JP3350365B2 - Video synchronization signal correction device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to video synchronization signal correcting device, video sync used specifically by the relay device such as a video output device of the broadcasting station Tsu had to re-receive and transmit digital video bit stream The present invention relates to a signal correction device.

[0002]

2. Description of the Related Art In recent years, with the development of digital encoding technology of video and audio and broadband network technology,
The development of applications using these has become active. Among them, a digital broadcasting system represented by a digital CATV or the like is considered as one of the promising applications.

In a digital broadcasting system, a plurality of video transmitting devices are used on a broadcasting station side, and a video signal photographed by a camera or the like is output from the transmitting devices by an MPEG.
The video stream is transmitted to the video output device as a video stream such as two streams. In this video output device, a relay process is performed in which one of a plurality of received video streams is selected and retransmitted to a subscriber via a network.

In this case, since the video synchronization signal in each of the plurality of video transmission devices is generated based on a separate clock for each of the transmission devices, a plurality of video synchronization signals having different timings are supplied to the video output device. A stream will be sent. Therefore, when streams transmitted from a plurality of transmission devices having different timings of the video synchronization signal are switched and retransmitted on the way by the video output device, the subscriber, that is, the receiving side, has a discontinuity in the video synchronization signal. This causes a problem that, for example, the display / reproduction screen is disturbed.

Further, if there is a clock deviation between the clock of the video transmission device and the clock of the video output device, the clock deviation is accumulated with time. Therefore, if the video output device performs synchronization processing for synchronizing the video stream from the video transmission device with the synchronization signal of the video output device, overflow / underflow of the video frame will eventually occur in the video output device. Become.

[0006]

As described above, since the video synchronizing signal in each of the plurality of video transmitting devices is generated based on a separate clock for each of the transmitting devices, a plurality of video synchronizing signals having different timings are provided. If the stream transmitted from the sending device is switched and retransmitted in the middle by the video output device, there is a problem that a discontinuity of the video synchronization signal occurs on the receiving side. In addition, since the value of the clock deviation between the clock of the video transmission device and the clock of the video output device is accumulated with time and increases, the video deviation from the video transmission device is synchronized with the synchronization signal of the video output device. When the synchronous processing is performed, there arises a problem that a video frame overflows / underflows in the video output device.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has been made in order to correct the transmission timing so that each video bit stream having a different video synchronization signal timing becomes a stream created by the same video synchronization signal. ,
Stream switching at the time of retransmission, and to provide the possibility and to that sync signal correcting apparatus easily to perform decoding upon receipt of the stream.

It is another object of the present invention to prevent the occurrence of overflow / underflow of a video stream by enabling correction of a clock deviation caused by a transmission timing correction process.

[0009]

In order to solve the above-mentioned problems, the present invention is provided by a video stream transmitting apparatus.
Installed in the relay device that receives and retransmits the video stream
A video synchronization signal correction device,
Is added to the video stream sent from the
Time stamp and the system inside the video synchronization signal correction device.
From the value of the stem time clock, the video stream
Detects the deviation of the video synchronization signal between the sending device and the relay device
Means for detecting the video stream,
Delay by the time corresponding to the shift of the synchronization signal
Retransmitted in synchronization with the video synchronization signal of the relay device
And means for performing the following.

In this video synchronization signal correction device, the time stamp added to the video stream from the video stream transmission device and the value of the system time clock inside the video synchronization signal correction device determine the connection between the video stream transmission device and the relay device. detects deviation of the video synchronization signal during only the time corresponding to the deviation amount, the image in the this delay the retransmission from the synchronization signal correction device thus synchronously video stream sent to the video sync signal with the relay device The video stream from the device is retransmitted. This makes it possible to match the timing of the video synchronization signal of the relay device regardless of the timing of the video stream from the video stream transmission device. By applying the present invention to a relay device such as a video output device of a station, it is possible to easily perform stream switching at the time of stream retransmission in a digital broadcasting system and decode a stream at the time of reception.

