JPH11205789A - Transmission rate converter of mpeg2 transport stream - Google Patents

Abstract

PROBLEM TO BE SOLVED: To output an MPEG(moving picture experts group) 2 transport stream inputted by an optional transmission rate to another optional transmission rate without damaging its contents. SOLUTION: The MPEG 2 transport stream inputted to a packet identifying circuit 2 through a synchronization detection protecting circuit 1 has ID of a packet identified there. The packet of the stream has packets excepting for null packets select-controlled by a program clock reference(PCR) extracting circuit 3 and housed in a buffer 9. A PCR extracting circuit 3 extracts a PCR value from a packet including PCR and allows a PLL circuit 4 to reproduce the system clock of 27 MHz from the PG value. A packet reading circuit 5 reads the packet from the buffer 9 by an output transmission rate and supplies it to a PG replacing circuit 7, which replaces the PCR value of the supplied packet with a PG value outputted from the circuit 4 to supply for an output circuit 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an MPEG2 transport stream transmission system, and more particularly, to an MPEG2 transport stream (single program) input at an arbitrary transmission rate without deteriorating its contents. The present invention relates to an MPEG2 transport stream transmission rate conversion device for converting a transmission rate into an output.

[0002] MPEG (MPEG) is an international standard for compressing and decompressing digital moving pictures. MPEG (Moving) is a subordinate organization of the International Organization for Standardization (ISO).
Picture Experts Group).

[0005] MPEG is not a moving picture standard for CD-ROM, but MPEG1 is designed so that FMV can be displayed at a data reading speed from CD-ROM.

[0004] MPEG1 has been defined with consideration for reading and reproducing from a CD-ROM.
Image quality that can be realized at a data transfer rate of about 1.5 megabits per second, which is the standard readout speed.

[0005] MPEG2 is a standard corresponding to a higher data transfer rate (10 to 100 megabits).
It is a higher quality standard than MPEG1.

[0006] Also, MPEG4 corresponding to a data transfer rate lower than that of MPEG1 is being separately established (MP
EG3 was merged with MPEG2 in the middle of the work) (Toshiharu Nishizawa, "Multimedia Glossary", November 10, 2006, Ohmsha).

With regard to media multiplexing, which is a basic function of the MPEG system, there are two methods of multiplexing a compression-encoded audio or video bit stream into one stream: bit multiplexing and packet multiplexing.
A typical example of the former is ITU-T Recommendation H, 221, which is used for video conferences and video telephone systems based on international standards.

On the other hand, the multiplexing method used in the MPEG system is based on packet multiplexing, and the present invention relates to this packet multiplexing method.

In the multiplexing example of the MPEG1 system which is packet multiplexing, encoded individual streams (elementary streams) of video, audio, data, etc. are arranged in units of 8 bits (1 byte) and have variable lengths. In a packet with a length of. At the beginning of the packet, a 24-bit packet start code prefix indicating the start of the packet, a stream ID for identifying the type of media, a packet length, and a time stamp for decoding and presentation are arranged.

[0010] Furthermore, packets such as video, audio, data, and the like are collected for approximately the same amount of time to form a pack. The head of the pack includes a 32-bit pack start code, a system clock reference SCR for generating a reference time, and the like.

As described above, in packet multiplexing, synchronization of media separation is ensured by a packet header, and media identification is performed by information in the header.

Also, the transmission rate for each medium can be flexibly changed according to the multiplexing ratio. Note that these start codes are the start codes (sequence, GOP, picture,
Slices) and a common framework.
Care must be taken to avoid incorrect start code recognition (emulation).

When decoding and playing back audio and video that have been compression-encoded, sound and video must be synchronized. In the MPEG system standard, high-precision synchronization is achieved by multiplexing time (time stamp) information for reproducing audio and video in a packet header on the encoder side. The time stamp is given to an access unit, that is, a unit of audio and video encoding (corresponding to an audio frame in the case of audio and a picture in the case of video), and has an accuracy of 1/90.
kHz. Two types of time stamps are defined: a presentation time stamp (PTS) that gives the presentation time of audio and video, and a decoding time stamp (DTS) that gives the decoding start time.

