JP2010239546A - Transcoder, transcoding method and transcoding computer program, and moving image transmitting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transcoder transcoding input coded moving image data having less delay times. <P>SOLUTION: The transcoder 1 includes: a decoder 12 for decoding each picture contained in first moving image data coded according to a first coding system; a picture-discarding section 14 for discarding the predetermined number of pictures including a first picture that has become a reference for coding other pictures in the first moving image data among the decoded pictures; and an encoder 15 for using a leading picture in the remaining pictures which have not been discarded by the picture discarding section 14, as a picture that serves as a reference for coding the other pictures, and recoding the remaining pictures according to a second coding system. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The embodiment disclosed herein uses a transcoder, a transcoding method, a computer program for transcoding, and a computer program for converting encoded moving image data into moving image data encoded according to another encoding method. The present invention relates to a moving image transmission apparatus.

  In recent years, services for distributing moving image data via an Internet Protocol (IP) network have been provided. One such service is to receive moving image data distributed by broadcast radio waves to areas where it is difficult to receive terrestrial digital television broadcasts, and redistribute the moving image data through the IP network. Service to be considered.

  However, the communication bandwidth that can be used in the IP network is narrower than the communication bandwidth that can be used in broadcast waves. Therefore, a technique has been developed in which the input encoded moving image data is once decoded and the decoded moving image data is encoded again according to an encoding method with higher encoding efficiency (for example, Patent Document 1). reference). In this way, the process of converting moving image data encoded according to a specific encoding method into moving image data encoded according to another encoding method is called transcoding.

JP 2004-96491 A

In addition, in a service that receives moving image data distributed by broadcast radio waves and redistributes the moving image data through the IP network, moving images that are directly distributed by broadcast radio waves to the redistributed moving image data. Data and service and technical identity are required. Therefore, a video re-transmission system that receives moving image data distributed by broadcast radio waves and re-distributes the moving image data is a delay of re-distributed moving image data with respect to moving image data directly distributed by broadcast radio waves. Must be made as small as possible.
For example, the Digital Terrestrial Broadcasting Supplemental Retransmission Screening Committee has formulated terrestrial digital broadcast IP retransmission system screening guidelines that define requirements for moving image data to be retransmitted. This terrestrial digital broadcast IP retransmission system examination guideline stipulates that “the delay of video, audio, and data broadcasts is 2.5 seconds or less for the entire system compared to the reception by radio waves of digital terrestrial television broadcasting”. It has been. Please refer to gideline20071026.pdf published at http://nab.or.jp/shinsakai for terrestrial digital broadcast IP retransmission method examination guidelines.

  Accordingly, an object of the present specification is to provide a transcoder, a transcoding method, a computer program for transcoding, and a moving image transmission apparatus capable of transcoding input encoded moving image data with a small delay time.

  According to one embodiment, a transcoder is provided. The transcoder includes a decoder that decodes each picture included in the first moving image data encoded in accordance with the first encoding method, and another one of the decoded pictures in the first moving image data. A picture discard unit that discards a predetermined number of pictures including the first picture that is a reference for encoding a picture, and a first picture among the remaining pictures that are not discarded by the discard unit As an encoding reference picture, an encoder that re-encodes the remaining pictures in accordance with the second encoding method is included.

  According to another embodiment, a moving image transmission apparatus is provided. The moving image transmission apparatus includes: a receiving unit that receives a video signal in units of packets; a first moving image data encoded by a first encoding method from a video signal; a multiplexer that separates other data; A decoder that decodes each picture included in the first moving image data; and a first picture that is a reference for encoding other pictures in the first moving image data among the decoded pictures. A second coding scheme in which a picture discarding unit that discards a predetermined number of pictures including the first picture among the remaining pictures that have not been discarded by the discarding unit is used as a reference picture for coding other pictures Multiplexes moving picture data including each picture re-encoded in accordance with the second encoding scheme and an encoder that re-encodes the remaining pictures according to Having a multiplexer for creating a packet, an encryption unit for encrypting the packet, and a transmission section for outputting the encrypted packet by.

  According to yet another embodiment, a transcoding method is provided. In this transcoding method, each picture included in the first moving image data encoded according to the first encoding method is decoded, and among the decoded pictures, other pictures in the first moving image data are decoded. A predetermined number of pictures including the first picture that is a reference for encoding the first picture is discarded, and among the decoded pictures, the first picture of the remaining pictures not discarded is replaced with another picture. Includes re-encoding the remaining pictures in accordance with the second encoding method.

  According to still another embodiment, there is provided a transcoding computer program for causing a computer to convert moving image data encoded according to a first encoding method into moving image data encoded according to a second encoding method. Is done. The computer program decodes each picture included in the first moving image data encoded according to the first encoding method, and among the decoded pictures, the other moving image in the first moving image data. A predetermined number of pictures including the first picture that is a reference for encoding are discarded, and among the decoded pictures, the first picture of the remaining pictures that are not discarded is replaced with the other pictures. As a picture serving as a reference for encoding, an instruction for causing the computer to re-encode the remaining picture according to the second encoding method is included.

The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It should be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention as claimed.

  The transcoder, transcoding method, transcoding computer program, and moving image transmission apparatus disclosed in this specification can transcode input encoded moving image data with a small delay time.

1 is a schematic configuration diagram of a transcoder according to a first embodiment. (A)-(c) is a conceptual diagram of the delay time when one picture or two pictures are discarded, respectively, when no picture is discarded. It is an operation | movement flowchart of the transcoding process of the encoding moving image data performed by the transcoder based on 1st Embodiment. It is a schematic block diagram of the transcoder based on 2nd Embodiment. It is a conceptual diagram of the delay time generated by the transcoder according to the second embodiment. It is an operation | movement flowchart of the transcoding process of the encoding moving image data performed by the transcoder based on 2nd Embodiment. It is a schematic block diagram of the transcoder which concerns on 3rd Embodiment. It is a schematic block diagram of a video retransmission system. It is a schematic block diagram of the moving-image transmission apparatus which has the transcoder by any embodiment which the video re-transmission system shown by FIG. 8 has.