This video synchronizing signal correction device can be constituted by, for example, a system time clock, a decoding unit, a delay buffer and the like. In this case, the timing of the video synchronization signal of the video synchronization signal correction device is determined by the time of the system time clock. The decoding unit determines a stream delay time necessary for correcting the video synchronization signal from the value of the system time clock and the value of the time stamp written in the stream. After the time stamp is rewritten to a value based on the system time clock in the video synchronization signal correction device, the data is transmitted after being delayed by the delay time in the delay buffer. Thus, the video stream can be synchronized with the video synchronization signal of the relay device.

Further, the decoding unit calculates a stream of system time clock and the video synchronization signal correcting device inside the system time clock deviation, deviation of GOP to the stream After greater than 1 frame synchronizing signal h outermost
Perform insertion / deletion of <br/> picture unidirectional prediction in a position of at least one picture after further system time clock sends rewrites a time stamp so that continuous. As a result, it is possible to correct the clock deviation caused by the transmission timing correction processing, and to prevent the overflow / underflow of the video stream from occurring.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of a digital broadcasting system using a video synchronization signal correction device according to an embodiment of the present invention. This digital broadcasting system uses the MPEG2 system, and
A digital video signal composed of a G2 transport stream is transmitted from a broadcasting station to a subscriber through a network. In this system, the video synchronization signal correction device converts a stream sent from an encoder in the broadcasting station. It is provided in a video output device that performs a relay process of receiving and retransmitting it to a subscriber via a network.

In the stream sending device 11, a camera 12
The video fetched from the MPEG-2 video stream is encoded by the encoder 13 in real time into an MPEG2 video stream.
It is multiplexed with the PEG2 transport stream and transmitted. The stream transmission device 11 uses the system time clock (STCe) 15 as a clock master, the time stamp of the transport stream is generated from the STCe, and the video synchronization signal from the video synchronization signal generation circuit 14 is also S.
Synchronous with TCe.

The video synchronization signal correction device 21 has a system time clock (STCs) 24, and the time stamp of the MPEG2 transport stream sent from the video synchronization signal correction device 21 to the network is generated from the STCs. The timing of the video synchronization signal of the video output device is defined based on STCs, and the time STCssync specified by the counter value of STCs is the timing of the video synchronization signal.

The video synchronizing signal correction device 21 includes a system time clock (STCs) 24, a decoding unit 22,
A delay buffer 23 is provided. The decoding unit 22 is necessary to correct the timing of the video synchronization signal of the stream from the value of the system time clock (STCs) 24 and the value of the time stamp written in the MPEG2 transport stream from the stream transmission device 11 Determine the appropriate stream delay time. Then, after the time stamp is rewritten to a value based on the system time clock (STCs) 24 in the video synchronization signal correction device 21, the data is transmitted after being delayed by the delay time in the delay buffer 23. Thereby, the MPEG2 transport stream from the stream transmission device 11 can be synchronized with the timing STCsync of the video synchronization signal of the video output device.

Further, the decoding unit 22 includes the STCe of the stream transmission device 11 and the STCe of the video synchronization signal correction device 21.
A clock deviation from Cs is calculated, and when the deviation becomes equal to or longer than one frame synchronization signal time, picture data is inserted / deleted into the stream in frame units and transmitted. In the stream, the time stamp is rewritten and transmitted so that the system time clock is continuous. This allows
The clock deviation caused by the transmission timing correction processing can also be corrected.

FIG. 2 shows the structure inside the decoding section 22 and its periphery. As shown in FIG. 2, the decoding unit 22 includes a PSI decoding unit 221, a PCR decoding unit 2
22, an intermediate buffer 223, and a ΔSTC0 table 224. The PSI decoding section 221
PSI (P included in the EG2 transport stream
program Specific Information
on, program specification information) and decode the PCR (P
packet ID of the packet including the program clock reference (program clock reference value)
(PCR PID) and the like. PCR
The decoding unit 222 determines the value of the PCR of the PCR packet and S
Using the TCs, clock-related processing for synchronizing signal correction is performed. Hereinafter, the specific processing contents of the PCR decoding unit 22 will be described with reference to FIG.

