JPH11262000A - Video signal transmission method and apparatus - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a video signal transmission device capable of shortening a delay time in a vbv_buffer occupying most of the entire delay time and adaptable to a bidirectional communication system which has been difficult to adapt conventionally. . A transmission side writes compressed data compressed at a predetermined bit rate to a transmission side buffer memory at the compression rate, and intermittently reads out the data at a transmission rate of a transmission path higher than the compression rate by a predetermined speed. For compressed data,
Reference time information and predetermined time stamp information calculated from the relationship between the compression rate and the transmission rate are added and transmitted to the transmission path, and on the receiving side, the compressed data fetched from the transmission path is transmitted to the transmission path. Intermittently writing to the receiving buffer memory at a rate, based on the extracted reference time information and the predetermined time stamp information, read the compressed data from the receiving buffer memory at a speed corresponding to the compression bit rate, A video signal transmission system that performs a decoding process on the compressed data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal transmission processing technique, and more particularly, to MPEG1, MPEG2 (IS
O / IEC 11172-2, ISO / IEC 138
The present invention relates to a method for transmitting a video signal (also referred to as a video stream) compressed according to 18-2).

[0002]

2. Description of the Related Art In recent years, ATM (Asynchronous Transfer M)
ode), a digital FPU (Field Pick-up Unit), and a device for transmitting a video signal through a digital transmission path such as digital satellite broadcasting are rapidly increasing. And many of them
Compression techniques such as MPEG1 and MPEG2 are used. FIG. 2 shows an example of a conventional technique in which a video signal is compressed at a fixed rate by MPEG1 or MPEG2 and transmitted, and the operation will be briefly described. First, as initial processing, the CPU 45 sets an average compression bit rate or a compression rate (hereinafter, simply referred to as a compression bit rate or a compression rate) of the video signal in consideration of the transmission rate of the transmission path 39 in the compression encoder unit 29. . Compression encoder unit 29
Compresses the input video signal 28 to the set compression bit rate. At the same time, the compression encoder 29 writes the compressed data 31 into the transmission-side buffer memory (FIFO memory) 33 with the clock 32. This writing is a burst writing depending on the state of the compression processing in the compression encoder unit 29.

A read signal generator 37 detects that a predetermined amount of the compressed data 31 has been stored in the FIFO memory 33 by counting the input clock 32, and generates a continuous read signal 35. Are read out at a constant rate. This reading rate is the same as
This is the compression bit rate set by the PU 45. Therefore, in the FIFO memory 33, no empty or overflow of the data storage amount occurs. This makes it possible to obtain continuous compressed data 34 at a predetermined rate from the FIFO memory 33. That is, this FI
The FO memory 33 has a function of converting the burst data 31 output from the compression encoder unit 29 into continuous compressed data 34 at a predetermined rate.

Next, the system stream generating unit 36
The compressed data 34 of the predetermined rate and the read signal 35 are inputted, and each PSC (Picture Start Cod
e) and the PCR (Program Clo
ck Reference) or SCR (System Clock Reference)
Reference time information obtained by sampling a reference time referred to as a reference time is added and output to the transmission path 39 as a system stream 38. Here, the reference time is determined by the STC (System
Time Clock). The PSC is compressed data 3
4 shows a break of each picture. In addition, the time stamp information indicates that each picture is stored at any time at the video delay time control information (video buffer control information) on the decoder side.
A ring verifier delay (vbv_delay) is referred to as a buffer (hereinafter, referred to as vbv_buffer) 46, and is time information indicating whether to read out from the receiving buffer memory. Then, by defining this read time, the decoder
It is possible to prevent overflow and underflow of the vbv_buffer 46 on the (reception) side.

That is, the time stamp information has an important function for realizing a smooth decoding continuously. Since this time stamp information is information indicating a predetermined point in time of the reference time, the decoder side performs S
Reference time information called TC is also required. That is,
The STC and the time stamp information are compared, and when they match, the reading of the vbv_buffer 46 is started. As described above, according to the MPEG2 standard, STC is used on the encoder side.
And the PCR or SC that sampled the value
R is added to the system stream, and the STC is reproduced on the decoder side based on this information.

