JP2007227993A - Transcoder and transcoding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transcoder for decoding moving picture encoded data and reencoding it with different encoding parameters in which the need for frame memory is eliminated by eliminating the need for reordering which is conventionally required in the reencoding process, and to provide a transcoding method. <P>SOLUTION: The transcoder comprises a control section 1 for controlling an encoding section, a storage section and a decoding section, a section 3 for storing moving picture encoded data, a section 4 for decoding moving picture encoded data, and a section 2 for reencoding the decoded image wherein the moving picture encoded data is read out twice, images reencoded as I picture and P picture are decoded in the first time read out, and an image reencoded as B picture is decoded in the second time read out. An image line is formed in the reordering order for encoding, i.e. the order of images to be encoded, and then it is reencoded. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a transcoder and a transcoding method in which moving image encoded data subjected to high efficiency encoding is decoded and then encoded again.

In recent years, HDD recorders that record moving images have become widespread. These are mainly intended for recording television broadcasts, and in the case of analog broadcasts, high-efficiency encoding is performed by the MPEG method and recorded on the HDD. In the case of digital broadcasting, moving image encoded data that has been encoded with high efficiency according to the MPEG system is input, so that the encoded moving image data is recorded without being encoded with high efficiency, or once decoded, the resolution and bit Record high-efficiency encoded data at different rates. However, when recording a digital broadcast, even if it is not highly efficient encoding, it does not record the moving image encoded data itself, but usually the encoded data after channel selection or the encoding that is uniquely encrypted Record the data.
Some HDD recorders include a DVD recorder, and broadcast waves can be directly recorded on a DVD, or moving image data once recorded on an HDD can be recorded again on a DVD.

  When re-recording from the HDD to the DVD, the moving image encoded data may be temporarily decoded and re-encoded by changing the resolution and bit rate due to limitations on the encoding format, recording capacity and recording speed that can be recorded on the DVD. In particular, a DVD has a smaller recording capacity than an HDD, and therefore recording is generally performed at a low bit rate.

As an apparatus for re-encoding at a low bit rate (hereinafter, re-encoding is referred to as transcoding, and the re-encoding apparatus is referred to as a transcoder), for example, Japanese Patent Application Laid-Open No. 2004-151867 discloses the technique. In the technique described in this document, the types of encoded images include intra-frame encoded images (hereinafter referred to as I pictures), inter-frame forward prediction encoded images (hereinafter referred to as P pictures), bidirectional prediction. There are encoded pictures (hereinafter referred to as B pictures), and among these, I pictures and P pictures are used with the feature that the code quantity of I pictures is the largest, followed by P pictures and B pictures in that order. Is re-encoded to reduce the number of. For example, when the picture group is encoded as (IBBPBBIBBBPBBP), the picture group is once decoded to generate a decoded image, and the decoded image sequence is re-encoded as (IBBBBBBPBBBBBBP).
JP 2005-123829 A

However, the transcoding method as found in Patent Document 1 has a problem that a large number of frame memories are required for re-encoding.
For example, FIG. 12 shows an example in the case of re-encoding as a picture group (IBBBBBBPBBBBBP). As shown in FIG. 12A, images to be encoded are input in the order of I1, B2, B3, B4, B5, B6, P7, B8, B9, B10, B11, B12, and P13 from the left. Here, I1 is encoded as an I picture, P7 and P13 are encoded as P pictures, and the other images are encoded as B pictures. Since the B picture is predictively encoded from both directions, it is necessary to encode the preceding and succeeding I or P pictures and generate a local decoded image prior to encoding the B picture. For example, since B2 to B6 are predicted from local decoded images of I1 and P7, I1 and P7 are encoded before encoding of B2 to B6. Therefore, the encoding order is I1, P7, B2, B3, B4, B5, B6, P13, B8, B9, B10, B11, B12. This replacement of the input image in the encoding order is called reordering. In the conventional transcoding method, B2 to B6 and B8 to B12 must be temporarily recorded in the frame memory for reordering and held until the encoding of P7 and P13 is completed. That is, in the example of FIG. 12, a frame memory for 5 frames is required to hold B2 to B6 or B8 to B12.
In view of such circumstances, an object of the present invention is to provide a transcoder and a transcoding method that can be re-encoded with a small amount of memory.