As shown in FIG. 2, the decoding unit 2
2 is a PSI decoding unit 221, a PCR decoding unit 22
2, intermediate buffer 223, and ΔSTC0 table 2
24. The PSI decoding unit 221 has an MPE
PSI (Pr) included in the G2 transport stream
ogram Specific Information
n, program specification information) and decode the PCR (Pr
packet ID of the packet including the program clock reference (program clock reference value)
(PCR PID) and the like. PCR
The decoding unit 222 determines the value of the PCR of the PCR packet and S
Using the TCs, clock-related processing for synchronizing signal correction is performed. Hereinafter, the specific processing contents of the PCR decoding unit 222 will be described with reference to FIG.

First, PSI decoding section 221
The PCR PID is checked from the SI and the PCR PI
D is provided to the PCR decoding unit 222 (step S11). In the PCR decoding unit 222 , each time a transport packet is received, its packet ID is
It is checked whether it is a PID or not, whereby a PCR is searched for in the transport packet (step S1).
2, S13). Upon receiving the first PCR, the PCR decoding unit 222 calculates the initial deviation time ΔSTC0 by subtracting the value of the PCR from the value of the STCs at that time, and stores the ΔSTC0 in the ΔSTC0 table 224 (steps S14 and S15). ).

The transport packets written in the intermediate buffer 223 are sequentially read by the stream analysis unit 225, and the processing shown in FIG. 4 is performed to determine the delay time Td.
The transport packet whose time stamp is rewritten according to the STCs is written to the delay buffer 23.

That is, as shown in FIG. 4, when the stream analysis unit 225 reads the transport packet from the delay buffer 23, first, the stream analysis unit 225 checks whether the ΔSTC0 exists in the ΔSTC0 table 224 to check whether the ΔSTC0 exists. It is determined whether or not has been calculated (step S22). If ΔSTC0 has not been calculated, the process for synchronization cannot be started, and the transport packets up to that time are discarded (step S26). If ΔSTC0 has been calculated, it is determined whether or not the delay time has been calculated (step S23). If not, processing for calculating the delay time is started (steps S24, S25).

In this case, in step S24, first, a decoding time stamp DTS (Decoding Time Stamp) is added to the read transport packet.
It is checked whether or not p) exists, and if not, the reproduction output time stamp PTS (Presentatio)
It is checked whether or not (n Time Stamp) exists. The DTS is provided for the case where the decoding timing and the display timing are different between the I picture and the P picture in the MPEG video stream, and the DTS is used for the decoding in the B picture and the low delay mode. Since the timing and display timing are simultaneous, P
This is because only the PTS is added because the values of the TS and the DTS match.

If there is only DTS or PTS,
Based on this, the delay time is calculated in step S25. The processing for calculating the delay time is performed according to the procedure shown in FIG. That is, first, a converted value DTS ′ (DTS ′ = DTS + ΔSTC0) of the DTS (DTS ′ = DTS + ΔSTC0) is obtained for the DTS (the same applies to the PTS) in consideration of the value of ΔSTC0 (step S41). After this, DTS 'is changed to STCs
A process of synchronizing with the above synchronizing signal, that is, STCsync is performed (step S42). Here, DTSs after the synchronizing process is obtained by the value of STCsync closest to DTS 'in time + 1 frame time. . Here, the reason why the time is increased by one frame time is to prevent a problem that an underflow occurs immediately after the synchronization process due to a clock deviation between STCe and STCs.