Hereinafter, the transcoder according to the first embodiment will be described with reference to the drawings.
This transcoder is the first predetermined number of pictures including pictures that are included in the input encoded moving image data and that have a relatively large amount of encoding calculation and that are referenced as a reference when encoding other pictures. The delay time is shortened by re-encoding.
Note that the picture included in the moving image data to be transcoded may be either a field acquired by the interlace method or a frame acquired by the progressive method.

  FIG. 1 is a schematic configuration diagram of a transcoder 1 according to the first embodiment. As shown in FIG. 1, the transcoder 1 includes a demultiplexer 11, a decoder 12, an encoding start position unit 13, a picture discard unit 14, an encoder 15, a buffer 16, and a multiplexer 17. Each of these units included in the transcoder 1 may be a separate circuit, for example. The transcoder 1 may be an integrated circuit in which circuits having functions of these units included in the transcoder 1 are integrated. Alternatively, each of these units included in the transcoder 1 may be a functional module realized by a computer program executed on one or a plurality of processors included in the transcoder 1.

The demultiplexer 11 separates the multiplexed video signal input to the transcoder 1 into encoded moving image data and other data such as audio signals and captions. Then, the demultiplexer 11 passes the encoded moving image data to the decoder 12. The demultiplexer 11 stores data other than the encoded moving image data in the buffer 16.
Further, the demultiplexer 11 passes the encoding type of each picture included in the encoded moving image data, the data amount of each picture, and the quantization scale to the encoding start position determination unit 13.

The decoder 12 decodes each picture included in the moving image data encoded by the first encoding method received from the demultiplexer 11 by a decoding method according to the first encoding method. For example, if the first encoding method is Moving Picture Experts Group phase 2 (MPEG-2), the decoder 12 performs variable-length decoding on accompanying data such as each picture and motion vector of the encoded moving image data. . Then, the decoder 12 performs an inverse quantization process and an inverse orthogonal transform process on the variable length decoded data. If the picture to be decoded is an I picture by performing the inverse quantization process and the inverse orthogonal transform process, the picture is decoded. On the other hand, if the picture to be decoded is a P picture or a B picture, the decoder 12 adds the predicted image obtained from the corresponding block of the reference picture that has already been decoded to the difference signal obtained by the inverse orthogonal transform process. The picture is decoded by adding.
Note that an I picture is a picture that is encoded by an intra-encoding method that encodes the picture using only information included in one picture to be encoded. On the other hand, a P picture and a B picture are pictures that are encoded by an inter-encoding method that performs encoding using information on pictures before and after the picture to be encoded. Among these, the P picture is encoded using only a picture temporally preceding the encoding target picture. Further, the B picture is encoded using both a picture temporally preceding and a picture temporally subsequent to the picture to be encoded.
The I picture, B picture, and P picture are repeated at a predetermined fixed period. A structure including a plurality of consecutive pictures that are repeated at a certain period and in which an encoding method for each picture is defined is called a group of pictures (GOP).
The decoder 12 decodes each picture in the encoding order according to the GOP structure. Each time a picture is decoded, the decoder 12 sends information indicating the decoded picture and the coding type (that is, I picture, P picture, B picture) of the picture before decoding to the picture discarding unit 14. hand over.

Based on the encoding type of each picture, the data amount of each picture, or the quantization scale, the encoding start position determining unit 13 firstly re-encodes the picture that the encoder 15 re-encodes so that the delay time due to transcoding is minimized The position of the encoded leading picture is determined.
In the GOP, generally, an I picture that serves as a reference for coding other pictures to be inter-coded is arranged at the head in the coding order. Therefore, in order to transcode the encoded moving image data, usually, the decoder first decodes the I picture of each GOP, and then the encoder re-encodes the decoded I picture. In this case, the time required for the decoding process, the encoding process, and the data transmission process for the I picture becomes the delay time due to transcoding.
Moreover, the data amount of the encoded I picture is generally larger than the data amount of the encoded P picture and B picture. For this reason, the time required for the decoding process, encoding process, and data transmission of the I picture is longer than the time required for the decoding process, encoding process, and data transmission of the P picture and B picture.

  Therefore, the encoding start position determination unit 13 discards the first predetermined number of pictures including the I picture from the first GOP of the original moving image data, thereby changing the position of the first picture to be re-encoded. Estimate the delay time. When this transcoder 1 is used in a video re-transmission system that re-distributes a video signal distributed by broadcast radio waves via a communication network, discarding pictures as described above is performed only when the video re-transmission system is activated. Occurs. Therefore, there is no disadvantage associated with discarding pictures other than that the service provision start time is delayed by a very short time corresponding to the number of discarded pictures.

  In order to estimate the delay time, the encoding start position determination unit 13 estimates the decoding start waiting period of the encoded first picture. In this decoding start waiting period, transmission of the first I picture of the original moving image data to the decoder 12 is started, and then transmission of the encoded first picture to the decoder 12 is started according to the GOP encoding order of the original moving image data. This is the period until In addition, the encoding start position determination unit 13 estimates the re-encoding processing period of the encoded head picture when a predetermined number of pictures are discarded. This re-encoding processing period is the time required from the start of transmission of the first I picture of the original moving image data to the decoder 12 until the encoder 15 finishes outputting the re-encoded head picture. . In the re-encoding processing period, a period required for decoding each picture up to the encoding start picture in accordance with the GOP encoding order of the original moving image data, and the encoding start picture is re-encoded by the encoder 15. This includes the time required for Further, in the re-encoding processing period, the period required for the first I picture of the original moving image data to be transmitted from the demultiplexer 11 to the decoder 12 and the decoded encoded top picture from the decoder 12 to the encoder 15 The period required for transmission and the period required for transmitting the re-encoded encoded first picture from the encoder 15 to the multiplexer 17 are included. Then, the encoding start position determination unit 13 sets the difference between the re-encoding processing period of the encoded head picture and the decoding start standby period as a delay time.

