates each program data and a reference clock for decoding and reproducing the data. A digital television broadcast receiving apparatus for receiving broadcast data in which clock data is multiplexed, receiving means for receiving broadcast data, a first program in which the program data is compressed audio data, and Separating means for separating a second program comprising data from the received broadcast data;
Clock reproducing means for reproducing a reference clock unique to the first program from clock data included in the program, and decoding the compressed audio data of the first program based on the reproduced reference clock of the first program to reproduce the audio. And a video decoder that decodes the compressed video data of the second program asynchronously with a reference clock included in the second program and outputs the decoded video as video.

[0007]

Embodiments of the present invention will be described below in detail with reference to the drawings. [First Embodiment] FIG. 1 is a functional block diagram of a digital television broadcast receiving terminal device according to a first embodiment of the present invention.

The present digital television broadcast receiving terminal device is
An apparatus for receiving a digital television broadcast in which a plurality of programs are time-division multiplexed by a packet into a single stream in a PEG2 television broadcast. It comprises a circuit 3, an output control unit 4, a storage memory 5, an audio decoder 6, a video decoder 7, an information display unit 8, and a command input unit 9.

The receiving circuit 1 includes a resonance circuit composed of a coil and a capacitor, an amplifier, etc., selects and demodulates a digital modulation signal, and outputs the signal to the demultiplexing / demultiplexing circuit 3. The multiplex signal output from the receiving circuit 1 is a series of fixed-length packets called a transport stream.

The demultiplexing circuit 3 separates and extracts program information from the multiplex-compressed digital signal output from the receiving circuit 1. The output control unit 4 acquires program information from the demultiplexing circuit 3, outputs information to the information display unit 8, receives a command from the command input unit 9, and controls the demultiplexing circuit 3. The storage memory 5 temporarily stores program information received from the output control unit 4.

The information display unit 8 is a monitor that superimposes on a video signal and performs on-screen display. The information display unit 8 displays commands generated by the output control unit 4 in accordance with an operation of selecting audio and video programs in a list format. . FIG. 2 is a program selection screen according to the present embodiment in the information display unit 8. The left column is a channel menu for selecting an output of a video program, and the right column is a channel menu for selecting an output of an audio program. Channels for which output settings have been made are displayed in different colors.

The command input unit 9 is constituted by a remote controller, and is not limited to the same program as in a conventional digital television broadcast receiving apparatus. Is changed, the audio and video channels to be output can be individually selected. When the selection is confirmed, this output request is output to the output control unit 4.

According to the output request received from the command input unit 9, the output control unit 4 reads the packet ID of the requested audio program from the storage memory 5 in order to receive the selected audio program. In the demultiplexing circuit 3,
The setting is made so as to extract the packet of the requested audio compression signal, and to extract the PCR belonging to the audio program in order to reproduce the STC of the audio program.

[0014] With regard to the video, in order to receive the program of the selected video, it is set so that only the packets of the compressed signal of the selected video program are extracted. The demultiplexing circuit 3 separates the compressed audio information packet and the compressed video information packet according to the instruction of the output control unit 4, and sends the compressed audio information to the audio decoder 6. The information is output to the video decoder 7, respectively.

In the case where the audio is output with the time synchronization of the output not being the same, the audio is output intermittently.
Since the sound is unpleasant, if the sound does not almost completely match the intention of the transmitting side, the viewer has a property of immediately giving a sense of incongruity to the viewer. On the other hand, even if the output of the video is slightly out of synchronization, the degree of giving the viewer a sense of discomfort due to the afterimage phenomenon is small. Therefore, in the present embodiment, the decoding accuracy of the audio is prioritized over the decoding accuracy of the video,
Reproduces the STC of only the audio program.

The clock recovery circuit 2 is constituted by a PLL circuit, and extracts a unique discrete PCR value of each program transmitted by an adaptation field in a packet separated by the demultiplexing circuit 3.
Is reproduced to the same STC as before encoding. At this time, if the audio and video to be reproduced are selected as different programs by the command input unit 9, the STC is determined from only the PCR included in the signal of the program to which the audio belongs in consideration of the priority of the decoding accuracy. Reproduce.

The audio decoder 6 expands the compressed audio digital information and decodes it into an audio signal. The decoded audio signal includes a presentation time stamp (hereinafter, “PT”) that defines the audio output timing together with the audio.
S "), and presents an audio when the PTS matches the STC obtained by reproducing from the PCR included in the audio digital information, and synchronizes the time between the transmitting side and the receiving side. I keep it.