In a synchronous system using a time stamp, the demultiplexer on the decoder side separates each encoded stream of audio and video from the multiplexed stream, and also separates each PTS. The time stamp comparison unit calculates the difference between the respective PTSs, and delays either the audio or video decoding output according to the result to synchronize them. At this time, different delays occur in the audio and video decoders, but there is no problem if control is performed in the delay buffer including the delay difference. In actual hardware, the delay of the decoder output increases the amount of memory, so that it is general to delay and synchronize the encoded stream.

[0015] Further, as the reference time of the PTS and the DTS,
A system time clock (STC) of 90 kHz in the MPEG1 system standard and 27 MHz in the MPEG2 system standard is provided in the encoder and the decoder.
The STC of the decoder is connected to the STC of the encoder by PLL (Ph
As a time stamp for synchronizing, a system clock reference (SCR) and a program clock reference (P
CR; MPEG2 system only) is defined.

To ensure that the PLL operates stably, the transmission interval of the SCR is 700 ms or less.
The transmission interval of R is set to 100 ms or less. Furthermore, in the transport stream described below,
Video and audio playback sampling frequency is STC
It must be synchronized to 27 MHz.

In the MPEG2 system, a plurality of videos,
A transport stream (TS) as a stream multiplexing a plurality of programs composed of audio and data
And a program stream (PS). A packetized elementary stream (PES) packet, which is a basic element constituting both streams and is an intermediate stream for enabling a change between the two streams, is defined.

The TS packet is a fixed-length packet of 188 bytes, and its structure is shown in FIG. This length is AT
Taking into account the compatibility with the M cell length and the applicability in performing error correction coding such as Reed-Solomon codes, the decision was made at the New York meeting in July 1993.

[0019] As shown in FIG.
It consists of a fixed-byte packet header, a variable-length adaptation field, and a payload. The adaptation field below the packet header and the presence or absence of the payload are indicated by an adaptation field flag (2 bits) in the header. The adaptation field has a function of transmitting information such as PCR and a stuffing function. The PID is a number for identifying a packet, and is composed of 13 bits. One PE
The S packet is divided into payloads of a plurality of TS packets having the same PID number and transmitted. The head of the PES packet is inserted so as to start from the head of the payload of the TS packet. The transport scrambling control (2 bits) indicates the presence or absence of scrambling for the TS payload (the above-mentioned "MPEG", edited by The Institute of Television Engineers of Japan, Ohmsha, Apr. 20, 2008).

[0020]

2. Description of the Related Art Recently, MPEs have been used in video distribution systems.
There is a demand for a system using the G2 compression system, and among them, the transmission system of the MPEG2 transport stream is often used between transmission lines where errors occur.

However, when considering the case of transmitting signals at different transmission rates between the transmission devices,
Unlike the conventional digital signal, the signal of the MPEG2 transport stream also transmits time information called PCR, and a conventional transmission rate converter having only a buffer outputs the jitter standard of the PCR of the MPEG2 transport stream signal. May not be satisfied.

Although the signal of the MPEG2 transport stream must be a continuous packet, a conventional transmission rate converter having only a buffer has the following problems.
The continuity cannot be ensured.

The following first to fourth prior arts have been proposed as conventional examples regarding the transmission system of the MPEG2 transport stream.

First, a transmitting apparatus and a receiving apparatus disclosed in Japanese Patent Application Laid-Open No. 8-149428, which is cited as a first prior art, transmits an MPEG transport stream using a transmission path conforming to IEEE-P1394. For the purpose of accurate transmission, a transport stream is packetized in a P1394 interface and output to a transmission path conforming to IEEE-P1394, while a PCR detection circuit detects a PCR from an MPEG transport stream. , The absolute time at the timing when it is detected by the sync time providing circuit is added to the packet.