  The transcoder of the present invention that solves the above-described problems decodes moving image encoded data that has been encoded with high efficiency, encodes the decoded image into an intra-frame, forward inter-frame predictive encoding, and bidirectional inter-frame. A transcoder that performs re-encoding by combining encoding types of predictive encoding, the storage unit storing the moving image encoded data, the decoding unit decoding the moving image encoded data, and the decoded image And a storage unit, the decoding unit, and a control unit for controlling the encoding unit, and the encoding type to be re-encoded is intra-frame encoding and forward inter-frame prediction code. A picture group is an image group in which two images to be encoded and an image type that is re-encoded between the images are bidirectional inter-frame predictive encoding, and the control unit encodes the image to be re-encoded Setting, and controlling to read out the moving image encoded data of the picture group or a part thereof from the storage unit as the first moving image encoded data and the second moving image encoded data, The moving image encoded data includes moving image encoded data capable of decoding an undecoded image among images whose encoding types to be re-encoded are intra-frame encoding and forward inter-frame prediction encoding. The moving image encoded data of 2 includes moving image encoded data in which an image whose recoding type is bidirectional inter-frame prediction encoding can be decoded, and the decoding unit includes the first moving image code. Decoding at least re-encoding from the second moving image encoded data by decoding an image having at least re-encoding encoding type intra-frame encoding and forward inter-frame predictive encoding from the encoded data The decoder decodes a bidirectional inter-frame predictive encoded image, outputs the decoded image in the re-encoded encoding order, and the encoding unit re-encodes the decoded image with a set encoding type. And

  In addition, the transcoding method of the present invention that solves the above-described problem is to decode high-efficiency encoded moving image encoded data, encode the decoded image into an intra-frame, forward inter-frame predictive encoding, bidirectional The transcoding method for re-encoding by combining the encoding types of the inter-frame predictive encoding, wherein the encoding types to be re-encoded are intra-frame encoding and forward inter-frame predictive encoding An image group in which an encoding type set between images is bidirectional inter-frame predictive encoding is a picture group, and the intra-frame encoding and forward inter-frame predictive code in the picture group are set as a picture group. Decoded images that are decoded and then decoded in the picture group, and then decoded in the bi-directional interframe predictive coding within the picture group. Generated, wherein the re-encoding the decoded image.

  In the transcoder and transcoding method according to the present invention, an image to be subjected to intra-frame coding and forward inter-frame predictive coding is first decoded and re-encoded in the order after re-ordering necessary for re-encoding. An image sequence is generated, that is, moving image encoded data is read twice, an image that is subjected to intra-frame encoding and forward inter-frame prediction encoding is decoded at the first reading, and a bidirectional frame is read at the second reading. An image to be subjected to inter-prediction encoding is decoded, so that the frame memory used for reordering in re-encoding is not necessary. In addition, since reordering is unnecessary, there is an effect that encoding control of re-encoding becomes easy. Furthermore, there is no restriction on the type of re-encoding, and there is also an effect that encoding at a low bit rate is facilitated by control such as greatly increasing the number of B pictures.

  The best mode for carrying out the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to these embodiments, and can be implemented in various modes without departing from the spirit of the present invention.

The present embodiment proposes a transcoder and transcoding method that can transcode with a small number of frame memories by decoding I picture and P picture in moving picture encoded data first.
FIG. 1 illustrates functional blocks of the transcoder according to this embodiment. The transcoder shown in FIG. 1 includes a control unit 1 that controls an encoding unit 2, a storage unit 3, and a decoding unit 4, a storage unit 3 that stores moving image encoded data, and a decoding unit that decodes moving image encoded data. 4 and an encoding unit 2 that re-encodes the decoded image.