  FIG. 2A to FIG. 2C are conceptual diagrams of delay times when one picture and two pictures are discarded when the picture is not discarded, respectively. For simplification, in FIG. 2A to FIG. 2C, the GOP will be described as having an IPPP configuration in which the encoding order matches the image playback order and does not include a B picture. In each of FIG. 2A to FIG. 2C, the horizontal axis represents elapsed time. A graph 201 represents the time required to decode the GOP of the original moving image data encoded by the first encoding method input to the transcoder 1. Each vertical line in the graph 201 corresponds to the time when transmission of one picture in the GOP from the demultiplexer 11 to the decoder 12 is started. Graphs 202 to 204 each represent the time required for transcoding one GOP of moving image data transcoded by the transcoder 1. In each of the graphs 202 to 204, each vertical line in the graph corresponds to the time when the encoder 15 finishes outputting one picture, that is, the time when transmission to the multiplexer 17 is finished.

For example, in FIG. 2A, the delay time Δt is the time t ₀ when transmission of the first I picture of the original moving image data to the decoder 12 is started, and the I picture is re-encoded as an I picture by the encoder 15. And a difference (t ₁ −t ₀ ) from the time t ₁ when the transmission to the multiplexer 17 is completed. In this case, since the I picture having a long time required for the decoding process and data transmission is encoded again as the I picture, the delay time Δt as a whole also becomes long.
On the other hand, in FIG. 2B, the delay time Δt is defined as the time t ₂ when transmission of the second P picture in the GOP of the original moving image data is started to the decoder 12 and the P picture as an I picture. It becomes a difference (t ₃ -t ₂ ) from time t ₃ when re-encoding and transmission to the multiplexer 17 is completed. In this case, since a P picture having a relatively short time required for decoding processing and data transmission from the demultiplexer 11 to the decoder 12 is re-encoded as an I picture, the time required until re-encoding is started is shown in the graph 202. It is shorter than the case shown in. Similarly, in FIG. 2C, the delay time Δt is re-encoded as a time t ₄ when transmission of the third P picture of the original moving image data is started to the decoder 12 and the P picture as an I picture. And a difference (t ₅ −t ₄ ) from the time t ₅ when the transmission to the multiplexer 17 is completed.

  In order to estimate the decoding start waiting period and re-encoding processing period of the encoding first picture, the time required for the decoding process, encoding process, and data transmission between each part, such as I picture and P picture, for each picture encoding type May be set in advance. Alternatively, the encoding start position determination unit 13 encodes the time required for the decoding process, the encoding process, and the data transmission between the respective encoding types by the first encoding method together with the encoding type. You may determine based on the encoding data amount of each picture. In this case, the relationship between the encoding type and the encoded data amount and the time required for the decoding process, the encoding process, and the data transmission is obtained in advance according to the processing capability of the transcoder 1. For example, a reference table indicating the relationship is stored in advance in a memory included in the encoding start position determination unit 13. Then, the encoding start position determination unit 13 refers to the reference table to determine the time required for the decoding process corresponding to the encoding type and the encoded data amount received from the demultiplexer 11, the encoding process, and the data transmission between the units. Can be identified. Further, the encoding start position determination unit 13 uses the time required for the decoding process of the pictures of each encoding type, the encoding process, and the data transmission between the parts for the encoding type, the encoded data amount of each picture, and the encoding thereof. It may be determined based on the determined quantization scale. Also in this case, the relationship between the encoding type, the encoded data amount, the quantization scale, and the time required for the decoding process, the encoding process, and the data transmission is obtained in advance according to the processing capacity of the transcoder 1. A reference table representing the relationship is stored in advance in a memory included in the encoding start position determination unit 13. The encoding start position determination unit 13 refers to the reference table, thereby performing decoding processing, encoding processing, and data transmission between the units corresponding to the encoding type, the encoded data amount, and the quantization scale received from the demultiplexer 11. The time required for

The encoding start position determination unit 13 changes the position of the encoded head picture one by one within the number included in the GOP, and calculates the delay time for each position. However, depending on the GOP structure of the original moving image data, the picture encoding order and the picture reproduction order may be different. When the encoding order and the reproduction order are different, depending on the number of discarded pictures, the decoding process of the picture by the decoder 12 may not be completed before the encoder 15 starts re-encoding for any picture. Therefore, the encoding start position determination unit 13 does not select the position of the encoded first picture corresponding to the discard number when the decoding of the picture is not completed before the start of re-encoding of any picture with respect to the predetermined discard number. The delay time is determined as follows. For example, the encoding start position determining unit 13 sets the delay time for the predetermined discard number to a value larger than the delay time when no picture is discarded.
The encoding start position determination unit 13 determines the number of discarded pictures corresponding to the position of the encoded first picture that minimizes the delay time. Then, the encoding start position determining unit 13 notifies the picture discarding unit 14 of the number of pictures discarded with the minimum delay time.

  The picture discarding unit 14 discards the discarded number of pictures notified from the encoding start position determining unit 13 for the first GOP in the decoded moving image data received from the decoder 12. Then, the picture discard unit 14 passes the pictures after the discarded picture to the encoder 15.

The encoder 15 re-encodes each picture received from the picture discarding unit 14 in accordance with a second encoding scheme that has higher encoding efficiency than the first encoding scheme. For example, when the second encoding method is H.264 MPEG-4 Advanced Video Coding (H.264 MPEG-4 AVC), the encoder 15 performs intra-picture prediction on a macroblock basis for an I picture. Do. Then, the encoder 15 performs orthogonal transform processing and quantization processing on the difference signal between the macroblock serving as the reference of the intra-picture prediction signal and the intra-picture prediction signal. On the other hand, for a P picture or a B picture, the encoder 15 creates a prediction signal by performing motion prediction and motion compensation between pictures in units of macroblocks, and applies a difference signal between the prediction signal and the macroblock. To perform orthogonal transform processing and quantization processing. Then, the encoder 15 performs variable-length coding on each quantized picture and motion vector, thereby generating encoded moving image data encoded according to the second method.
Further, the encoder 15 re-encodes the first picture among the pictures received from the picture discarding unit 14 as an I picture. The encoder 15 may re-encode the moving image data so as to have a GOP structure different from the GOP structure of the original encoded moving image data.
The encoder 15 outputs the encoded moving image data re-encoded according to the second encoding method to the multiplexer 17.