Japanese Patent Application Laid-Open No. Hei 8 (1996) is cited as a second prior art.
A data transmission / reception device disclosed in Japanese Patent Application Laid-Open No. 195723/1995 is a system for transmitting an MPEG2 data stream by time compression, which aims to be able to be shared with a time division multiplexing system. The system compares the PCR value of the compressed data packet with a value obtained by multiplying the system clock by a compression ratio, creates a system clock by PLL, forms a PCR, and replaces the PCR value of the time-compressed data packet with that value. At the time of data recording, the transmitted PCR value is compared with a value obtained by multiplying the system clock by a compression ratio, a system clock is formed by a PLL to form an ATS, and this ATS value is inserted.
During playback, playback is performed at a speed corresponding to the compression ratio of time compression.
The playback time is controlled using the TS.

Japanese Patent Application Laid-Open No. Hei 9 as a third prior art
A digital signal transmission device and a recording device disclosed in Japanese Patent No. 46390/2004 provide a transmission device and a recording device that do not require internal analysis of a digital signal, and prevent a buffer on the receiver side from overflowing or underflowing. For the purpose of controlling on the transmission side, each MPEG2
The arrival timing when the data packet is output to the transmitter is acquired by an arrival timing acquisition device, the time stamp generator latches the value of CTR at the arrival timing, and furthermore, the maximum delay time between a predetermined transmitter and a receiver. A transmission time stamp is generated by adding the count value of the data packet, and the input data packet is converted into a source packet by adding a transmission time stamp by a time stamp adding device, and a plurality of source packets are collected by a transmission packet converter. It is configured to be converted into a transmission packet and transmitted.

Japanese Patent Application Laid-Open No. Hei 9 as a fourth prior art
The MPEG2 data transfer device disclosed in JP-A-116563 discloses an MPE using a transport packet method.
An object of the present invention is to provide an MPEG2 data transfer apparatus for greatly reducing the processing time for transferring G2 data to an ATM line and performing a stream process for accurately reproducing the data with respect to time, and transferring the MPEG2 data to an ATM board. Therefore, the MPEG2 data is transferred from the PCI bus, the MPEG2 data is stored in the temporary storage unit by the address designation by the address control circuit, and at the same time, the extracting unit extracts the synchronization standard time (PCR) of the MPEG2 data, and stores the PCR in the PCR storage unit. And MPU is PC
The time interval between R is calculated, the MPEG2 data is read from the temporary storage unit according to the interval, and is transferred to the ATM board.
It is configured to speed up the transfer to the line.

[0028]

However, none of the above-mentioned prior art examples 1 to 4 discloses any technique for converting the transmission rate of the MPEG2 transport stream.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been made in order to solve the above-mentioned problems inherent in the prior art. Therefore, an object of the present invention is to provide an MPEG2 transport signal input at an arbitrary transmission rate. A new MPE that can convert a stream (single program) to any other transmission rate without losing its contents and output it
An object of the present invention is to provide a G2 transport stream transmission rate converter.

Another object of the present invention is to provide a novel MPEG2 transport stream transmission rate conversion apparatus which can easily ensure the continuity of signals of an MPEG2 transport stream.

[0031]

In order to achieve the above object, an MPEG2 transport stream transmission rate converter according to the present invention comprises: a synchronization detection protection circuit for an input MPEG2 transport stream;
A packet ID identification circuit for identifying the packet ID of the transport stream, a buffer for storing the packet identified by the packet ID identification circuit,
A PCR extraction circuit for extracting a CR, a PLL circuit for reproducing a system clock of 27 MHz from a PCR value extracted from the PCR extraction circuit, a packet reading circuit for reading a packet stored in the buffer at an output transmission rate; If the packet read from the packet is a packet including a PCR, a PCR value changing circuit for changing the PCR value to the PCR data output from the PLL circuit, and a packet output from the PCR value changing circuit are supplied to the MPEG2 And an output circuit that outputs the transport stream.

