JPH11177921A - Digital data edit method and digital data edit device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reproduce an image without disturbance at a switching point of a data stream even by a decoder that is unable to correctly receive a broken link flag. SOLUTION: A data stream from a main station is given to a demultiplexer 11, where the stream is separated into video and audio streams, and the video stream is fed to a multiplexer 16 via a switch 14a and a buffer 15. A server 12 stores data streams replaced by branch stations and skip pictures that are pictures to replace discontinuous B pictures consisting of macro blocks subject to unidirectional prediction only. A system controller 13 is provided with a detection section 13a that detects discontinuous B pictures at connection points between a video stream from the main station and video streams replaced at branch stations and with a stuffing amount calculation section 13b. The replaced and combined data streams are multiplexed again by the multiplexer 16 and outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a digital data editing method and a digital data editing apparatus used for editing a digital data stream composed of a plurality of data coded and multiplexed by compression.

[0002]

2. Description of the Related Art In a conventional television broadcast for transmitting an analog signal using a terrestrial wave or a cable, a broadcast program (program) is transmitted from a main station to a viewer via a local branch office. At this time, the head office distributes a program for the whole country, and the branch office transmits a part of the program by replacing it with a program for each region.

FIG. 5 shows a splicing process when a required program is replaced.
As a typical example of the above, a process in which an advertisement (so-called commercial) portion of a program for the whole country distributed from the head office is replaced with a commercial for each region at each branch office in each region is shown.

[0004] That is, a branch station is a portion of a broadcast program sent from the main station other than a commercial (main broadcast).
A is transmitted as it is, and only the commercial part B is a local commercial C prepared in advance for the reception area of the own station.
And send it. Then, after the end of the transmission of the local commercial C, the main broadcast program A 'transmitted from the main station is transmitted again. Such a replacement process of a commercial program is called a commercial insertion.

[0005] When the above-mentioned commercial insertion is introduced into digital broadcasting, it is necessary to perform a process of combining the data stream sent from the main station and the data stream sent from the branch station.

FIG. 6 shows a transformer in which a plurality of programs are multiplexed on the transmitting side and sent out via a transmission medium, and the receiving side can selectively receive any of the plurality of programs. 1 shows a configuration example of a multiplexing system using a port stream.

In this example, the transmitting side is a base station (uplink station) for digital satellite broadcasting, the transmission medium is a satellite broadcasting line, and the receiving side is a so-called set-top box for receiving satellite broadcasting.

On the base station side, each program (channel)
Are multiplexed by the video encoder and the audio encoder of the multiplexers 61a to 61n. Here, each program is, for example, MPEG (ISO / IEC IS1).
1172 and IS13818).

[0009] The bit stream of each program in which the video bit stream and the audio bit stream are put together is further multiplexed by the transport multiplexer 62a of the multiplexing device 62 and put into one transport stream. After that, the signal is modulated by the modulator 62b and sent to the transmission medium 63.

[0010] The transport stream transmitted to the receiving side via the transmission medium 63 is demodulated by the demodulator 64a of the set-top box 64, demultiplexed by the demultiplexer 64b, and returned to a plurality of programs. From among them, the program of the channel selected by the viewer with the remote controller 66 or the like is selectively taken out and sent to the video decoder 64c and the audio decoder 64d.

The video signal and the audio signal decoded by the video decoder 64c and the audio decoder 64d are output to the monitor 65.

As described above, in an actual broadcast such as a digital satellite broadcast, a process of editing and combining a video data stream and an audio data stream as described above is required.

FIG. 7 shows a configuration example of a system for realizing the combination of the transport stream sent from the head office and the elementary streams stored in the server (commercial bank stream server). Here, a case is shown where the video stream and the audio stream of one program are combined at the level of the original signal.

[0014] In the commercial broadcast program, the video elementary stream and the audio elementary stream are stored in the memories 72 a and 7 of the server 72.
2b are stored in advance, and are replaced with commercial parts sent from the head office and sent.