  The buffer 16 temporarily stores data such as audio signals and subtitles other than the encoded moving image data received from the demultiplexer 11. Then, the buffer 16 outputs the stored data to the multiplexer 17 after a certain period required for transcoding moving image data.

  The multiplexer 17 multiplexes the encoded moving image data received from the encoder 15 and the data such as audio signals and captions received from the buffer 16. And the multiplexer 17 divides | segments the video data produced | generated by the multiplexing into a packet unit according to the MPEG-2 TS format, for example, and outputs it for every packet.

FIG. 3 is an operation flowchart of transcoding processing executed by the transcoder 1. If each part of the transcoder 1 is a functional module realized by a computer program, the operation flow shown in FIG. 3 is controlled by a computer program that operates on a processor of the transcoder 1.
First, the demultiplexer 11 separates the multiplexed video signal input to the transcoder 1 into moving image data encoded according to the first encoding method and other data such as audio signals and captions. (Step S101). Then, the demultiplexer 11 passes the encoded moving image data to the decoder 12 in units of pictures. The demultiplexer 11 stores data other than the encoded moving image data in the buffer 16. Further, the demultiplexer 11 passes the encoding type of each picture included in the encoded moving image data, the data amount of each picture, and the quantization scale to the encoding start position determination unit 13.
Each time the decoder 12 receives the encoded picture from the demultiplexer 11, the decoder 12 decodes the encoded picture by a decoding method corresponding to the first encoding method (step S102). The decoder 12 delivers the decoded picture to the picture discarding unit 14 every time the picture is decoded.

  In addition, the encoding start position determination unit 13 estimates the delay time for each position while changing the position of the encoded first picture to be re-encoded for the first GOP of the encoded moving image data (step S103). ). Then, the encoding start position determination unit 13 determines the number of discarded pictures corresponding to the position of the encoded leading picture that minimizes the delay time (step S104). The encoding start position determining unit 13 notifies the picture discarding unit 14 of the obtained discard number.

The picture discarding unit 14 discards the number of pictures determined by the encoding start position determining unit 13 from the first picture among the decoded pictures sequentially received from the decoder 12 (step S105). Then, the picture discarding unit 14 passes the remaining pictures to the encoder 15. The encoder 15 uses the first picture of the remaining pictures received from the picture discarding unit 14 as an I picture, and encodes each picture according to the second encoding method to create re-encoded moving image data (step) S106). The encoder 15 passes the encoded picture to the multiplexer 17 every time encoding of one picture is completed. Then, the multiplexer 17 creates a video signal by multiplexing the re-encoded moving image data and other data such as an audio signal and subtitle, and outputs the multiplexed video signal (step S107). .
Note that the transcoder 1 may change the processing order of step S102 and steps S103 and S104. Alternatively, the transcoder 1 may execute the process of step S102 and the processes of steps S103 and S104 in parallel.

  As described above, the transcoder according to the first embodiment discards the first predetermined number of pictures including I pictures included in the input encoded video data, which require a long time for transcoding. . As a result, this transcoder can re-encode a P picture or a B picture with a short data transmission and decoding time as an I picture, and therefore can reduce a delay time due to transcoding.

  Note that the picture discarding unit may discard a predetermined number of pictures including an I picture in the first GOP included in the decoded moving image data. For example, the predetermined number is set to an arbitrary number within a range from one to one less than the total number of pictures included in the GOP. In this case, the encoding start position determination unit may be omitted.

Next, a transcoder according to the second embodiment will be described.
This transcoder determines the transmission timing of the transcoded reference picture based on the reception timing of the reference picture when the video signal is received, and executes the transmission timing adjustment by the multiplexer. And this transcoder adjusts the timing at which each part such as a decoder and encoder outputs a picture, so that it is not necessary to temporarily buffer data, thereby reducing the delay time by eliminating redundant waiting time. Shorten.

FIG. 4 is a schematic configuration diagram of the transcoder 2 according to the second embodiment. As shown in FIG. 2, the transcoder 2 includes a demultiplexer 11, a decoder 12, an encoder 15, a buffer 16, a multiplexer 17, and a picture timing detection unit 18.
The transcoder 2 according to the second embodiment differs from the transcoder 1 according to the first embodiment in that it includes a picture timing detection unit 18 instead of the encoding start position determination unit 13 and the picture discard unit 14. Therefore, in the following, differences from the transcoder 1 according to the first embodiment will be mainly described. Note that the same reference numerals as those of the corresponding components of the transcoder 1 shown in FIG. 1 are assigned to the components of the transcoder 2 shown in FIG.
Each of these units included in the transcoder 2 can be a separate circuit, for example. The transcoder 2 may be an integrated circuit in which circuits having functions of these units included in the transcoder 2 are integrated. Alternatively, each unit included in the transcoder 2 may be a functional module realized by a computer program executed on one or a plurality of processors included in the transcoder 2.

The demultiplexer 11 separates the multiplexed video signal input to the transcoder 1 in units of packets into moving image data encoded according to the first encoding method and other data such as audio signals and captions. To do. Then, the demultiplexer 11 passes the encoded moving image data to the decoder 12 in units of pictures. The demultiplexer 11 stores data other than the encoded moving image data in the buffer 16.
Further, the demultiplexer 11 notifies the picture timing detection unit 18 of header information of a packet including a picture of encoded moving image data from the input video signal packet. This packet is, for example, an MPEG-2 Packetized Elementary Stream (PES) packet. In addition, the demultiplexer 11 notifies the reception timing of each packet to the picture timing detection unit 18.