Next, the delay time Td (= DTSs-DTS ') is obtained by subtracting DTS' from DTSs (step S43). As described above, Td is a value determined by the deviation of the video synchronization signal between the video synchronization signal correction device 21 and the video stream transmission device 11, and Td is the value of the clock deviation of the video synchronization signal between the video synchronization signal correction device 21 and the video stream transmission device 11. Since the correction is also performed on a video synchronization signal basis, the delay time is constant for the video stream transmission device 11.

When the delay time is obtained in this way,
Next, the process proceeds to step S27 in FIG. 4, and a change in the value of ΔSTC0 on the ΔSTC0 table 224 is checked. ΔS
If the value of TC0 is increased, a picture is added to deal with the underflow (step S2).
8) If the value of ΔSTC0 is reduced, a picture is deleted to cope with the overflow (step S29). Thereafter, the time stamp (PCR, DTS, PTS) of the corresponding transport packet is rewritten based on the delay time Td, and then the transport packet is written into the delay buffer 23 (steps S30, S31). In the delay buffer 23, the bucket is transmitted after being delayed by the delay time Td.

The conversion of the time stamp is performed by the following equation. PCRs = PCR + ΔSTC0 + Td DTSs = DTS + ΔSTC0 + Td PTSs = PTS + ΔSTC0 + Td Next, the process of inserting and deleting a picture from a stream performed by the stream analysis unit 225 will be described.

When the delay time is obtained in this way,
Next, the process proceeds to step S27 in FIG. 4, and a change in the value of ΔSTC0 on the ΔSTC0 table 224 is checked. ΔS
When the value of TC0 is increased, a picture is inserted to cope with the underflow (step S2).
8) If the value of ΔSTC0 is reduced, a picture is deleted to cope with the overflow (step S29). Thereafter, the time stamp (PCR, DTS, PTS) of the corresponding transport packet is rewritten based on the delay time Td, and then the transport packet is written into the delay buffer 23 (steps S30, S31). In the delay buffer 23, the bucket is transmitted after being delayed by the delay time Td.

When inserting a picture, the picture is inserted under the following conditions. Insert a universal P-picture on the stream after the last picture of the GOP.

The conditions of the universal P-picture to be inserted are as follows: temporal reference = temporal referrer of last displayed Picture
ence + 1 where temporal reference is GOP
Indicates the number of the picture in the.

Vbv delay = vbv delay of the picture next to the inserted universal P picture. Code amount to be inserted = code amount of inserted universal P picture + stuffing = bit rate × 1 frame time.

In the case of deleting a picture, processing is different depending on whether M = 1 or M = 2 or more. If M = 1, the last two P pictures of the GOP are deleted and one universal P picture is inserted.

The conditions of the universal P-picture to be inserted are as follows: temporal reference = tempo of the picture displayed first among the deleted P-pictures
ral reference · vbv delay = vbv delay of a picture displayed earlier among deleted P pictures · total code amount to be inserted = code amount of P picture to be inserted +
Stuffing 0 = total code amount of deleted pictures−
Bit rate x 1 frame time If M = 2 or more, delete the P picture displayed at the end of the GOP and all B pictures displayed before it, and insert a universal P picture one less than the number of deleted pictures I do.

The conditions of the universal P-picture to be inserted are as follows: temporal reference = tempo of the picture displayed first among the deleted B-pictures
ral reference · vbv delay = vbv delay of the picture displayed earlier among the deleted B pictures · total code amount to be inserted = total code amount of Ppicture to be inserted + stuffing 0 = total code amount to be deleted-bit rate x 1 Frame Time When the above processing is performed, the data remaining in the delay buffer 23 is reduced by (bit rate × 1 frame time) from the start of the operation just before the picture is inserted. At this time, one frame time is added to the delay time when calculating the delay time Td so that the delay buffer 23 does not underflow. In order to perform these processes, the size of the delay buffer 23 needs to be at least (bit rate × 3 frame times).