The packet ID identification circuit is further characterized in that it identifies a packet as a NULL packet, a packet including a PCR, or a packet other than each of the above packets.

The PCR extraction circuit is further characterized in that a packet other than a NULL packet is selected and write control is performed on the buffer.

The packet reading circuit is further characterized in that it generates an MPEG2 transport timing of an input format and reads a packet from the buffer in accordance with the timing.

The packet reading circuit is further characterized in that, if the packet read from the buffer is not a packet including a PCR, the packet is directly supplied to the output circuit.

Further, N which generates a NULL packet
A UL packet generation circuit is provided between the packet readout circuit and the output circuit, and the NULL packet is supplied to the output circuit as necessary, thereby ensuring the continuity of the MPEG2 transport stream.

The output circuit selectively obtains a packet read from the buffer and a NULL packet output from the NULL packet generation circuit, and
It is output as a G2 transport stream.

[0038]

Next, a preferred embodiment of the present invention will be described in detail with reference to the drawings.

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

Referring to FIG. 1, the MPEG according to the present invention
The two-transport-stream transmission rate converter identifies the synchronization detection protection circuit 1 of the input MPEG-2 transport stream (single program) and whether the packet is a NULL packet, a packet containing PCR, or another packet. An ID identification circuit 2 for identifying a packet ID; a PCR extraction circuit 3 for writing a packet other than a NULL packet into the buffer 9 to extract a PCR value from a packet including a PCR;
A PLL circuit 4 for reproducing a system clock of 27 MHz from the PCR value extracted from the extraction circuit 3, and an MPEG2 transport timing of an input format at an output transmission rate, and packet reading for reading a packet from a buffer 9 in accordance with the timing. Circuit 5 and NU
A NULL packet generation circuit 6 for generating and outputting an LL packet;
Value changing circuit 7 for changing the PCR value to the PCR data output from the PLL circuit 4 in the case of a packet including
An output circuit 8 for selecting a packet read from the buffer 9 and a NULL packet output from the NULL packet generation circuit 6 and outputting the selected packet as an MPEG2 transport stream; And a buffer 9 for storing the data according to the write control signal.

Next, the operation of the embodiment according to the present invention will be described. When an MPEG2 transport stream (single program) is input to the synchronization detection protection circuit 1, the synchronization of the MPEG2 TS is detected there. Protected. Next, the packet ID identification circuit 2
The PID (packet identifier, see FIG. 4) of the packet is identified.

The packet identified by the packet identification circuit is supplied to the PCR extraction circuit 3 and the buffer 9,
The CR extraction circuit 3 writes a packet other than the NULL packet into the buffer 9 under the control of the write control signal, extracts a PCR value from the packet including the PCR, and supplies it to the PLL circuit 4. The PLL circuit 4 reproduces and outputs a 27 MHz system clock based on the PCR value supplied from the PCR extraction circuit 3.

On the other hand, the packet extraction circuit 5 outputs the M of the input format at an arbitrary output transmission rate supplied from the outside.
A PEG2 transport timing is generated, and a packet stored in the buffer 9 is read in accordance with the generated timing.

In the case of a packet including a PCR among the packets read by the packet reading circuit 5, P
The signal is input to the CR replacement circuit 7 and the P
The CR value is replaced with the PCR value output from the PLL circuit 4. In the case of a packet that does not include a PCR among the read packets, the packet reading circuit 5 directly supplies the packet to the output circuit 8.

Each packet output from the packet read circuit 5 and the PCR replacement circuit 7 is output from the output circuit 8 to the output MP
It is output to the transmission path as an EG2 transport stream.