The video decoder 7 expands the compressed video digital information and decodes it into a video signal. Here, a detailed configuration of the video decoder 7 will be described with reference to FIG. FIG.
FIG. 3 is a functional block diagram of the video decoder 7 in the first embodiment. The video decoder 7 includes a decoding unit 200
, A buffer 210, a decode control unit 211, a preset subtraction unit 212, a counter 213, and DC-0V
The detection unit 214 is configured.

The buffer 210 is composed of a RAM, and temporarily stores the compressed video digital data sent from the demultiplexing circuit 3. The DC-0V detection unit 214 is a circuit that detects whether or not a video is output. For example, when a video is lost, that is, when a 0 V output that continues for a predetermined time or more is obtained, a video that has not been output to the decode control unit 211 is Send a signal.

When the audio and video to be reproduced are selected as different programs by the command input unit 9, the clock reproducing circuit 2 reproduces the PCR encoded in the program information to which the audio belongs to the STC. Therefore, the PCR included in the program information to which the video belongs cannot be reproduced on the STC. Therefore, the decode control unit 211 does not use the signal reproduced by the clock reproduction circuit 2 and stores the value of the PTS contained in the program information to which the video belongs to the buffer 21.
Obtain from 0.

The preset subtraction unit 212 subtracts from the PTS a value corresponding to the time required for decoding from the value of the PTS obtained by the decode control unit 211, and subtracts this value from the PTS
An initial value is generated as a pseudo STC in place of TC (hereinafter, this processing is referred to as “synchronization processing”). After the generation of the initial value, the counter 213 uses the STC obtained by PCR reproduction from the audio information as a clock input, and increases the initial value of the pseudo STC obtained from the preset subtraction unit 212 as a preset value, thereby increasing the pseudo value. The STC value is updated, and this value is sent to the decoding unit 200.

The reason why the value corresponding to the time required for decoding is subtracted from the value of PTS is that the value of PTS is usually determined on the encoding side at the time when the signal reaches the decoder in consideration of the time required for decoding. If the PTS is generated as the STC as it is because the time is set slightly later than that, the video data having the corresponding PTS cannot be output during decoding at the time when the STC is generated. is there.

As soon as decodable video data is input to the buffer 210, the decoding unit 200 reads and decodes the video data, and decodes the PTS input to the buffer 210.
Is matched with the value of the pseudo STC from the counter 213, the decoded data is D / A converted and output as a video signal. In this embodiment, the following 2
In one case, the above-described synchronization processing is performed.

One is a case where the system time clock and the PTS included in the information are discontinuously changed without notice due to the convenience of the encoding side, and a mismatch between the pseudo STC and the PTS occurs. The other is that the values of STC and PTS are finite values represented by 42 bits and should be reset to 0 or a value close to 0 someday. S
This is a case where mismatch between TC and PTS occurs.

In the above two cases, since data matching the pseudo STC does not exist in the buffer, the data is not consumed and is only stored and overflows. In order to avoid this in advance, a certain threshold is provided, and when the amount of data accumulated in the buffer 210 exceeds this threshold, the pseudo STC value is updated again based on the PTS detected at this time. And synchronization (synchronization processing).

Here, the decoding control unit 211 determines
The reason for setting the threshold value will be described with reference to FIG. FIG. 4 is a diagram illustrating the relationship between the amount of data stored in the buffer 210 and time. Since the stored data is consumed in a certain block unit, the amount of storage is represented in time series. It has a saw-like waveform. The upper limit of the frame in the figure is the main buffer size. If data is taken in beyond this amount, an overflow occurs and the taken-in data is lost.

The main cause of this overflow is the PTS
And STC may be inconsistent.
When the synchronization of C is performed again, the value of the PTS newly incorporated in the buffer 210 is required. At this time, for example, in the drawing, the PTS (t0) corresponding to the information taken in at the time point t0 that exceeds the threshold value is t0
The PTS (t1) corresponding to the information taken at a time t1 when the threshold value is exceeded and the PTS (t1) corresponding to the information taken at a time t1 that exceeds the threshold is taken at a time slightly earlier than the time t1. In rare cases, the location of the PTS may exist either before or after the time when the threshold is exceeded, and the context is not constant.