In the following, a broadcast input from the outside is encoded by the encoding unit 2, the moving image encoded data shown in FIG. 2 is generated and recorded in the storage unit 3, and the moving image encoded data is decoded by the decoding unit 4. An example of transcoding with the re-encoding type shown in FIG.
The moving image encoded data shown in FIG. 2 is recorded in the storage unit 3, the moving image encoded data is decoded by the decoding unit 4, and transcoded by the re-encoding type shown in FIG. 3 by the encoding unit 2. An example will be described. In the following description, the encoding type of moving image encoded data is distinguished using lowercase i, p, b, and the encoding type to be recoded is distinguished using uppercase I, P, B.

  FIG. 2A shows an image sequence and encoding type before moving image encoded data is generated, i1, i13 are images input in the order of i1, b2, and b3, i4 is an i picture, and p4, p7. , P10 are encoded as p pictures, and the others are encoded as b pictures. Encoding is performed in the order shown in FIG. In other words, since the b picture uses the immediately following i or p picture as a reference image for prediction, the i or p picture is encoded first.

  The encoded moving image data shown in FIG. 2B is recorded in the storage unit 3 and transcoded to the encoding type shown in FIG. Here, a set of two images to be re-encoded as an I picture or a P picture and an image surrounded by them and encoded as a B picture is called a picture group. FIG. 3B shows a picture group in this example. I1 to P7 and P7 to I13 each constitute a picture group.

  The moving image encoded data encoded in the order shown in FIG. 2 is recorded in the storage unit 3, and the moving image encoded data of the picture group is output to the decoding unit 4 under the control of the control unit 1. . FIG. 4 shows encoded data input from the storage unit 3 to the decoding unit 4 and a decoded image sequence output from the decoding unit 4 and input to the encoding unit 2.

  FIG. 4A shows moving image encoded data recorded in the storage unit 3, and the moving image encoded data is input to the decoding unit 4 twice for each picture group. FIG. 4B shows the first moving image encoded data, and the decoding unit 4 re-encodes the encoded data as an I picture or P picture from the encoded data, that is, i1, p7 for the first picture group. Is output to the encoding unit 2. In order to decode i1 and p7, it is only necessary to have the moving image encoded data of i1, p4 and p7, and the moving image encoded data of b2 and b3 between them need not be read. Although images other than i1 and p7 are also decoded, they are not output to the encoding unit 2. FIG. 4C shows the second moving image encoded data. The decoding unit 4 decodes an image to be re-encoded as a B picture from the moving image encoded data, and encodes the decoded image sequence into the encoding unit 2. Output to. For the first picture group, b2, b3, p4, b5, b6 are decoded and output. Here, b2, b3, p4, b5, and b6 moving image encoded data only need to be present, and p7 in between is already decoded when the first moving image encoded data is read, so that the second moving image encoded data is present. Then there is no need to read. Thus, the decoded image sequence is input to the decoding unit 4 in the encoding order after reordering. Similarly, for the next picture group, i13 is decoded from the first moving image encoded data, output to the encoding unit 2 and held in the decoding unit 4, and b8, b9, p10, b11, and b12 are decoded and the decoded image sequence is input to the decoding unit 2. The I and P pictures constituting the second picture group are p7 and i13. However, since p7 overlaps with the first picture group and has already been input to the encoding unit 2, the second picture group Decryption is not performed in group processing.

  Under the control of the control unit 1, the encoding unit 2 encodes the input image sequence with the encoding type shown in FIG. 3A without reordering. That is, encoding is performed in the order of I1, P7, B2, and B3, and the moving image encoded data is output to the storage unit 3. The encoding unit 2 includes a frame memory for holding a locally decoded image, but does not need to include a frame memory for reordering that is conventionally required. The storage unit 3 is composed of, for example, an HDD, a recordable DVD, or both. When both are configured, the moving image encoded data recorded on the HDD can be re-encoded at a low bit rate and recorded on a recordable DVD. In this embodiment, the encoding unit 2 performs both encoding of the broadcast wave input and re-encoding of the encoded moving image encoded data. However, the encoding circuit and the re-encoding circuit are And encoding and re-encoding may be performed by each circuit.