The transport stream sent from the head office is first decomposed by the demultiplexer 71 into a video elementary stream and an audio elementary stream, and then the video stream and the audio stream are respectively switched by the switches 74a and 74b to the server 72. Are switched to a local video stream and an audio stream from the, and are multiplexed again by the multiplexer 76 and sent out.

Next, one of image and sound signal compression methods applied to the digital data editing apparatus and the digital data editing method according to the present invention, which is an MPEG (Moving Picture Experts Group) that performs image compression by predictive coding.
p) The method will be described.

For encoding an image according to the MPEG system, 3
Different coding modes are used. One of them is a mode in which prediction is not performed, and the obtained image is called an intra-coded image (I-picture). The second is a mode to which forward prediction is applied, and the obtained image is called a forward prediction code image (P picture). The third is a mode in which forward prediction and backward prediction are applied, and the obtained image is called a bidirectional predicted image (B picture).

FIG. 8 shows how an image is predictively coded by the MPEG method.

As shown in FIG. 8A, a group consisting of a series of images starting from a B picture and ending with a P picture is called a GOP (Group Of Pictures). In a normal prediction structure, the N-th G
The B picture of GOP (N) which is OP is GOP (N)
And the I-picture at the back of it and (N-
The prediction encoding is performed with reference to the image of GOP (N-1) which is the 1) th GOP.

However, in order to perform bidirectional prediction, a future predicted image must be coded first. For this reason, at the time of encoding, as shown in FIG. 8B, the encoding order is such that the order of the images is switched to generate a bit stream, and the order of the images is changed so that each GOP starts from an I picture ( Reordering). The encoded bit stream is also in this order when transmitted.

If a bit stream to be predictively coded by the method shown in FIG. 8 is simply switched, the reference picture of the predicted picture is replaced with a different picture by combining the bit streams.
A case occurs where the first B picture of the GOP is not correctly reproduced.

FIG. 9 shows an example in which a discontinuous B picture cannot be correctly reproduced at the connection portion due to the combination of bit streams as described above.

In this example, GOP (N), which is the Nth GOP of the bit stream sent from the head office, is replaced by GOP (N) 'on the branch office side. At this time, since the reference image to be referred to by the first two B pictures 91 of the bit stream GOP (N) ′ to be replaced by the branch station does not exist in the GOP (N−1) in front of this, this BOP Picture 91 is not correctly reproduced. Similarly, when returning from the bit stream replaced by the branch station to the bit stream of the main station, the reference images to be referred to by the first two B pictures 92 of GOP (N + 1) are included in GOP (N) ′. This 2 because it does not exist
The two B pictures 92 are not correctly reproduced.

Here, a case is shown where the number of B pictures at the head of each GOP is two, but the number of B pictures is not limited to two.

The above problem can be solved by using a closed GOP which can be completely encoded within a GOP if the bit stream to be replaced at the branch station can be encoded in advance. it can. Note that a closed GOP flag is set during encoding to indicate that the first few B pictures of the GOP do not depend on the previous GOP.

FIG. 10 illustrates a case in which bit streams are combined by coding in advance using a closed GOP.

That is, a case is shown in which the head of the bit stream of the replacement part at the branch station and the part returning from the replacement part to the bit stream of the main station is coded using a B picture which is a closed GOP and restricted to only backward prediction. I have.

The closed GOP flag is prepared as an MPEG standard so that it can be used in such a case.

However, the method using the closed GOP flag can be applied when the bit stream to be replaced can be encoded in advance, but cannot be applied when it is not expected that the bit streams will be connected. . As described above, when coding cannot be performed in advance using a closed GOP, a broken link (brok link) is used.
en_link) flag, and the decoder can be reproduced by performing a process of freezing the discontinuous B picture at the head of the GOP on the decoder side.