Therefore, even if an attempt is made to detect the PTS corresponding to the data at this point after the overflow is detected, the PT
There is a possibility that S is included in data that has already been consumed. Therefore, it is necessary to provide a threshold value for determining overflow detection just before the PTS is consumed. In addition to acquiring the value of the PTS, the decode control unit 211 performs detection of an underflow of the buffer 210, detection of an excess of the threshold value, and acquisition of non-output information of a video from the DC-0V detection unit 214. The subsequent output control operation is determined from this information. Note that, even if the buffer 210 detects an underflow or exceeding the threshold value of accumulated data, the buffer 210 reads the value of the PTS corresponding to the data at the time of detection.

Here, the overall operation of each device of the digital television broadcast receiving terminal according to the first embodiment of the present invention will be described. FIG. 5 is a flowchart illustrating the operation of the digital television broadcast receiving terminal device according to the present embodiment. First, when the power of the digital television broadcast receiving terminal device is turned on, the output control unit 4 determines whether or not a channel display request has been issued from the command input unit 9 (step S1). For example, the channel of the program that can be output is displayed on the information display unit 8 for each audio and video on the display (step S2). If the channel display request has not been issued, the process proceeds to the next step.

Next, the output control section 4 determines whether or not a new program output setting has been made from the command input section 9 (step S3). When the output setting of the program is newly performed, the contents of the output setting are stored in the storage memory 5 (step S4). When the output setting of the program is not performed, the process proceeds to the next step. Next, the output control unit 4 determines whether or not the output setting of the program stored in the storage memory 5 is set to another program for audio and video (Step S).
5). If the output settings of the program are different for audio and video, the output control unit 4 separates the audio data and the PCR set for output from the audio program information, and separates the PCR from the video program information. Is given to the demultiplexing circuit 3 without separating the video data, and the demultiplexing circuit 3 performs the demultiplexing in accordance with the instruction (step S9). If the program output setting is the same for audio and video, the process proceeds to the next step.

When the output setting of a program is the same program setting for audio and video, the output control unit 4 demultiplexes the audio data, video data and PCR data of one set program so as to separate them. An instruction is issued to the circuit 3, and the demultiplexing circuit 3 separates according to the instruction (step S6). Next, the clock reproduction circuit 2 executes the PCR of one set program.
To reproduce the STC (step S7), and proceed to the next step.

Next, the audio decoder 6 and the video decoder 7
Outputs audio and video based on the reproduced STC value while maintaining the quality at the time of encoding (step S
8) Return to the first step. Step S10 and subsequent steps, which are lower steps of step 9, will be described. The clock reproduction circuit 2 reproduces the STC from only the PCR of the audio program (step S10), and proceeds to the next step.

Next, the decoding control section 211 in the video decoder 7 determines whether or not the data amount of the buffer 210 does not exceed the threshold value (step S11). When the data amount of the buffer 210 exceeds the threshold, the decode control unit 211 reads the value of the PTS held by the video program from the video data stored in the buffer 210, and the preset subtraction unit 212 Subtracting the value corresponding to the time required for decoding from the value of
Is generated, that is, a synchronization process is performed (step S17), and the process proceeds to step S18. Buffer 21
If the amount of data stored in 0 does not exceed the threshold, the process proceeds to the next step.

Next, the decode control section 211 determines whether or not the data in the buffer 210 has underflowed (step S12). If the data in the buffer 210 has underflowed, a process of temporarily delaying the decoding, which is a general error concealment process, is performed (step S13), and a synchronization process is further performed (step S17), and the process proceeds to step S18. . If no underflow has occurred, go to the next step.

Next, the decoding control section 211 controls the DC-0
It is determined whether a signal of video output interruption has been transmitted from the V detection unit 214 (step S14). When the signal of the video output interruption is transmitted, an error concealment process for replacing the missing frame with the previous frame is performed (step S15), and a synchronization process is further performed (step S1).
7), and proceed to step S18. If the video output suspension signal has not been transmitted, the process proceeds to the next step.

Next, the decode control unit 211 determines whether the output setting has been changed or whether the power has just been turned on (step S16). Whether the output setting has been changed
Alternatively, immediately after the power is turned on, the decode control unit 211
A synchronization process is performed (step S17), and the process proceeds to the next step. Next, the counter 213 reads the PCR from the audio information.
The STC obtained by the reproduction is used as a clock input, the initial value of the pseudo STC obtained from the preset subtraction unit 212 is increased as a preset value, the value of the pseudo STC is updated (step S18), and this value is sent to the decoding unit 200. send.