  Next, as an example of other moving image encoded data, the moving image encoded data shown in FIG. 5 is recorded in the storage unit 3, and the moving image encoded data is decoded by the decoding unit 4, An example of transcoding with the re-encoding type shown in FIG. 3 in the encoding unit 2 will be described. The moving image encoded data in FIGS. 2 and 5 differ in the encoding type of the 13th image. That is, although encoded as an i picture in FIG. 2, it is encoded as a p picture in FIG. FIG. 6 shows the encoded data input from the storage unit 3 to the decoding unit 4 and the decoded image sequence output from the decoding unit 4 and input to the encoding unit 2 for the moving image encoded data in FIG.

  4 and 6 differ in the readout of moving image encoded data for generating the 13th decoded image. That is, in the example of FIG. 4, since the 13th image is encoded as an i picture, only the encoded data of the picture can be read and i13 can be decoded. However, in the example of FIG. Since it is encoded, it is necessary to read and decode the encoded data of p10 used for prediction as shown in FIG. 6B. In addition, decoding of p13 requires moving image encoded data of p10 and p13, and moving image encoded data of b8 and b9 encoded between them need not be read. The other processes are the same in FIGS. 4 and 6, and the decoded image sequence shown in FIG. 6D is output from the decoding unit 4 to the encoding unit 2.

  FIG. 7 illustrates a processing flow in the transcoder and transcoding method according to this embodiment. FIG. 7 shows the flow of encoded image data read from the storage unit 3 according to the encoding type set by the control unit 1 shown in FIG. 1, and the decoding and decoded image output processing in the decoding unit 4. is there.

In FIG. 7, the encoding type which the control part 1 re-encodes first is set (step S1). That is, a picture group is set, and it is set whether to encode an I picture or a P picture at the beginning and the rear end of the picture group. There is no limitation on the setting of the picture group. For example, as shown in FIG. 3, the i picture of the moving image encoded data is re-encoded as an I picture, and a part of the p picture is re-encoded as a B picture. Alternatively, all p pictures are re-encoded as B pictures. Or the setting which arrange | positions an I picture, a P picture, and a B picture at fixed intervals can be considered.
Next, it is determined whether or not the leading image of the picture group has been decoded (step S2). The leading image of the picture group is the same as the trailing image of the immediately preceding picture group. Therefore, in the case of the first picture group to be transcoded, the first picture has not been decoded, but from the second picture group, it has been decoded by the process of the previous picture group. If the first picture of the picture group has not been decoded, moving image encoded data that can be decoded by the first picture and the rear picture of the picture group is read (step S3), and the first picture and the rear picture are decoded and output (step S3). Step S4). The procedure for determining the moving image encoded data read in step S3 will be described later. If the leading image has been decoded in step S2, moving image encoded data that can be decoded by the trailing image of the picture group is read (step S5), and the trailing image is decoded and output (step S6). The procedure for determining the moving image encoded data to be read in step S5 will also be described later. Next, the encoded video data that can be decoded by the picture group other than the first picture and the rear picture, that is, the picture to be re-encoded as a B picture is read (step S7), and the image to be re-encoded as a B picture is decoded. Output (step S8). The procedure for determining the moving image encoded data to be read in step S8 will also be described later.