That is, the broken link flag is
A flag that is set when a bit stream that is not a closed GOP is cut and connected by editing,
When the broken link flag is present, the decoder
Some discontinuous B pictures at the beginning of the OP cannot be displayed.

FIG. 11 shows an example in which when a data stream cannot be encoded in a closed GOP in advance, the screen is frozen using a broken link flag to prevent a distorted screen from being displayed.

That is, when the broken link flag is 1 at the head of the GOP, the discontinuous B picture 111 and the discontinuous B picture 112 at the head of the GOP are determined to be disturbed and displayed. Instead, the previous image is displayed frozen.

The broken link is a flag prepared in advance in the MPEG standard so that it can be used in such a case.

[0034]

However, among the decoders supplied to the market and actually used, there are decoders which cannot correctly interpret the above-mentioned broken link or the like and perform the freeze processing of the screen. In such a decoder, there is a problem that an image cannot be correctly reproduced only by setting a broken link flag for a discontinuous B picture in which an image is disturbed and transmitting data in anticipation of processing by the broken link.

The present invention has been made to solve such a problem, and has been developed in accordance with ISO / IEC IS1117.
The same effect can be obtained without using the broken link flag shown in 2-2 and IS13818-2, and a digital data editing method and a digital data editing method capable of reproducing a screen without disturbance even in a decoder that cannot correctly receive a broken link. It is an object to provide a digital data editing device.

[0036]

A digital data editing method according to the present invention, proposed to solve the above-mentioned problems, comprises a first digital data stream and a second digital data stream, each of which is constructed using predictive coding. In a digital data editing method for switching between data streams,
At the beginning of the second digital data stream switched from the first digital data stream,
A detection step of detecting that there is a discontinuous bidirectional predicted image that is not correctly reproduced due to the lack of a reference image, and when a discontinuous bidirectional predicted image is detected in the detection step,
And replacing the image with an image formed using only one-directional prediction.

Further, a digital data editing apparatus according to the present invention proposed to solve the above-mentioned problem includes a first digital data stream and a second digital data stream, each of which is constructed using predictive coding. In the switching digital data editing apparatus, detection is performed to detect that a discontinuous bidirectional predicted image that is not correctly reproduced due to a lack of a reference image is provided at the head of the second digital data stream that is switched from the first digital data stream. And a replacement means for, when the detecting means detects a discontinuous bidirectional image, replacing the discontinuous bidirectional image with an image formed using only one-way prediction.

According to the present invention described above, even a decoder that cannot correctly receive a broken link can reproduce a screen without disturbance at a switching portion of a digital data stream.

[0039]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. Hereinafter, the digital data editing apparatus of the present invention will be described first, and then the digital data editing method of the present invention will be described with reference to the configuration.

FIG. 1 shows an example of the configuration of a digital data editing apparatus according to the present invention.

This digital data editing apparatus is capable of editing by switching between a first digital data stream and a second digital data stream. Specifically, the digital data editing apparatus advertises a broadcast program distributed from the head office. It is used to replace an advertising program (so-called commercial) portion with a local commercial broadcast program at a branch office, or to switch news, weather forecasts, etc., to a nationwide broadcast and to each region.

In the following, all digital data streams are MPEG (Moving Picture Experts Groove).
up) The description will be made on the assumption that compression encoding is performed by the method.

The data stream sent from the head office is decomposed by the demultiplexer (DEMUX) 11 into a video stream and an audio stream. The video stream is sent to the system controller 13 and to the multiplexer 16 via the switch 14a and the buffer 15. The audio stream is sent to the multiplexer 16 via the switch 14b.

The server 12 is a so-called commercial bank, in which video elementary streams and audio elementary streams of a commercial program to be replaced by a branch office are stored in memories 12a and 12c each constituted by a hard disk device or the like. The memory 12b of the server 12 also stores a skip picture, which is an image composed of skip macro blocks of only backward prediction, for replacing a discontinuous B picture at the head of a GOP.