Next, the audio decoder 6 outputs audio while maintaining the quality at the time of encoding based on the STC reproduced from the PCR possessed by the audio program. On the other hand, the video decoding unit 200 receives the pseudo ST
An image is output based on C (step S19), and the process returns to the first step. The above is the overall operation flow of each device of the digital television broadcast receiving terminal according to the first embodiment of the present invention.

Here, how the data structurally changes until the received data is output as a result of the implementation of the first embodiment according to the present invention will be described. FIG. 6 is a diagram showing the flow of broadcast data from receiving a broadcast to outputting information in the present embodiment. FIG. 6A shows the flow of data reception. The time progresses from the left side to the right side in the figure, and the minimum block unit of the program information called a transport packet is sequentially transmitted. The transport packets are sent continuously, and this flow is called a transport stream. In the digital television broadcasting of the MPEG2 system, a plurality of pieces of program information are multiplexed in this transport stream. In FIG.
The case where a program is sent is described.

[0039] The main data constituting the transport packet include PCR, PTS, audio data and video data. FIG. 6B shows the flow of data output. Arrows indicate the flow of PCR to STC regeneration.
In outputting the audio, the clock reproducing circuit 2 reproduces the STC from the PCR encoded in the channel 1 of the program to which the audio belongs. Since the value of the PCR is not present in all transport packets but is included discretely, the value between the PCR values obtained discretely is complemented between the values so that the value becomes the same as before encoding. An STC in finer time units is reproduced. Based on this STC, the audio decoder 6 outputs an audio signal equivalent to an encoded audio signal.

On the other hand, when outputting the video, the video decoder 7 captures the video data, and when the expansion of the video compression signal is completed, reads the value of the PTS corresponding to the expanded compressed video signal, and reads the PTS of the PTS. Pseudo ST based on value
C is generated and output as a video signal when the PTS indicated in the video data stream matches the pseudo STC. However, for the sake of simplicity, it is not mentioned here that the preset subtraction unit 212 subtracts the value corresponding to the time required for decoding from the value of PTS to generate the initial value of the pseudo STC.

As described above, according to the present embodiment, in the configuration of a normal digital television broadcast receiving terminal device having only one clock recovery circuit, the video decoder 7 generates pseudo STC, As a result, the same audio quality as that of the video before encoding can be secured, and the audio and video belonging to different programs can be presented simultaneously.

Although the command input unit 9 is constituted by a remote controller, the command input unit 9 may be a key or the like directly arranged on the image display unit. In addition, the information display unit 8
Although the monitor is superimposed on the video signal and is displayed on the screen, a remote controller of the command input unit 9 may be provided with a liquid crystal display unit or the like, and the display may be performed on the liquid crystal display unit or the like.

[Second Embodiment] Hereinafter, a second embodiment of the present invention will be described in detail. As in the first embodiment, the second embodiment is an apparatus for receiving digital television broadcasts, which is an MPEG2 television broadcast, in which a plurality of programs are time-division multiplexed into a single stream by packets. A digital television broadcast receiving terminal device having one clock reproducing circuit and capable of arbitrarily selecting a program to be output for each of audio and video.

The difference from the first embodiment will be described with reference to FIG. The difference from the first embodiment is that when the audio and video to be reproduced are selected as different programs by the command input unit 9, the PTS and STC are changed as soon as the video signal arrives from the demultiplexing circuit 3 to the video decoder 7. The video decoder 7 decompresses the compressed video digital information, decodes the compressed video digital information into a video signal, and sequentially outputs the video signal to a video output terminal.

If the audio signal is output sequentially as soon as it can be decoded without using the PTS and STC, the output interval of the audio is not constant and immediately gives a sense of incongruity to the viewer. On the other hand, even if the temporal synchronization of the output is slightly lost, the viewer can be fooled by the afterimage phenomenon, so that the output by the above-described video output method is also possible.

Here, how the data structurally changes by the time the received data is output as a result of the implementation of the second embodiment according to the present invention will be described. FIG. 7 is a diagram showing a data flow from broadcast reception to information output in the present embodiment. As a simple example, channel 1
And the case where two programs of channel 2 are transmitted.