On the other hand, the system stream analysis unit 41
The processing operation reverse to that of the system stream generation unit 36 is performed. That is, from the transmission path 39, the system stream 4
0, the compressed data 44 and the time stamp information 6
0 and STC 61 reproduced from SCR or PCR are output. Then, the compressed data 44 of the predetermined rate is vb
The data is output to a FIFO memory called v_buffer 46.
Note that the name of this vbv_buffer is defined in the MPEG standard. At this time, the write signal generator 43 inputs the compressed data 44 and the clock 42 related thereto, and writes the PSC (P
ictureStart Code) is detected, and a write signal 47 is generated from the detected picture segment so that writing to the vbv_buffer 46 is possible.

Next, a vbv_buffer read signal generator 53
Inputs the time stamp information 60 and the STC 61,
After the delay until the TC 61 matches the time stamp information 60, the generation of the read signal 48 of the vbv_buffer 46 is started. Basically, the clock 5 from the compression decoder unit 50
2 is gated until the start of the generation of the read signal, and thereafter, the clock 52 is output as it is as the read signal 48. The clock 52 from the compression decoder unit 50 is a burst clock that basically depends on the processing status of the compression decoder unit 50. Therefore, this vbv_
The buffer 46 is a FIFO memory 33 on the encoder side.
It has the opposite function. The compression decoder unit 50 has a vbv_buff
The compressed data 49 from the er 46 is input at the burst clock 48, decoded, and output as a video signal 51.

[0008] Here, the above-described vbv_buffer 46 shown in FIG.
Will be described in detail. Figure 3 shows the vbv_buffer
An example of a change in the accumulation amount in 46 is shown. The vertical axis represents the accumulated amount, and the horizontal axis represents time (corresponding to STC of the reference time).
The scale on the horizontal axis is the picture display interval of the video signal.
(Or frame period: 33.3 ms) is set as one scale. For convenience of explanation, the compression rate is 6.7 Mbp.
Assume s. First, the write signal generator 43 generates a PSC (Picture_S) in the compressed data 44 which is a video stream.
(tart_Code) 61 is detected, and the time when writing to the vbv_buffer 46 is started from the detected picture break is time (−8). Next, the vbv_buffer read signal generator 53 receives the time stamp information 60 and the STC 61, is delayed until the STC 61 matches the time stamp information 60, and the time when the generation of the read signal 48 of the vbv_buffer 46 is started is time (0). It is. That is, the time indicated in the time stamp information 60 indicates the time (0).

In the example shown in FIG. 3, the time from the first writing to the vbv_buffer 46 to the beginning of reading is 266.4.
ms (= 33.3 ms × 8). During this period, the accumulated amount increases steadily. The slope in this case matches the compression bit rate of the compression encoder unit 29 of 6.7 Mbit. The increase in the accumulation amount is the same in other periods. As described above, the time stamp information 60 stores the compressed data in vbv_bu before the compression decoder unit 50 starts processing.
It can also be said that it indicates the time for accumulation in the ffer 46. The purpose is to prevent the vbv_buffer 46 from generating an empty or overflow with respect to burst reading of the compression decoder unit 50. Therefore, as shown in FIG. 3, the maximum value of the vbv_buffer size (1.8 Mbit)
It is common to initially store up to the vicinity. Note that this vb
The maximum value of v_buffer size is ISO / IEC 1117
2-2, standardized by ISO / IEC 13818-2.