  The picture timing detection unit 18 detects, from the packet header information received from the demultiplexer 11, a packet including a reference picture, for example, the first GOP I picture. Then, the demultiplexer 11 extracts the identification information indicating that the reference picture is included in the packet as the reference picture identification information. This identification information can be, for example, a Presentation Time Stamp (PTS) used in MPEG-2 TS / PS.

  Furthermore, the picture timing detection unit 18 determines a transmission timing that is a timing at which the transcoder 2 transmits a packet including the transcoded reference picture. Therefore, the picture timing detection unit 18 determines a delay setting amount indicating a delay time from when a packet including a reference picture is input to the transcoder 2 until a packet including a transcoded reference picture is transmitted. . This delay setting amount is set in advance based on, for example, the amount of calculation required for each unit of the transcoder 2 to execute a series of processing on the reference picture and the processing capability of the transcoder 2. Alternatively, the delay setting amount may be set based on a history of a required time from when a packet including a reference picture is input to the demultiplexer 11 until transmission of the reference picture to the multiplexer 17 is completed. In this case, the transcoder 2 measures the required time each time a reference picture is input, and stores the required time in a memory (not shown) included in the transcoder 2. For example, the picture timing detection unit 18 uses the maximum value of the stored required time as the delay setting amount.

The picture timing determination unit 18 specifies the reception time of the packet including the reference picture from the reception time of each packet notified from the demultiplexer 11. Then, the picture timing determination unit 18 determines the transmission timing by adding the delay setting amount to the reception time of the packet including the reference picture.
The picture timing detection unit 18 notifies the multiplexer 17 of the transmission timing of the packet including the reference picture identification information and the reference picture.

The decoder 12 decodes each picture included in the moving image data encoded according to the first encoding method (for example, MPEG-2), and passes each decoded picture to the encoder 15. The encoder 15 re-encodes each decoded picture according to a second encoding scheme (for example, H.264 MPEG-4 AVC), and re-encodes each picture, that is, each transcoded picture. The picture is output to the multiplexer 17.
The demultiplexer 11, the decoder 12, and the encoder 15 transmit identification information indicating the reference picture extracted from the packet including the reference picture among the packets received by the demultiplexer 11 together with the reference picture. The identification information transmitted from the demultiplexer 11 to the multiplexer 17 via the decoder 12 and the encoder 15 is the same as the reference picture identification information extracted by the picture timing detection unit 18. Therefore, the multiplexer 17 can determine whether or not the reference picture has been received by checking whether or not the identification information received from the encoder 15 matches the reference picture identification information.

The multiplexer 17 multiplexes the encoded moving image data received from the encoder 15 and the data such as the audio signal and caption received from the buffer 16, and creates a packet including these data.
Further, the multiplexer 17 determines whether or not the identification information received together with the re-encoded picture from the encoder 15 matches the reference picture identification information received from the picture timing detection unit 18. If the two pieces of identification information match, the multiplexer 17 determines that the reference picture has been received. Then, the multiplexer 17 starts sending the packet storing the reference picture at the transmission timing received from the picture timing detection unit 18.
The multiplexer 17 determines the transmission timing of a packet including each picture after the reference picture with reference to a clock (for example, Program Clock Reference, PCR) corresponding to the reference picture. The multiplexer 17 determines the transmission timing of the packet including each picture by adding the difference between the clock corresponding to the reference picture and the clock corresponding to each picture to the transmission timing of the packet including the reference picture. .

FIG. 5 is a conceptual diagram of a delay time generated by the transcoder 2. In FIG. 5, a packet group 510 is a packet group including a video signal input to the transcoder 2. The packet group 520 is a packet group that includes moving image data transcoded by the transcoder 2 and is output by the transcoder 2. The reference pictures are included in the packets A to D of the packet group 510. In particular, it is assumed that the packet A includes a PTS corresponding to the reference picture, and the packet A is input to the transcoder 2 at 12:00:00. The delay setting amount is set to 500 milliseconds.
In this case, when the PTS sent together with the re-encoded picture from the encoder 15 matches the PTS sent from the picture timing determination unit 18, the multiplexer 17 determines that the picture is the reference picture. Then, the multiplexer 17 starts transmitting packets a to c including the reference picture in the packet group 520 in order from the packet a at a time obtained by adding 500 msec as a delay setting amount to 12:00:00.

  FIG. 6 is an operation flowchart of transcoding processing executed by the transcoder 2. When each part of the transcoder 2 is a functional module realized by a computer program, the operation flow shown in FIG. 6 is controlled by a computer program that operates on a processor included in the transcoder 2.

First, the demultiplexer 11 separates the multiplexed video signal input in units of packets into moving image data encoded according to the first encoding method and other data such as audio signals and subtitles ( Step S201). Then, the demultiplexer 11 passes the encoded moving image data to the decoder 12 in units of pictures. At that time, the demultiplexer 11 detects identification information for the reference picture from the header information of the packet, and passes the identification information to the decoder 12 together with the reference picture. The demultiplexer 11 stores data other than the encoded moving image data in the buffer 16. Further, the demultiplexer 11 notifies the picture timing detection unit 18 of header information of a packet including a picture of encoded moving image data.
The picture timing detection unit 18 determines the transmission timing by detecting the reference picture identification information from the header information of the packet and adding a predetermined delay time to the reception time of the packet including the reference picture (step S202). . Then, the picture timing detection unit 18 notifies the multiplexer 17 of the reference picture identification information and transmission timing.