FIG. 7A shows the flow of data reception. Time progresses from left to right in the figure, and blocks of program information called transport packets are sequentially transmitted. FIG. 7 shows the simplest program configuration.
The case where two programs of channel 1 and channel 2 are transmitted is described. FIG. 7B shows the flow of data output.

In this embodiment, the audio output reproduces the STC from the PCR encoded in channel 1 of the program to which the audio belongs. Upon outputting the video, when the video decoder 7 captures the video data, the STC and the PTS of the video signal are not used at all, and the video is immediately decoded and presented when it becomes possible to decode.

At this time, by outputting the PTS of the video signal without using it, when viewed in a minute time unit, the order of the video to be presented is changed, and the time interval to be presented is unstable. However, the transmitting side of the digital television broadcast usually transmits information at a speed close to real time so that the buffering of the receiving side does not cause overflow or underflow, so that the receiving side uses a PTS that defines the presentation time. Even if it is neglected and sequentially decoded and output at the time when it can be decoded on the receiving side, a fatal defect is unlikely to be caused so as to give a viewer a sense of incongruity due to the afterimage phenomenon of human vision.

As described above, according to the present embodiment, in the configuration of the ordinary digital television broadcast receiving terminal device provided with only one clock recovery circuit, the STC of the video signal is
Also, the PTS of the video signal is not used, the video data is taken into the video decoder 7 and immediately decoded and presented when it becomes ready to be decoded, and output as a video signal, so that the same audio quality as before is required. The minimum video quality can be ensured, and audio and video belonging to different programs can be presented simultaneously.

In this embodiment, no error concealment processing for presenting a complete video frame without any omission so as not to give a viewer a sense of incongruity is not described. As in the embodiment of
The error concealment process may be performed together.

[0052]

As is apparent from the above description, the digital television broadcast receiving terminal device according to the present invention is capable of transmitting each program data and clock data for each program indicating a reference clock for decoding and reproducing the data. A digital television broadcast receiving apparatus for receiving multiplexed broadcast data, comprising: a receiving unit for receiving broadcast data; a first program in which program data is composed of compressed audio data; and a first program in which program data is composed of compressed video data. Separation means for separating the second program from the received broadcast data; clock reproduction means for reproducing a reference clock unique to the first program from clock data included in the separated first program; An audio decoder for decoding the compressed audio data of the first program based on the reference clock of the first program and outputting the decoded audio as audio, and a compressed video data of the second program The reference clock included in the second program, characterized in that it comprises a video decoder for outputting as a video decode asynchronously.

Thus, the compressed audio data of the first program is decoded with the same precision as the audio signal before encoding by using the means for reproducing the reference clock, and the compressed video data of the second program is converted to the standard video signal. No clock is used,
The compressed video data is taken into the video decoder, and when it becomes ready to be decoded, it is immediately decoded and presented. That is, by giving priority to audio decoding accuracy over video and ensuring the minimum required video quality, only one clock reproducing means, that is, a normal digital television broadcast receiving terminal that presents audio and video belonging to the same program With the configuration of the device, simultaneous presentation of audio and video belonging to different programs is realized.

The video decoder further comprises output interruption detecting means for detecting that the decoded video is lost for a predetermined time or more,
If the video is missing for a certain period of time or more, a decoding control means may be provided for continuously outputting the video frame reproduced and output immediately before. As a result, it is possible to prevent the video frame from being output with a part thereof being missing or being interrupted, thereby reducing the degree of giving the viewer a sense of discomfort.

Further, the video decoder may decode the compressed video data of the second program using the ticks of the reference clock of the first program reproduced by the clock reproducing means and output the decoded data as video data. As a result, video that has been decoded at the maximum speed of the decoder until then is decoded and output at a fixed time interval, so that a more natural movement can be presented to the viewer. Further, the degree of occurrence of buffer underflow is further reduced.

The broadcast data includes, for each program, time stamp data representing the timing for decoding the compressed audio data and the compressed video data by the count value of the reference clock. The time stamp data of the second program is separated together with the compressed video data, and the video decoder sets the time stamp included in the time stamp data of the second program separated by the separating means as a preset value and indicates a reference clock of the first program. It may include a counter that counts up the pulse train as a clock input, and a decoding unit that decodes the compressed video data based on the value of the counter and outputs the decoded video data as video data.