The skip picture can be generated irrespective of the I picture, and has a predetermined value whose residual from the I picture is 0. Therefore, the data amount is sufficiently small. For this reason, the memory 12b can be configured using a semiconductor memory element.

The system controller 13 is a means for controlling the operation of the digital data editing apparatus. The system controller 13 monitors a video stream sent from the head office and a video stream to be replaced by a branch office, and removes a discontinuous B picture at a connection point. Detecting unit 13a for detecting and buffer 1
5 is provided with a stuffing amount calculation unit 13b that calculates an amount of stuffing that does not cause a failure.

The video stream and audio stream combined through such processing are multiplexed again by the multiplexer 16 and output.

Next, a digital data editing method according to the present invention will be described with reference to the configuration and operation of the above-described digital data editing apparatus according to the present invention.

The digital data editing method according to the present invention does not use a closed GOP (closed_GOP) or a broken link (broken_link), and can obtain the same effect as in the case of using these. At the beginning of the second digital data stream switched from the first digital data stream, it is detected that there is a discontinuous bidirectional predicted image (B picture) which is not correctly reproduced because there is no reference image. When a picture is detected, a process of replacing the picture with an image configured using only one-way prediction is performed.

At the connection point between the video stream from the main station and the video stream (video elementary stream) prepared at the branch station, the reference image of the first B picture of the video elementary stream is lost due to the editing operation. The image is disturbed by the connection (combination) of the two bit streams.

Therefore, in the digital data editing method according to the present invention, the connection point is detected by detecting a cue signal included in the transport stream sent from the head office, and the cause of image distortion is detected. A discontinuous B picture at the above connection point is detected. This processing is performed by the detection unit 13a in the digital data editing apparatus of FIG.

At this time, an amount of stuffing that does not cause a failure such as overflow or underflow in the buffer 15 is calculated. Here, the stuffing refers to inserting dummy data (generally, 0 is used) for adjustment such as keeping the data length constant.
The calculation of the stuffing amount is performed by the stuffing amount calculation unit 13b in the digital data editing apparatus of FIG. Specifically, when replacing a discontinuous bidirectionally predicted image (B picture) with an image configured using only the above-described unidirectional prediction, GOP (N) ′ that has already been encoded.
In this case, dummy data corresponding to the insufficient data amount is packed so as to match the data amount of the buffer, and the buffer occupancy amount is matched.

The video stream from the main station, the video elementary stream connected to the video stream from the main station, the one-way prediction, according to the control signal indicating the detection result of the discontinuous B picture at the connection point of the bit stream. Either a backward predicted image or stuffing data (= 0) is selected, and these are switched and connected.

In the digital data editing apparatus shown in FIG. 1, the video elementary stream is stored in the memory 1 of the server 12.
From 2a, backward prediction images are sent from the memory 12b of the server 12, and these are selected by the switch 14a. The switch 14b similarly selects one of the audio stream sent from the head office and the audio elementary stream sent from the memory 12c of the server 12.

FIG. 2 shows how a first digital data stream and a second digital data stream are connected as an embodiment of the digital data editing method according to the present invention.

Here, GOP (N) which is a part of the first digital data stream sent from the head office to the branch office
Is changed to GOP (N) ′, which is a second digital data stream prepared in advance at the branch office. Specifically, a publicity program (a so-called advertising program) of a broadcast program distributed from the main office is used. In this example, a (commercial) portion is replaced with a local commercial broadcast program at a branch office. For convenience of explanation, the second stream is shown to be composed of only one GOP (N) ′, but the number of GOPs is arbitrary.

As described above, if the local commercial broadcast program replaced at the branch office is simply connected to the digital data stream sent from the main office, the B picture 21a at the head of the local commercial part has no reference image that should be in front of it. Therefore, in the digital data editing method according to the present invention, these discontinuous B
The picture is replaced with a skip picture 21b, which is composed entirely of skip macroblocks with only unidirectional prediction. Normally, backward prediction is used for this one-way prediction, but since skip pictures can be generated independently of I-pictures, they may be generated using forward prediction. Thereby, the discontinuous B picture 21a at the head of GOP (N) 'is
Will be frozen, and the same effect as the conventional processing performed using the broken link can be obtained.