  Each time the decoder 12 receives the encoded picture from the demultiplexer 11, the decoder 12 decodes each picture by a decoding method according to the first encoding method (step S203). Then, the decoder 12 passes each decoded picture to the encoder 15. At that time, the decoder 12 passes the identification information for the reference picture to the encoder 15 together with the decoded reference picture. The encoder 15 encodes each decoded picture according to the second encoding method (step S204). Then, the encoder 15 passes each re-encoded picture to the multiplexer 17. At that time, the encoder 15 passes the identification information for the reference picture to the multiplexer 17 together with the re-encoded reference picture.

  The multiplexer 17 multiplexes each picture of the re-encoded moving image data with other data such as an audio signal and subtitles to create a packet (step S205). Further, the multiplexer 17 determines whether or not identification information that matches the reference picture identification information has been received from the encoder 15 (step S206). If identification information that matches the reference picture identification information has not been received from the encoder 15 (step S206—No), the multiplexer 17 repeats the process of step S206. On the other hand, when the identification information matching the reference picture identification information is received from the encoder 15 (step S206—Yes), the multiplexer 17 determines that the picture received together with the identification information is the reference picture, thereby including the reference picture. A packet is specified (step S207).

  Next, the multiplexer 17 determines whether or not the current time has reached the transmission timing (step S208). When the current time is not the transmission timing (No at Step S208), the multiplexer 17 repeats the process at Step S208. On the other hand, when the current time is the transmission timing (step S208—Yes), the multiplexer 17 starts transmission from the packet including the re-encoded reference picture (step S209).

  As described above, the transcoder according to the second embodiment determines the transmission timing of the transcoded reference picture based on the reception timing of the reference picture when the video signal is received. The transcoder executes the transmission timing adjustment by a multiplexer. Therefore, this transcoder does not need to temporarily buffer data in order to adjust the timing at which each unit such as a decoder and encoder outputs a picture, so that redundant waiting time can be saved. Therefore, this transcoder can reduce the delay time due to transcoding.

  Next, a transcoder according to the third embodiment will be described. This transcoder is intended to further reduce the delay time by combining the function of the transcoder according to the first embodiment and the function of the transcoder according to the second embodiment.

  FIG. 7 is a schematic configuration diagram of the transcoder 3 according to the third embodiment. As shown in FIG. 7, the transcoder 3 includes a demultiplexer 11, a decoder 12, an encoding start position determination unit 13, a picture discard unit 14, an encoder 15, a buffer 16, a multiplexer 17, and a picture timing detection. Part 18. 7 are denoted by the same reference numerals as the corresponding components of the transcoder 1 shown in FIG. 1 and the transcoder 2 shown in FIG.

The transcoder 3 according to the third embodiment has both the parts of the transcoder 1 according to the first embodiment and the parts of the transcoder 2 according to the second embodiment. Each part of the encoder 3 has the same function as each corresponding part of the transcoder 1 and each corresponding part of the transcoder 2.
However, the demultiplexer 11 transmits not only the first I picture included in the original moving image data but also identification information indicating a packet including each picture to the decoder 12 together with each picture of the first GOP. The picture timing detection unit 18 uses the encoded first picture to be re-encoded determined by the encoding start position determination unit 13 as a reference picture. Then, the picture timing detection unit 18 determines reference picture identification information and transmission timing corresponding to the reference picture. The picture timing detection unit 18 can set the delay setting amount used for determining the transmission timing to be shorter than the delay setting amount used by the transcoder 2 according to the second embodiment. This is because the delay time due to the transcoding process is shortened by discarding the first predetermined number of pictures as described in the first embodiment.
Therefore, the transcoder according to the third embodiment can reduce the delay time due to the transcoding process, compared to the transcoder according to the first and second embodiments.
Also in the transcoder 3, when the picture discarding unit 14 discards a predetermined number of pictures including the first GOP I picture included in the original moving image data, the encoding start position determining unit 13 May be omitted. In this case, the picture timing detection unit 18 sets the next picture after the predetermined number of discarded pictures as a reference picture.

In each of the above embodiments, the first encoding method is not limited to MPEG-2, and may be another encoding method. For example, the first encoding method may be a Digital Video (DV) method. Also, the second encoding method is not limited to H.264 MPEG-4 AVC, and may be another encoding method. For example, the second encoding method may be MPEG-4.
Further, the first encoding method and the second encoding method may be the same. However, in this case, it is preferable that the encoder included in the transcoder converts the moving image data to the GOP configuration with higher compression efficiency than the GOP configuration of the original moving image data encoded by the first encoding method. . For example, when the GOP configuration of the original moving image data is a so-called IPPP configuration that does not include a B picture, the encoder converts the GOP configuration of the moving image data into, for example, an IBBP configuration that includes a B picture.

FIG. 8 is a schematic configuration diagram of a video retransmission system including the transcode of any of the above embodiments. As illustrated in FIG. 8, the video retransmission system 100 includes an antenna 101, a tuner device 102, a moving image transmission device 103, and a TS-IP conversion device 104.
The video re-transmission system 100 receives a video signal carried by broadcast radio waves via an antenna 101. The video signal is transmitted to a tuner device 102 connected to the antenna 101.
The tuner device 102 performs analog-digital conversion on the received video signal. The tuner device 102 demodulates the digitized video signal by a demodulation method (for example, Orthogonal Frequency Division Multiplexing (OFDM) demodulation method) according to the modulation method of the broadcast radio wave. The tuner device 102 performs error correction processing such as forward error correction on the demodulated video signal. Then, the tuner device 102 outputs a video signal that is packetized like an MPEG-2 TS packet obtained by being demodulated and subjected to error correction processing to the moving image transmission device 103.

The moving image transmission apparatus 103 transcodes the packetized video signal received from the tuner apparatus 102.
FIG. 9 is a schematic configuration diagram of the moving image transmission apparatus 103. As illustrated in FIG. 9, the moving image transmission apparatus 103 includes a reception unit 41, a real-time transcoder 42, an encryption unit 43, and a transmission unit 44.

  The receiving unit 41 has a communication interface for connecting the tuner device 102 and the moving image transmission device 103. The reception unit 41 receives the packetized video signal from the tuner device 102 and passes the video signal to the real-time transcoder 42.