Thus, the video decoder receives the value of PTS included in the program information to which the video belongs, and
From the value of TS, PT
The value is subtracted from S, and this value is newly generated as a pseudo STC instead of the previous STC, so that the PTS value and the STC value can be synchronized. By presenting a video when the pseudo STC and the PTS indicated in the video stream match, substantially the same effect as when video is output using a regular STC is obtained, and Time synchronization with the receiving side is almost maintained.

Further, the video decoder further detects a buffer memory for temporarily storing the compressed video data of the second program separated by the separating means, and a buffer abnormality in which the storage state of the buffer memory overflows or underflows. A buffer abnormality detecting unit, and a preset value updating unit that updates a preset value of the counter with a time stamp included in the time stamp data of the second program each time a buffer abnormality or loss of video output for a predetermined time or more is detected. You may have.

Thus, the interruption of the video output caused by the mismatch between the pseudo STC and the PTS, which occurs when the value of the PTS is reset on the encoding side, etc. Output normalization can be performed early.

[Brief description of the drawings]

FIG. 1 is a functional block diagram of a digital television broadcast receiving apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a list screen displayed for selecting an audio and a video signal in an information display unit according to the first embodiment of the present invention.

FIG. 3 is a functional block diagram of a video decoder according to the first embodiment of the present invention.

FIG. 4 is a diagram illustrating a relationship between an amount of data accumulated in a buffer and time according to the first embodiment of the present invention.

FIG. 5 is a flowchart showing an operation procedure in the first embodiment according to the present invention.

FIG. 6A shows a flow of data reception in the first embodiment according to the present invention. (B) shows the flow of data output in the first embodiment according to the present invention.

FIG. 7A shows a flow of data reception in a second embodiment according to the present invention. (B) shows a flow of data output in the second embodiment according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Receiving circuit 2 Clock regeneration circuit 3 Demultiplexing circuit 4 Output control unit 5 Storage memory 6 Audio decoder 7, 207 Video decoder 8 Information display unit 9 Command input unit 200 Decoding unit 201 Buffer 211 Decode control unit 212 Preset subtraction unit 213 Counter 214 DC-0V detector 215 Decode manager

Claims (5)

[Claims] 1. A digital television broadcast receiving apparatus for receiving broadcast data in which each program data and clock data for each program indicating a reference clock for decoding and reproducing the program data are multiplexed. Receiving means for receiving broadcast data; and separating means for separating a first program whose program data is composed of compressed audio data and a second program whose program data is composed of compressed video data from the received broadcast data. A clock reproducing means for reproducing a reference clock unique to the first program from clock data included in one program, based on the reproduced reference clock of the first program,
An audio decoder for decoding the compressed audio data of the first program and outputting it as audio; a video decoder for decoding the compressed video data of the second program asynchronously with a reference clock included in the second program and outputting the decoded video as video. A digital television broadcast receiving device comprising: 2. The video decoder according to claim 1, wherein said video decoder detects output loss of the decoded video for a predetermined time or more, and when the video is missing for a predetermined time or more, the video decoder reproduces and outputs the video immediately before. 2. The digital television broadcast receiving apparatus according to claim 1, further comprising: decode control means for continuously outputting a video frame. 3. The video decoder according to claim 1, wherein the video decoder decodes the compressed video data of the second program by using the reference clock of the first program reproduced by the clock reproducing means and outputs the decoded video data as video data. The digital television broadcast receiving device according to claim 2, wherein 4. The broadcast data includes, for each program, time stamp data representing the timing of decoding the compressed audio data and the compressed video data by the count value of the reference clock. Separating the time stamp data of the second program together with the compressed video data of the second program, the video decoder sets a time stamp included in the time stamp data of the second program separated by the separating means as a preset value, A counter that counts up a pulse train indicating a reference clock of the first program as a clock input; and a decoding unit that decodes the compressed video data based on a value of the counter and outputs the compressed video data as video data. The digital television broadcast receiving apparatus according to claim 3. 5. The video decoder further comprises: a buffer memory for temporarily storing the compressed video data of the second program separated by the separation means; and a buffer error in which the storage state of the buffer memory becomes overflow or underflow. A buffer abnormality detecting unit for detecting the buffer abnormality, or updating the preset value of the counter with a time stamp included in the time stamp data of the second program each time a buffer abnormality or loss of video output for a predetermined time or more is detected. The digital television broadcast receiving device according to claim 4, further comprising a preset value updating unit.