The signal of the MPEG2 transport stream needs to be a continuous packet. However, for example, when no packet is stored in the buffer 9, the stream signal may be interrupted.
Therefore, in order to ensure the continuity, the NULL generated by the NULL packet generation circuit 6 as necessary.
The L packet is supplied to the output circuit 8.

[0047]

Next, preferred embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a flowchart of an input system showing an example of the operation of the present invention, and FIG. 3 is a flowchart of an output system showing an example of the operation of the present invention.

[First Embodiment] Referring to FIGS. 1, 2 and 3, in the first embodiment in which the output transmission rate is higher than the input transmission rate, the synchronization detection protection circuit 1 It is determined whether or not the data format is the MPEG2 transport stream based on the packet header signal, the packet sync signal, and the packet data enable signal of the input MPEG2 transport stream (single program), and further, the DVB (Digital Video)
o Broadcasting) to determine whether the format is 188 or 204, and performs data synchronization detection protection (step S1).

The packet data detected synchronously is determined by a packet ID identifying circuit 2 for identifying the packet ID, whether the packet ID is a NULL packet or a packet including a PCR,
Or other packets (step S
2). If the identification result indicates a NULL packet, the packet is discarded (step S3).

The packets other than the identified NULL packet are sent to the PCR extraction circuit 3 for writing to the buffer and extracting the PCR value, and are written to the buffer 9 (step S5). The packet including the PCR is sent to the PCR extraction circuit 3 for extracting the PCR value, and the PCR value is extracted (step S4). The PLL circuit 4 reproduces a 27 MHz system clock based on the extracted PCR value (step S6).

The packet reading circuit 5, which reads packets from the buffer 9 at the output transmission rate, generates an MPEG2 transport stream timing of the input format at the output transmission rate, and reads the packets from the buffer 9 in accordance with the timing (step S7). . The NULL packet generation circuit 6 also generates a NULL packet in accordance with the timing (step S9).

Among the packets read by the buffer 9, the packet containing the PCR is a PCR data reordering circuit 7.
And the PCR value is 27 MHz output from the PLL circuit 4.
The output is replaced with the PCR value of the system clock reproduction (step S8). If there is no more than one packet stored in the buffer 9 at the time of reading from the buffer 9, the output circuit 8 selects the NULL packet of the NULL packet generation circuit 6 and outputs it as an MPEG2 transport stream (step S1).
0).

[Second Embodiment] In a second embodiment according to the present invention, the transmission rate of the output is lower than the transmission rate of the input, the input MPEG2 transport stream includes NULL packets, and the NULL In the second embodiment in which the output transmission rate is higher than the input transmission rate excluding packets, the synchronization detection and protection circuit 1
A packet header signal of an input MPEG2 transport stream (single program) including a UL packet,
Based on the packet sync signal and the packet data enable signal, it is determined whether or not the data format is an MPEG2 transport stream. Further, it is determined whether or not the DVB is 188 format or 204 format, and data synchronization detection protection is performed (step S1).

The packet data detected synchronously is determined by the packet ID identification circuit 2 for identifying the packet ID, whether the packet ID is a NULL packet or a packet including a PCR,
Or other packets (step S
2). The identified packet is sent to a PCR extraction circuit 3 which writes a buffer and extracts a PCR value.
If it is not a NULL packet, it is written to the buffer (step S5).

The packet including the PCR is sent to the PCR extraction circuit 3 for extracting the PCR value, and the PCR value is extracted (step S4). The extracted PCR value is PLL
Sent to the circuit 4, where the PCR value is 27 MHz
Is reproduced (step S6).

The packet reading circuit 5, which reads packets from the buffer 9 at the output transmission rate, generates the MPEG2 transport stream timing of the input format at the output transmission rate, and reads the packets from the buffer 9 in accordance with the timing (step S7). .