  The real-time transcoder 42 converts the moving image data encoded by the first encoding method included in the video signal received via the receiving unit 41 into encoded moving image data according to the second encoding method. Convert. Then, the real-time transcoder 42 includes the moving image data encoded by the second encoding method again in a packet conforming to a moving image transmission standard such as an MPEG-2 TS packet. Therefore, the real-time transcoder 42 can be any of the transcoders of the above-described embodiments.

  The encryption unit 43 encrypts the video signal received from the real time transcoder 42. The encryption unit 43 can use, for example, a common key encryption method such as Advanced Encryption Standard (AES) or Camellia or a public key encryption method such as RSA encryption in order to encrypt the video signal.

  The transmission unit 44 has a communication interface that connects the TS-IP conversion device 104 and the moving image transmission device 103. Then, the transmission unit 44 outputs the video signal encrypted by the encryption unit 43 to the TS-IP conversion device 104.

The TS-IP conversion device 104 divides the video signal received from the moving image transmission device 103 into IP packets according to the Internet Protocol (IP). The TS-IP conversion device 104 transmits the IP packet to each video player 106 via a content delivery network (CDN) 105 that performs data communication according to the Internet protocol.
Note that the connection order of the moving image transmission apparatus 103 and the TS-IP conversion apparatus 104 may be switched. In this case, since the moving image transmission apparatus 103 receives the IP packetized video signal, the demultiplexer of the real-time transcoder 42 uses the IP packet packetized video according to the moving image transmission standard. Retrieve the signal. The transmission unit 44 converts the packetized video signal output from the encryption unit 43 according to the moving image transmission standard into an IP packet and outputs the IP packet.

  Since this video re-transmission system uses the transcoder of any of the above embodiments to transcode moving image data included in a video signal, the delay time generated by transcoding in the moving image transmission apparatus is reduced. it can. Therefore, this video re-transmission system can suppress the delay of the re-transmitted video signal with respect to the video signal directly transmitted by the broadcast radio wave.

  All examples and specific terms listed herein are intended for instructional purposes to help the reader understand the concepts contributed by the inventor to the present invention and the promotion of the technology. It should be construed that it is not limited to the construction of any example herein, such specific examples and conditions, with respect to showing the superiority and inferiority of the present invention. Although embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions and modifications can be made thereto without departing from the spirit and scope of the present invention.

The following supplementary notes are further disclosed regarding the embodiment described above and its modifications.
(Appendix 1)
A decoder that decodes each picture included in the first moving image data encoded according to the first encoding method;
A picture discarding unit for discarding a predetermined number of pictures including a first picture that is a reference for encoding other pictures in the first moving image data among the decoded pictures;
An encoder that re-encodes the remaining picture according to the second encoding method, with the first picture of the remaining pictures not discarded by the discarding unit as a picture that is a reference for encoding other pictures; ,
Transcoder with.
(Appendix 2)
While changing the position of the first picture, the time required from the start of transmission of the first picture to the decoder for the position of each first picture until the end of output of the encoded first picture by the encoder. Estimating a certain delay time, and calculating the number of pictures corresponding to the difference between the position of the first picture and the position of the first picture that minimizes the estimated delay time as the number of pictures to be discarded, The transcoder according to appendix 1, further comprising an encoding start position determining unit that notifies the picture discarding unit of the number of sheets.
(Appendix 3)
The encoding start position determining unit starts decoding until the first picture starts to be transmitted to the decoder after the first picture starts to be transmitted to the decoder according to a decoding order according to the first encoding method. Estimating a waiting period and a re-encoding process period from the start of transmission of the first picture to the decoder until the encoder finishes outputting the re-encoded leading picture, and the re-encoding process The transcoder according to appendix 2, wherein a difference between a period and the decoding start waiting period is the delay time.
(Appendix 4)
The encoding start position determination unit includes a data amount of each picture from the first picture encoded by the first encoding method to a first picture, a type of picture encoding method, and data transmission of the picture The calculation start waiting period and the re-encoding process period are calculated by referring to a table indicating a relationship between a time required for the decoding process by the decoder and a time required for the encoding process by the encoder, Transcoder.
(Appendix 5)
A video signal is received in packet units, moving image data encoded by the first encoding method is extracted from the video signal, and each picture included in the moving image data and other pictures of the pictures A demultiplexer that outputs first identification information corresponding to a reference picture that is a reference for encoding
A transmission timing representing a timing at which the reference picture is transmitted is determined by adding a predetermined delay time to the time when the first packet including the reference picture is received, and the reference packet is determined from the first packet. A picture timing determination unit for extracting second identification information for identifying a picture;
Decoding each encoded picture according to a first encoding scheme, outputting each of the decoded pictures, and receiving the first picture received from the demultiplexer in association with the decoded reference picture A decoder that outputs the identification information of
Re-encoding each decoded picture according to a second encoding scheme, outputting each of the re-encoded pictures, and receiving from the decoder in association with the re-encoded reference picture An encoder that outputs first identification information;
Packetizing each re-encoded picture and including a reference picture associated with the first identification information received from the encoder that matches the second identification information received from the picture timing determination unit A multiplexer that starts transmitting a packet at the transmission time;
Transcoder with.
(Appendix 6)
First identification for receiving a video signal in packet units, extracting moving image data encoded by the first encoding method from the video signal, and identifying each picture and each picture included in the moving image data A demultiplexer that outputs information respectively;
Each picture included in the first moving image data encoded according to the first encoding method is decoded, each of the decoded pictures is output, and each of the decoded pictures corresponding to each of the decoded pictures is output. A decoder for outputting the first identification information received from the multiplexer;
A picture discarding unit for discarding a predetermined number of pictures including a first picture that is a reference for encoding other pictures in the first moving image data among the decoded pictures;
The first picture of the remaining pictures not discarded by the discarding unit is used as a reference picture serving as a reference for encoding other pictures, and the remaining pictures are re-encoded according to the second encoding method, An encoder that outputs each of the re-encoded pictures and outputs the first identification information received from the decoder corresponding to each of the re-encoded pictures;
A transmission timing representing a timing at which the reference picture is transmitted is determined by adding a predetermined delay time to the time when the first packet including the reference picture is received, and the reference packet is determined from the first packet. A picture timing determination unit for extracting second identification information for identifying a picture;
When each of the re-encoded pictures received from the encoder is packetized and the second identification information received from the picture timing determination unit matches the first identification information, the first identification A multiplexer that starts transmitting a packet including a reference picture corresponding to information at the transmission time;
Transcoder with.
(Appendix 7)
A receiver for receiving video signals in units of packets;
A first moving image data encoded by the first encoding method from the video signal, and a multiplexer for separating other data;
A decoder for decoding each picture included in the first moving image data;
A picture discarding unit for discarding a predetermined number of pictures including a first picture that is a reference for encoding other pictures in the first moving image data among the decoded pictures;
An encoder that re-encodes the remaining picture according to the second encoding method, with the first picture of the remaining pictures not discarded by the discarding unit as a picture that is a reference for encoding other pictures; ,
A multiplexer that creates packets by multiplexing the other data and moving image data including each picture re-encoded according to the second encoding scheme;
An encryption unit for encrypting the packet;
A transmission unit for outputting the encrypted packet;
A moving image transmission apparatus.
(Appendix 8)
Decoding each picture included in the first moving image data encoded according to the first encoding method;
Among the decoded pictures, discard a predetermined number of pictures including a first picture that is a reference for encoding other pictures in the first moving image data,
Among the decoded pictures, the first picture of the remaining pictures that have not been discarded is used as a reference picture for coding other pictures, and the remaining pictures are re-executed according to the second coding scheme. Encoding,
A transcoding method.
(Appendix 9)
Decoding each picture included in the first moving image data encoded according to the first encoding method;
Among the decoded pictures, discard a predetermined number of pictures including a first picture that is a reference for encoding other pictures in the first moving image data,
Among the decoded pictures, the first picture of the remaining pictures that have not been discarded is used as a reference picture for coding other pictures, and the remaining pictures are re-executed according to the second coding scheme. Encoding,
A computer program for transcoding that causes a computer to execute this.