Next, at time (0), the compression decoder unit 50 starts burst reading. In the graph of FIG.
As an extreme example, a case is shown in which the code amount for one picture is read at a time at each picture interval. That is, picture 0 at time (0), picture 1, time (2) at time (1)
.., And reads out the code amount of picture n at a time (n) at a time. This is ISO / IEC 1117
2-2, ISO / IEC 13818-2. As described above, writing and reading of the compressed data to and from the vbv_buffer 46 are performed, and the change in the accumulated amount is as shown in FIG. Note that, as shown in FIG. 3, there is a difference in the code amount for each picture because it depends on the compression mode of each picture. In general, in MPEG, there are pictures compressed in three types of modes: I picture, P picture, and B picture, and the I picture has a much larger code amount than other P pictures and B pictures. FIG. 4 shows a picture configuration in the video stream in the case of FIG. Picture 0 is an I picture, and the picture B repeats in the order of a B picture, a B picture, and a P picture. The picture n is an I picture. Then, as shown in FIG. 3, the I picture is usually the first picture at the start of storage.

[0011]

As described above, in the prior art, at the writing speed depending on the compression bit rate,
This accumulation time was always necessary in order to start the decoding process after the initial accumulation near the maximum value of the size of vbv_buffer. In FIG. 3, the compression bit rate is set to 6.7 Mbps for convenience of explanation. However, in a general MPEG system, the compression bit rate is set to 4 Mbps. Therefore, the accumulation time is about 450 ms as described below. (1.8 × 1,000,000) ÷ 4 × 1,000,000 = 450 ms However, (1.8 × 1,000,000) indicates the maximum value of the size of the vbv_buffer 46. This time corresponds to the compression encoder unit 2 in FIG.
9 occupies most of the delay time from the input of the video signal to the output of the video signal from the compression decoder unit 50. In the case of negotiating in real time by two-way communication like a news program of a broadcasting station, this delay time is fatal. That is, a smooth conversation cannot be realized due to the delay time. Also, even in one-way communication, in a system (remote operation system) that performs some operation based on the received video signal, naturally,
This delay time becomes a problem. The present invention has been made in view of the above problems, and enables a reduction in delay time in vbv_buffer, which occupies most of the entire delay time. A transmission device is provided.

[0012]

According to the present invention, in order to achieve the above object, in transmission of a compressed video signal, a transmitting side compresses compressed data at a predetermined compression bit rate.
Writing to the transmission side buffer memory at the compression bit rate and reading intermittently at the transmission rate of the transmission path faster than the compression bit rate by a predetermined speed, the compressed data includes reference time information, the compression bit rate and the transmission rate. A predetermined time stamp information calculated from the relationship is added and transmitted to the transmission line, and the receiving side intermittently writes the compressed data fetched from the transmission line into a receiving side buffer memory at the transmission rate, Based on the extracted reference time information and the predetermined time stamp information, the compressed data is read from the receiving buffer memory at a speed corresponding to the compression bit rate, and the compressed data is decoded. It is.

The transmitting side adds reference time information and time stamp information to the compressed data, and sends the compressed data to the transmission line. The receiving side performs the above-mentioned processing based on the extracted reference time and the time stamp information. In a video signal transmission device that performs decoding processing of the compressed data captured from a transmission path, a transmitting side includes a compression encoder unit that compresses an input video signal at a predetermined compression bit rate, and temporarily stores the compressed data. A transmitting-side buffer memory for outputting an empty flag indicating whether or not the accumulation state is empty; and intermittently reading the accumulated compressed data at a transmission rate of a transmission path faster than the compression bit rate by a predetermined speed in accordance with the empty flag. A read signal generating unit for generating a read signal for the reference time information; It is obtained by a video signal transmission apparatus having a system stream generator for generating a system stream by adding a predetermined time stamp information calculated from the relationship of the transmission rate and bit rate. Further, on the receiving side, a system stream analyzing unit that extracts and outputs the compressed data, the reference time information, and the predetermined time stamp information from the transmitted system stream, and a receiving unit that temporarily stores the compressed data. A buffer memory, a write signal generator for generating a write signal to the receiver buffer memory, a compression decoder for decoding the compressed data output from the receiver buffer memory and outputting a video signal, A receiving buffer memory controller for generating a read signal to the receiving buffer memory based on the reference time and the predetermined time stamp information.