  In step S8, among the images encoded as i pictures or p pictures in the picture group, the last decoded image in the picture group and the image in the next picture group are held. For example, in the example of re-encoding shown in FIG. 3, p7 is held for the first picture group. This is because a decoded image of p7 is necessary for decoding b8, b9, and p10 at the time of decoding the moving image encoded data of the next picture group, but the procedure for decoding p7 again is omitted. Another example of re-encoding is shown in FIG. FIG. 8 is a diagram in which the number of images constituting the picture group is changed. For the first picture group, the decoded image of p4 encoded as the p picture and the decoded image of p7 of the next picture group are held. This is also because the decoded images of p4 and p7 are necessary for decoding of b6 when decoding the moving picture encoded data of the next picture group, so that the procedure of decoding p4 and p7 again is omitted.

  Then, it is determined whether or not the transcoding is completed (step S9). If not, the steps S1 to S8 are repeated. In the case of termination, the transcoding process is terminated.

  FIG. 9 shows a procedure for reading moving image encoded data in which the first image and the rear image of the picture group shown in step S3 can be decoded. In the flow of FIG. 9, it is first determined whether or not the first picture of a picture group to be re-encoded is encoded as an i picture (step S11). In the case of an i picture, moving picture encoded data is read from the i picture. (Step S12). If it is not an i picture, the first picture of the picture group has been predictively encoded from the previous picture, so an i picture preceding the picture group is searched and read from the searched i picture (step S13). Then, even the moving image encoded data corresponding to the rear end image of the picture group is read (step S14). With the above operation, moving image encoded data that can decode the head and the rear end of the picture group is read.

  Next, FIG. 10 shows a procedure for reading moving image encoded data in which the rear end image of the picture group shown in step S5 can be decoded. In the flow of FIG. 10, it is first determined whether or not the rear end image of a picture group to be re-encoded is encoded as an i picture (step S21). In the case of an i picture, only the moving image encoded data of the i picture is determined. Therefore, the moving image encoded data is read from the i picture (step S22). If it is not an i picture, it is determined whether there is an i picture in the picture group to be re-encoded (step S23). If there is an i picture, the rear end image of the picture group is predicted from the i picture as a starting point. Therefore, moving image encoded data is read from the i picture (step S24). If there is no i picture, it is next determined whether or not there is a p picture in the picture group (step S25). If there is a p picture, moving picture encoded data is read from the p picture (step S26). The reference picture is necessary for decoding the p picture, but it has been decoded in the process of generating the image sequence of the previous picture group, and is held in the decoding unit (104). If there is no i picture or p picture in the picture group, the picture group is read from the moving picture encoded data corresponding to the rear end picture of the picture group (step S27). In this case, the rear end image is encoded as a b picture, and a reference image used for prediction is necessary here, but the reference image has been decoded in the decoding process for generating the image sequence of the immediately preceding picture group, It is held in the decoding unit 4. Next, the reading operation is continued until the reading of the moving image encoded data corresponding to the rear end image of the picture group is completed (step S28). With the above flow, moving image encoded data that can decode the rear end of the picture group is read out.

  Next, FIG. 11 shows a procedure for reading moving image encoded data in which a re-encoding encoding type B picture can be decoded shown in step S7. In the flow of FIG. 11, first, moving image encoded data corresponding to an image encoded as an i picture or a p picture next to the first image of a picture group to be re-encoded is set as a read start position (step S31). This is because i-pictures or p-pictures were previously encoded in the moving image encoded data for reordering. In the example of FIGS. 2 and 3, the first image of the picture group is i1, and the next image encoded as an i picture or p picture is p4. That is, the moving image encoded data is read in the order of p4, b2, and b3. These decodings require i1 as a reference image, but have already been decoded by reading the first moving image encoded data, and i1 moving image encoded data is not read by the second reading. Next, it is determined whether the rear end image of the picture group is encoded as an i picture or a p picture (step S32). If it is encoded as an i-picture or p-picture, the moving image encoded data up to immediately before the next i-picture or p-picture of the rear end image is read (step S33). In the example of FIGS. 2 and 3, the rear end image of the picture group is p7, and the next i picture or p picture is p10. That is, up to b6 which is the moving image code immediately before p10 is read. If the rear end image of the picture group is not encoded as an i picture or a p picture, the moving image encoded data up to immediately before the rear end image is read (step S34). In this case, the rear end image is encoded as a b picture, and is encoded after an i picture or a p picture used for prediction in reordering. That is, when the encoded moving image data of the rear end image is read, the encoded moving image data that can decode all the pictures in the picture group is read out.