The NULL packet generation circuit 6 also generates a NULL packet in accordance with the timing (step S9). Among the packets read from the buffer 9, the packet including the PCR is a PCR data reordering circuit 7.
Then, the PCR value is replaced with the PCR value of the 27 MHz system clock reproduction and output (step S8).

If there is no more than one packet stored in the buffer 9 at the time of reading from the buffer 9, the output circuit 8 selects a NULL packet of the NULL packet generation circuit 6 and outputs it as an MPEG2 transport stream ( Step S10).

If the output transmission rate is lower than the transmission rate excluding the input NULL packet, the buffer 9
Since the writing of the packet is stopped before the writing becomes over and the content of the input MPEG2 transport stream (single program) cannot be converted to another arbitrary transmission rate without losing the contents, the output transmission rate Needs to be higher than the transmission rate excluding the input NULL packet.

[0061]

The present invention is constructed and operates as described above. According to the present invention, an MPEG2 transport stream (single program) input at an arbitrary transmission rate can be obtained without impairing its contents. It is possible to accurately convert the data to another arbitrary transmission rate, and it is possible to eliminate the case where the jitter standard of the PCR is not satisfied, thereby realizing good and efficient packet multiplex transmission.

According to the present invention, the continuity of the MPEG2 transport stream can be easily ensured.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a processing flowchart of an input system showing an example of the operation of the present invention.

FIG. 3 is a processing flowchart of an output system showing an example of the operation of the present invention.

FIG. 4 is a format diagram of a general transport stream (TS) packet applied to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Sync detection protection circuit 2 ... Packet identification circuit 3 ... PCR extraction circuit 4 ... PLL circuit 5 ... Packet reading circuit 6 ... NULL packet generation circuit 7 ... PCR replacement circuit 8 ... Output circuit 9 ... Buffer 10 ... Crystal oscillator

Claims (7)

[Claims] 1. An input MPEG2 transport stream synchronization detection and protection circuit, and a packet I for identifying a packet ID of the input MPEG2 transport stream.
A D identification circuit; a buffer for storing the packet identified by the packet ID identification circuit; a PCR extraction circuit for extracting a PCR from the packet; and a 27 MHz system clock reproduced from the PCR value extracted from the PCR extraction circuit. A PLL circuit, a packet reading circuit for reading the packets stored in the buffer at an output transmission rate, and a P value output from the PLL circuit when the packet read from the buffer is a packet including a PCR.
A circuit for changing a PCR value to CR data;
MPE supplied with the packet output from the value reordering circuit
An MPEG2 transport stream transmission rate conversion device, comprising: an output circuit that outputs a G2 transport stream. 2. The MPEG2 transport stream according to claim 1, wherein the packet ID identification circuit identifies whether the packet is a NULL packet, a packet including a PCR, or a packet other than each of the packets. Transmission rate converter. 3. The MPEG2 transport stream transmission according to claim 1, wherein the PCR extraction circuit selects a packet other than a NULL packet and controls writing to the buffer. Rate converter. 4. The packet read circuit generates an MPEG2 transport timing of an input format,
The MPEG2 transport stream transmission rate converter according to any one of claims 1 to 3, further comprising reading packets from the buffer in accordance with the timing. 5. The packet reading circuit according to claim 1, wherein the packet reading circuit supplies the packet directly to the output circuit when the packet read from the buffer is not a packet including a PCR. An MPEG2 transport stream transmission rate converter according to claim 1. 6. A NULL packet generation circuit for generating a NULL packet is provided between the packet readout circuit and the output circuit, and supplies the NULL packet to the output circuit as necessary, thereby providing a continuous MPEG2 transport stream. 2. The method according to claim 1, further comprising:
6. The MPEG2 transport stream transmission rate converter according to any one of claims 1 to 5. 7. The output circuit selectively acquires a packet read from the buffer and a NULL packet output from a NULL packet generation circuit, and outputs
7. The MPEG2 transport stream transmission rate converter according to claim 6, further comprising outputting as two transport streams.