Hereinafter, the processing for inserting and deleting a picture will be specifically described with reference to FIGS. FIG.
Is an example of inserting a P picture. Here, GOP
After the last picture (B13), the same universal P picture as the P picture immediately before, that is, the 14th P picture (P14) is replaced with the 15th P picture (P1).
5).

FIG. 7 shows a case where a picture is deleted (M =
In this example, the last two pictures (P13, P14) of the GOP are deleted, and the P picture that is the same as the previous P picture, that is, the twelfth P picture (P12) is the thirteenth picture. P picture (P13)
Has been inserted as.

FIG. 8 shows a case where a picture is deleted (M =
In this example, the P picture (P14) displayed at the end of the GOP and the B pictures (B12, B13) displayed before it are all deleted, and these three deleted pictures are deleted. Two universal Ps one less than
Pictures P12 and P13 are inserted.

Next, an example of a video output device in which streams transmitted from a plurality of stream transmission devices 11 are received by the video synchronization signal correction device 21 and one of them is selected and transmitted at any time will be described.

FIG. 9 shows an example of the video synchronizing signal correcting device 21 provided in the video output device for selecting one from the streams sent from the three video stream transmitting devices 11a, 11b, 11c.

The video stream transmitting devices 11a, 11b,
11c has an independent system clock STCe, and the video synchronization signal is synchronized with the system time clock of each video stream transmission device. Each of these video stream transmission devices 11a, 11b, 11c
The stream is transmitted to the same network in the form of an MPEG2 transport stream.

The video signal output device is provided with video synchronization signal correction units 21a, 21b, 21c corresponding to the stream transmission devices 11a, 11b, 11c, respectively.
There is one system time clock (STCs) 24 in the video output device, and each video synchronization signal correction unit uses the same system time clock STCs.

The stream coming from the network is sent to each stream transmitter 11 by the stream distributor 31.
a, 11b, and 11c, which are divided into streams sent from the video synchronization signal correction units 21a, 21b, and 2 respectively.
Enter 1c. Here, the frame synchronization with respect to the system time clock is corrected, and the stream is converted into a stream synchronized with the system clock STCs of the video output device. The synchronization processing and the picture insertion and deletion processing corresponding to the clock deviation in each video synchronization signal correction unit 21a, 21b, 21c are performed in the same manner as the video synchronization signal correction 21 in FIG.

The stream selection unit 32 selects one of the streams output from the video synchronization signal correction units 21a, 21b, 21c and sends it to the network, while discarding the other streams.

When the video output apparatus switches streams, the following procedure is performed. Each video synchronization signal correction unit 21
a, 21b, and 21c internally hold the values of the DTS and PTS of the first picture of the latest GOP to be sent from now on, and can read them from the stream selection unit 32. Also, the access point of the stream is the random access of the transport stream.
It is assumed that it can be understood by the ss indicator.

The stream transmitted before the switching is stopped until the end of the GOP is used. The number of pictures to be inserted between the PTS of the last picture of the previously transmitted stream and the PTS of the first picture to be transmitted next is determined. The number of universal P-pictures is inserted into the stream, and then stuffing is transmitted until the head of the newly transmitted stream is transmitted. This is shown in FIG.

In FIG. 10, the same universal P pictures P15, P16, P17, P18 as P14 are inserted after the last picture B13 of the GOP of stream 1, and thereafter, the GOP of stream 2 is switched.

[0047]

As described above, according to the present invention,
The transmission timing can be corrected so that each video bit stream with a different video synchronization signal timing is created using the same video synchronization signal, making it easy to switch streams during retransmission and decode the stream at reception. It is possible to do. Further, since a clock deviation caused by the transmission timing correction processing can be corrected, it is possible to prevent an overflow / underflow of the video stream from occurring.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a video synchronization signal correction device according to an embodiment of the present invention.

FIG. 2 is an exemplary block diagram showing a configuration of a decoding unit provided in the video synchronization signal correction device of the embodiment.