  The flow described with reference to FIGS. 7 to 11 is a procedure for reading moving image encoded data without waste. In order to make the control easier, moving image encoded data that can always be decoded by all picture groups regardless of the encoding type being encoded is read, and only necessary decoded images are read from the decoding unit 4 to the encoding unit 2. May be output.

It is a figure which shows an example of the functional block of the transcoder which concerns on embodiment of this invention. It is a figure which shows the example of the image sequence currently encoded as moving image encoded data. It is a figure which shows the example of the encoding type and picture group of re-encoding. It is a figure which shows the example of reading of the moving image encoded data in embodiment of this invention. It is a figure which shows an example of the other image sequence encoded as moving image encoded data. It is a figure which shows the other example of reading of the moving image encoded data in embodiment of this invention. It is a flowchart which shows the flow of the read-out and decoding process of moving image coding data in embodiment of this invention. It is a figure which shows the other example of the encoding type and picture group of re-encoding. It is a flowchart which determines the moving image coding data read by step S3 in FIG. It is a flowchart which determines the moving image coding data read by step S5 in FIG. It is a flowchart which determines the moving image coding data read by step S7 of FIG. It is a figure which shows the example of an encoding type and an encoding order.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Control part, 2 ... Encoding part, 3 ... Accumulation part, 4 ... Decoding part.

Claims (2)

Decodes high-efficiency encoded video encoded data, and re-encodes the decoded image using a combination of intra-frame encoding, forward inter-frame predictive encoding, and bidirectional inter-frame predictive encoding. A transcoder that
A storage unit that stores the encoded video data, a decoding unit that decodes the encoded video data, an encoding unit that re-encodes the decoded image, the storage unit, the decoding unit, and the code A control unit for controlling the control unit,
Two images whose encoding type to be recoded is intraframe coding and forward interframe predictive coding, and the coding type to be recoded between the images is bidirectional interframe predictive coding Let the image group be a picture group,
The control unit sets an encoding type of an image to be re-encoded, and the moving image encoded data of the picture group or a part thereof is transferred from the storage unit to the first moving image encoded data and the second moving image code. The first moving image encoded data is controlled to be read out twice as encoded data, and the first moving image encoded data is an undecoded image among the images whose encoding types to be re-encoded are intra-frame encoding and forward inter-frame predictive encoding. Video encoded data including video encoded data capable of decoding an image, wherein the second video encoded data is capable of decoding an image whose encoding type is bidirectional inter-frame predictive encoding. The decoding unit decodes at least the image whose re-encoding type is intra-frame encoding and forward inter-frame predictive encoding from the first moving image encoded data, Video From the encoded data, at least a re-encoding encoding type of inter-frame predictive encoding image is decoded, decoded images are output in the re-encoding encoding order, and the encoding unit sets the decoded image Re-encoding with encoding type,
Transcoder characterized by. Decodes high-efficiency encoded video encoded data, and re-encodes the decoded image using a combination of intra-frame encoding, forward inter-frame predictive encoding, and bidirectional inter-frame predictive encoding. A transcoding method,
Two images in which the encoding type to be re-encoded is intra-frame encoding and forward inter-frame predictive encoding, and an image group in which the encoding type set between the images is bidirectional inter-frame predictive encoding Is a picture group,
In the picture group, two images whose decoding types are intraframe encoding and forward interframe predictive encoding are decoded, and then an image for bidirectional interframe predictive encoding in the picture group is decoded. Decoding, generating a decoded image in the encoding order of re-encoding, and re-encoding the decoded image;
A transcoding method characterized by the above.

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