Further, by performing the same processing as that performed on the discontinuous B pictures in the replacement part when returning to the bit stream of the main office, it is possible to replace the middle of the program sent from the main office. It becomes possible. That is, even when returning from the bit stream replaced by the branch station to the bit stream of the main station, G
The discontinuous B picture 22a at the head of OP (N + 1) is
A similar effect can be obtained by replacing the skipped picture with a skip picture 22b composed of skip macroblocks that are all unidirectionally predicted only.

In the present invention, the size of the image data is adjusted by using stuffing so as to prevent inconsistency in the buffer capacity during the processing using the one-way prediction screen.

Next, the matching of the buffer occupancy will be described.

FIG. 3A shows an example of a locus of the buffer occupancy of the video stream A transmitted from the head office.

The commercial part CM of the video stream A from the head office is replaced by another commercial (local commercial) CM 'at the branch office. The local commercial CM 'replaced by the branch office is adjusted in advance to the same length as the commercial CM sent from the main office.

On the other hand, FIG. 3B shows an example of the trajectory of the buffer occupancy on the branch station side. Here, the two B pictures at the head of the commercial replacement portion CM 'are configured to prevent the buffer from overflowing or underflowing by using a B picture which is a skip picture only for backward prediction and a stuffing bit as shown in the figure. Has been adjusted. Specifically, in order to make the data amount (buffer occupancy amount) of the stuffed portions 31, 32, 33, and 34 of the B picture coincide with the data amount of the image before performing the replacement process, the data amount 35, 3
The stuffing corresponding to 6, 37, 38 is performed.

As a result, the broken link (brok
Even for a decoder that cannot process (en_link), it becomes possible to perform the connection processing of the video data stream at the bit stream level.

FIG. 4 shows a basic procedure of the digital data editing method according to the present invention described above.

In step S1, first, the process waits for detection of a cue signal inserted from the data stream to indicate switching. When a cue signal is detected, the process proceeds to step S2.

In step S2, the process waits for the detection of a discontinuous B picture in which the leading image of the GOP is disturbed. Here, when a discontinuous B picture whose image is disturbed is detected, the following process (1) or (2) is performed.

(1) When the value of the broken link flag is 1, the value is set to 0 and the leading discontinuous B
The above-described processing is performed on the picture.

(2) When the value of the broken link flag is 0 and the GOP is not a closed GOP,
The above-described processing is performed on the discontinuous B picture at the head of the GOP.

In step S3, the necessary stuffing amount "staffing" is calculated. Where the original discontinuous B
When the value of the picture is “B_old” and the value of the skip image B_skip is “skip_B”, the calculation is performed as skip_B = B_skip staffing = B_old−B_skip.

Then, in step S4, step S3
And the stuffing amount st
Affing is inserted into the stream.

In the above description, the case where the digital data stream of the broadcast program is switched between the head office of the broadcasting station and the branch office is described as an example, but the application of the present invention is not limited to this. For example, a moving image signal and an audio signal are recorded on a recording medium such as a magneto-optical disk or a magnetic tape, and are reproduced and displayed on a display or the like, a video conference system, a video phone system, a broadcasting device, or the like. Transmitting a moving image signal and an acoustic signal from a transmission side to a reception side via a transmission path,
This can be widely applied, for example, when this is displayed on the receiving side.

[0073]

According to the digital data editing method and the digital data editing apparatus of the present invention, when switching the data stream, the discontinuous B picture at the head of the part to be combined is replaced with a screen constituted by unidirectional prediction. Since the processing is performed, even when the reference image is replaced with a different image, it is possible to prevent the reproduced image from being disturbed even if the data streams are combined at an arbitrary position.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of a digital data editing device according to the present invention.