The present invention makes it possible to transmit data to the receiving side at a speed higher than the compression bit rate without causing a failure in the stream input in the receiving-side compression decoder section by the above configuration, which has been a conventional problem. In addition, the initial storage time for vbv_buffer, which is a buffer memory on the receiving side, is shortened to enable application to bidirectional communication and a remote control system. For this reason, the transmission side needs to transfer data to the system stream generation unit at a speed faster than the compression bit rate. Therefore, the FIFO memory serving as the transmission side buffer memory is temporarily empty. Therefore, the read signal generation unit on the transmission side monitors the empty flag of the FIFO memory, and performs control to stop reading the FIFO memory when the FIFO memory is empty. On the other hand, on the receiving side, writing to the vbv_buffer is performed at a speed higher than the compression bit rate, and therefore, the data is stored at a higher rate than originally expected. Therefore, if the time stamp information for controlling the reading of the vbv_buffer remains at its original value, an overflow will obviously occur in the vbv_buffer. Therefore, in the present invention, the time stamp information is a value calculated from the compression bit rate and the rate given to the compressed data on the transmission path. As a result, even if data is transmitted to the receiving side at a rate higher than the compression bit rate,
(Decoder side) system stream analysis unit, write signal generation unit, vbv_buffer, vbv_buffer read signal generation unit, compression decoder unit, with the same operation as before, without generating overflow or underflow in vbv_buffer,
The stream can be transferred to the compression decoder section, and the initial accumulation time for vbv_buffer, which has conventionally been a problem, can be significantly reduced.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG. FIG. 1 shows a configuration including a transmission unit, a reception unit, and a transmission path. The transmission unit converts the input video signal 1 into
A compression encoder unit 2 for compressing to a predetermined compression bit rate and outputting compressed data 5 and a clock 6 related to the compressed data 5 and setting data 4 for setting the compression bit rate of the compression encoder unit 2 are generated. CPU3 to do
And a FIFO buffer which is a transmission-side buffer memory capable of temporarily storing the compressed data 5 by a clock 6 and outputting an empty flag 8 when the storage state is empty.
Based on the O memory 7 and its empty flag 8, the FI
A read signal generator 12 for generating a read signal 9 in the FO memory 7; an output data 10 of the FIFO memory 7; a read signal 9 from the read signal generator 12; data 4 indicating a compression bit rate from the CPU 3; Based on the data 70 indicating the transmission rate of the transmission path with respect to the rate, the sampling information of the reference time and the data 4, 7
The system stream generation unit 11 generates a system stream 13 by adding the time stamp information calculated from 0 to the compressed data 10. On the other hand, the receiving unit is the same as the above-described conventional example (FIG. 2), and thus the description is omitted.

Next, the operation of the embodiment shown in FIG. 1 will be described. For convenience of explanation, the transmission capacity of the transmission path 14 is 26.
8 Mbps, and the compression rate is assumed to be 6.7 Mbps. This 26.8 Mbps corresponds to, for example, a case where a band is secured by ATM. First, as initial processing, the compression rate in the compression encoder unit 2 is set to 6.7 Mbps based on the setting data 4 from the CPU 3. The compression encoder 2 converts the input video signal 1 into
Compressed to the set 6.7 Mbps, and the compressed data 5
And its clock 6 are output. At this time, the content of the video stream of the compressed data 5 to be output is the same as that described with reference to FIG. Next, when the read signal generation unit 12 detects that the writing of data to the FIFO memory 7 has been started based on the empty flag 8, the read signal generation unit 12
, A read signal 9 is generated, and the FIFO memory 7 is set to a read state. The reading speed in this case is 26.8 Mbps, which is the above transmission rate. And FIFO
The compressed data 10 read from the memory 7 is input to the system stream generator 11 together with the read signal 9.