1, 2, 3 Transcoder 11 Demultiplexer 12 Decoder 13 Encoding start position determining unit 14 Picture discarding unit 15 Encoder 16 Buffer 17 Multiplexer 18 Picture timing detecting unit 100 Video retransmission system 101 Antenna 102 Tuner device 103 Video transmission device 104 TS -IP converter 41 Receiver 42 Real-time transcoder 43 Encryptor 44 Transmitter

Claims (7)

A decoder that decodes each picture included in the first moving image data encoded according to the first encoding method;
A picture discarding unit for discarding a predetermined number of pictures including a first picture that is a reference for encoding other pictures in the first moving image data among the decoded pictures;
An encoder that re-encodes the remaining picture according to the second encoding method, with the first picture of the remaining pictures not discarded by the discarding unit as a picture that is a reference for encoding other pictures; ,
Transcoder with.   While changing the position of the head picture, the time required from the start of transmission of the head picture to the decoder for the position of each head picture until the encoder finishes outputting the encoded head picture. Estimating a certain delay time, calculating the number of pictures corresponding to the difference between the position of the first picture and the position of the first picture that minimizes the estimated delay time as the number of pictures to be discarded, The transcoder according to claim 1, further comprising an encoding start position determination unit that notifies the picture discarding unit of the number of sheets.   The encoding start position determining unit starts decoding until the first picture starts to be transmitted to the decoder after the first picture starts to be transmitted to the decoder according to a decoding order according to the first encoding method. Estimating a waiting period and a re-encoding process period from the start of transmission of the first picture to the decoder until the encoder finishes outputting the re-encoded leading picture, and the re-encoding process The transcoder according to claim 2, wherein a difference between a period and the decoding start waiting period is the delay time.   The encoding start position determination unit includes a data amount of each picture from the first picture encoded by the first encoding method to a first picture, a type of picture encoding method, and data transmission of the picture The decoding start waiting period and the re-encoding process period are calculated by referring to a table indicating a relationship between a time required for the decoding process by the decoder and a time required for the encoding process by the encoder. The described transcoder. A receiver for receiving video signals in units of packets;
A first moving image data encoded by the first encoding method from the video signal, and a multiplexer for separating other data;
A decoder for decoding each picture included in the first moving image data;
A picture discarding unit for discarding a predetermined number of pictures including a first picture that is a reference for encoding other pictures in the first moving image data among the decoded pictures;
An encoder that re-encodes the remaining picture according to the second encoding method, with the first picture of the remaining pictures not discarded by the discarding unit as a picture that is a reference for encoding other pictures; ,
A multiplexer that creates packets by multiplexing the other data and moving image data including each picture re-encoded according to the second encoding scheme;
An encryption unit for encrypting the packet;
A transmission unit for outputting the encrypted packet;
A moving image transmission apparatus. Decoding each picture included in the first moving image data encoded according to the first encoding method;
Among the decoded pictures, discard a predetermined number of pictures including a first picture that is a reference for encoding other pictures in the first moving image data,
Among the decoded pictures, the first picture of the remaining pictures that have not been discarded is used as a reference picture for coding other pictures, and the remaining pictures are re-executed according to the second coding scheme. Encoding,
A transcoding method. Decoding each picture included in the first moving image data encoded according to the first encoding method;
Among the decoded pictures, discard a predetermined number of pictures including a first picture that is a reference for encoding other pictures in the first moving image data,
Among the decoded pictures, the first picture of the remaining pictures that have not been discarded is used as a reference picture for coding other pictures, and the remaining pictures are re-executed according to the second coding scheme. Encoding,
A computer program for transcoding that causes a computer to execute this.

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