FIG. 2 is a diagram for explaining connection of two digital data streams as one embodiment of a digital data editing method according to the present invention.

FIG. 3 is a diagram for explaining consistency of buffer occupancy in the present invention.

FIG. 4 is a flowchart showing a basic procedure of a digital data editing method according to the present invention.

FIG. 5 is a diagram for describing splicing of data streams.

FIG. 6 is a diagram illustrating a configuration example of a multiplexing system using a transport stream.

FIG. 7 is a diagram illustrating a specific configuration example of a multiplexing system using a transport stream.

FIG. 8 is a diagram for explaining how an image is predictively encoded by the MPEG method.

FIG. 9 is a diagram for describing an example in which an image cannot be correctly reproduced due to the combination of bit streams.

FIG. 10 is a diagram for describing a case where bit streams are combined by encoding in advance with a closed GOP.

FIG. 11 is a diagram illustrating a process of freezing a screen using a broken link so as not to display a disordered screen.

[Explanation of symbols]

Reference Signs List 11 multiplexer, 12 server, 13 system controller, 13a detection unit, 13b stuffing amount calculation unit, 14a, 14b switch, 1
5 buffers, 16 multiplexers

Claims (12)

[Claims] 1. A digital data editing method for switching between a first digital data stream and a second digital data stream, each of which is configured using predictive coding, wherein the first digital data stream is switched from the first digital data stream. 2 at the beginning of the digital data stream,
A detection step of detecting that there is a discontinuous bidirectional predicted image that is not correctly reproduced due to the lack of the reference image; and And replacing the image with an image constituted by using the digital data editing method. 2. The digital data editing method according to claim 1, wherein the image constituted by using only one-way prediction is constituted by a skip macroblock using only backward prediction. 3. The digital data editing method according to claim 1, wherein the image formed by using only one-way prediction is constituted by a skip macroblock using only forward prediction. 4. The digital data editing method according to claim 1, wherein the image formed using only one-way prediction is adjusted to an image having a predetermined data amount by stuffing. 5. A method according to claim 1, wherein the first digital data stream and the second digital data stream are each formed by multiplexing a plurality of image signals and / or audio signals which are compression-encoded by the MPEG system. 2. The digital data editing method according to claim 1, wherein: 6. The first digital data stream is a broadcast program transmitted from the head office to a branch office,
2. The digital data editing method according to claim 1, wherein said second digital data stream is a broadcast program to be replaced by a part of said broadcast program at said branch station. 7. A digital data editing device for switching between a first digital data stream and a second digital data stream, each of which is configured using predictive coding, wherein the first digital data stream is switched from the first digital data stream. 2 at the beginning of the digital data stream,
Detecting means for detecting that there is a discontinuous bidirectional predicted image that is not correctly reproduced due to lack of a reference image, and when the detecting means detects a discontinuous bidirectional image,
A digital data editing device comprising: a replacement unit that replaces the image with an image configured using only one-way prediction. 8. The digital data editing apparatus according to claim 7, wherein the image constituted by using only one-way prediction is constituted by a skip macroblock using only backward prediction. 9. The digital data editing apparatus according to claim 7, wherein the image formed by using only one-way prediction is constituted by a skip macroblock using only forward prediction. 10. A stuffing amount calculating means for calculating a stuffing amount of an image formed using only one-way prediction, wherein the image is adjusted to an image of a predetermined size by stuffing. The digital data editing device according to claim 7. 11. The first digital data stream and the second digital data stream are each formed by multiplexing a plurality of image signals and / or audio signals that have been compression-encoded by the MPEG system. The digital data editing device according to claim 7. 12. The first digital data stream is a broadcast program transmitted from a head office to a branch office, and the second digital data stream is a broadcast program to be replaced by a part of the broadcast program at the branch office. 8. The digital data editing apparatus according to claim 7, wherein the digital data editing apparatus is a program.