In the system stream generation unit 11, the CP
The data 4 indicating the compression rate from U3 and the data 70 indicating the transmission rate on the transmission line for the compressed data are input, and the sampling information of the reference time and the time stamp information calculated from the data 4 and 70 are added to the compressed data 10. , A system stream 13. In this case, since the read speed of the FIFO memory 7 is 26.8 Mbps while the compression rate is 6.7 Mbps,
In the FO memory 7, data is intermittently generated. I will explain this point in more detail. In general, the data written in the FIFO memory 7 is such that the first picture is an I picture as shown in FIG.
The amount is close to the vbv_buffer size.

Therefore, in the FIFO memory 7, 1
A large amount of data is written at a high speed in a time corresponding to a picture (about 33.3 ms), and the read operation at 26.8 Mbps does not become empty for a while. Then, in the subsequent P and B pictures, since the code amount is smaller than that in the I picture, the FIFO memory 7 eventually becomes empty. Therefore, based on the empty flag 8 generated from the FIFO memory 7 at this time, the read signal generator 12
The read signal 9 is made inactive so that no data is read, and when the data is written and becomes empty, the read signal 9 is read at 26.8 Mbps so that the data is read until it becomes empty. Activate.

Next, a description will be given of the contents of calculating the time stamp information from the data 4 and the data 70 in the system stream generator 11. If the calculated time stamp information is “new time stamp information” and the conventionally used time stamp information is “conventional time stamp information”, the following equation (1) is obtained. New time stamp information = (conventional time stamp information−reference time) × (data 4 / data 70) + reference time (1) Here, (conventional time stamp information−reference time) is as shown in FIG. To explain with an example, 0 − (− 8) = 8. That is, the conventional time stamp information is “0” in the example of FIG.
Shows the time.

The system stream generator 1
When the above calculation is performed at 1, the time substantially corresponds to the time when the head of the picture is to be output to the transmission line 14, and the reference time at that time is "-8". Here, (data 4 / data 70) is a conversion ratio of the storage time generated for transmitting faster than the compression rate. In this example, 6.7 / 2
6.8 = 1/4. That is, by adding the reference time to (conventional time stamp information-reference time) × (data 4 / data 70), new time stamp information for transmission at a speed higher than the compression rate can be obtained. For example, if the compression rate is 6.7 Mbps and the transmission rate is 26.8 Mbps, from the above equation (1),
The new time stamp information is as follows. New time stamp information = (0-(-8)) x (1/4) +
(−8) = − 6 The above is an explanation of the overall operation in the present invention. The operation of the vbv_buffer 46, which is the buffer memory on the receiving side,
This will be described in more detail with reference to FIG. FIG. 5 is a scale similar to FIG. First, as in FIG. 3, time (-8)
Then, it is assumed that writing of the compressed data to the vbv_buffer 46 is started. Here, as described above, reading from the vbv_buffer 46 starts at time (−6) based on the new time stamp information calculated by Expression (1). However, as described above, since the FIFO memory 7 of the transmission unit becomes intermittently empty after a certain time, averaging that part, the vbv_buffer 46 has a transmission rate of 26.8 Mbps.
Naturally, the writing speed becomes lower. That is, in FIG. 5, since the writing speed for each picture display interval is averaged and displayed, the writing gradient after a certain time is 26.8.
Mbps lower than the slope of the transmission unit.
This depends on the occurrence status of the empty in the IFO memory 7. Note that the burst property of data reading in the vbv_buffer 46 is the same as the conventional one as shown in FIG.