FIG. 3 is an exemplary flowchart illustrating a procedure performed by a PCR decoding unit provided in the video synchronization signal correction device of the embodiment.

FIG. 4 is an exemplary flowchart illustrating a procedure performed by a stream analysis unit provided in the video synchronization signal correction device of the embodiment.

FIG. 5 is an exemplary flowchart showing the procedure of a calculation process of a delay time Td in the video synchronization signal correction device of the embodiment.

FIG. 6 is an exemplary view for explaining a picture insertion operation in the video synchronization signal correction device of the embodiment.

FIG. 7 is an exemplary view for explaining a picture deletion operation (M = 1) in the video synchronization signal correction device of the embodiment.

FIG. 8 is an exemplary view for explaining a picture deletion operation (M = 3) in the video synchronization signal correction device of the embodiment.

FIG. 9 is an exemplary block diagram illustrating a configuration of a video output device configured by using a plurality of video synchronization signal correction devices according to the embodiment;

FIG. 10 is a diagram for explaining a stream switching operation in the video output device of FIG. 9;

[Explanation of symbols]

11, 11a, 11b, 11c...
12 camera, 13 decoder, 14 video synchronization signal generation circuit, 15 system time clock (STCe),
21, 21a, 21b, 21c video synchronization signal correction device, 22 decoding unit, 23 delay buffer, 24 system time clock (STCs), 221 PSI decoding unit, 222 PSR decoding unit, 223 intermediate buffer, 224... ΔSTC0 table, 225.

Claims (4)

(57) [Claims] 1. A video synchronization signal correction device provided in a relay device for receiving and retransmitting a video stream sent from a video stream transmission device, the video synchronization signal correction device being added to a video stream sent from the video stream transmission device. Means for detecting a deviation of a video synchronization signal between the video stream transmission device and the relay device from the time stamp and the value of the system time clock inside the video synchronization signal correction device; and Means for delaying by a time corresponding to the shift of the video synchronization signal, and retransmitting the video synchronization signal in synchronization with the video synchronization signal of the relay device. 2. A system time clock inside the video stream transmission device, based on a time stamp added to a video stream sent from the video stream transmission device and a value of a system time clock inside the video synchronization signal correction device. Means for detecting a clock deviation from a system time clock in the video synchronization signal correction device, and a video stream sent from the video stream transmission device based on the detected magnitude of the clock deviation. Means for correcting the clock deviation by inserting or deleting a unidirectionally predicted picture at the position of at least one picture at the end of the GOP and rewriting the time stamp. 2. The video synchronization signal correction device according to 1. 3. A video synchronization signal correction device provided in a relay device that receives a plurality of video streams respectively transmitted from a plurality of video stream transmission devices, selects one video stream from the video streams, and retransmits the selected video stream. A time stamp added to each of the plurality of video streams sent from the plurality of video stream transmission devices and a value of a system time clock inside the video synchronization signal correction device, the plurality of video stream transmission devices, Means for detecting a shift of the video synchronization signal between the relay devices, and a video synchronization signal of the relay device by delaying each of the plurality of video streams by a time corresponding to the shift of the detected video synchronization signal. Means for synchronizing, and a plurality of video streams synchronized with a video synchronization signal of the relay device Video synchronization signal correction apparatus characterized by comprising a means for re-transmitting the selected one of the video streams from the. 4. A method according to claim 1, wherein the plurality of video streams are sent from the plurality of video stream transmitting devices and the system time clock value in the video synchronization signal correcting device. Means for detecting a clock deviation between a system time clock inside the stream transmission device and a system time clock inside the video synchronization signal correction device; and the plurality of video streams based on the magnitude of the detected clock deviation. The clock deviation is corrected by inserting or deleting a unidirectionally predicted picture at the position of at least one picture at the end of a GOP and rewriting the time stamp for a plurality of video streams sent from the sending device. And means for performing 3. The video synchronization signal correction device according to 3.