However, since the transfer on the transmission line 14 is a burst transfer at a maximum of 26.8 Mbps with respect to the compression bit rate of 6.7 Mbps, the buffer is conventionally stored in the FIFO memory 7 of the transmission unit. The data that has been processed is buffered in the vbv_buffer 46 of the receiving unit. For this reason, in FIGS. 3 and 5, the accumulated amount of the corresponding picture at the time of reading is always larger in FIG. 5 than in the conventional FIG. Therefore, there is a concern that overflow occurs in the vbv_buffer 46. However, F
Since the capacity of the IFO memory 7 and the capacity of the vbv_buffer 46 are approximately equal, the size of the vbv_buffer that is twice the
If v_buffer 46 is reserved, the technical problem in this respect can be solved. As described above, in the present embodiment, the initial accumulation time in the vbv_buffer is reduced from 266.4 ms to 1/4 of 66.6 m, as compared with the conventional example shown in FIG.
s. Further, in the present embodiment, the compression bit rate is set to 6.7 Mbps for the sake of explanation, but if the commonly used 4 Mbps is applied, the reduction ratio of the initial storage time in the vbv_buffer can be further increased.

[0022]

According to the present invention, it is possible to shorten the delay (accumulation) time in the vbv_buffer which occupies most of the delay time by the video signal transmission apparatus, and it has been impossible to adapt the conventional bidirectional communication system or remote control system. Can be provided. Further, since the present invention can be realized by time stamp information of a system stream that can include audio data and private data, the present invention can be realized by many applications.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a system configuration of the present invention.

FIG. 2 is a block diagram showing an example of a conventional system configuration;

FIG. 3 is a diagram showing a change in an accumulation amount in a vbv_buffer 46 according to the related art.

FIG. 4 is a diagram showing a picture configuration in a video stream.

FIG. 5 is a diagram showing a change in an accumulation amount in a vbv_buffer 46 in the present invention.

[Explanation of symbols]

1: compression encoder, 7: FIFO memory, 11: system stream generator, 12: read signal generator, 1
4: transmission path, 41: system stream analysis unit, 43:
Write signal generator, 46: vbv_buffer, 50: compression decoder, 53: vbv_buffer read signal generator.

Claims (3)

[Claims] In a transmission of a compressed video signal, a transmission side writes compressed data compressed at a predetermined compression bit rate into a transmission side buffer memory at the compression bit rate, and transmits the data at a predetermined speed higher than the compression bit rate. While reading intermittently at the transmission rate of the channel, the compressed data, the reference time information, and the predetermined time stamp information calculated from the relationship between the compression bit rate and the transmission rate is added and transmitted to the transmission line, On the receiving side, the compressed data fetched from the transmission path is intermittently written into the receiving buffer memory at the transmission rate, and based on the extracted reference time information and the predetermined time stamp information, the receiving buffer memory And reads the compressed data at a speed corresponding to the compression bit rate, and decodes the compressed data. A video signal transmission method characterized by performing processing. 2. A transmitting side adds reference time information and time stamp information to the compressed data, and sends the compressed data to a transmission path. At a receiving side, based on the extracted reference time and the time stamp information, In a video signal transmission device that performs decoding processing of the compressed data captured from a transmission path, a transmitting side includes a compression encoder unit that compresses an input video signal at a predetermined compression bit rate, and temporarily stores the compressed data. A transmitting-side buffer memory for outputting an empty flag indicating whether or not the accumulation state is empty; and intermittently reading the accumulated compressed data at a transmission rate of a transmission path faster than the compression bit rate by a predetermined speed in accordance with the empty flag. A read signal generating unit for generating a read signal for the reference time information; A video signal transmission apparatus, comprising: a system stream generation unit that generates a system stream by adding predetermined time stamp information calculated from the relationship between the transmission rate and the transmission rate. 3. The video signal transmission device according to claim 2, wherein the compressed data, the reference time information, and the predetermined time stamp information are extracted and output from the transmitted system stream to a receiving side. An analyzing unit, a receiving buffer memory that temporarily stores the compressed data, a write signal generating unit that generates a write signal to the receiving buffer memory, and a compressed data output from the receiving buffer memory. A compression decoder unit that decodes and outputs a video signal, and a receiving buffer memory control unit that generates a read signal to the receiving buffer memory based on the extracted reference time and the predetermined time stamp information. A video signal transmission device characterized by the above-mentioned.