Abstract:
An editing device for connecting first and second streams containing variable length coded parameters, includes a decision unit operable to compare an encoded first parameter contained in the first stream with an encoded second parameter contained in the second stream, and decide whether at least one of the first parameter and the second parameter is to be changed, and a replacing unit operable to replace at least one of the first and second parameters with the other code word of the same length as the code words assigned to the first and second parameters, when the decision unit decides that at least one of the parameters is to be changed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a divisional application of U.S. patent application Ser. No. 12/302,940, filed on Dec. 1, 2008, which is a National Stage Application of International Application No. PCT/JP2007/061502 filed May 31, 2007, the disclosure of which, including the specification, drawings, and claims, is incorporate herein by reference in its entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to an editing device for editing a stream. 
     2. Related Art 
     Variable length coding (VLC) is a fundamental technology used in encoding source data, and compresses the data by allocating code words of different lengths according to the likelihood of a particular data source symbol. Using coding rules such as shown in  FIG. 24 , for example, values (codeNum) greater than 0 are converted to variable length code words of 1, 3, 5, . . . bits. Note that the bit string part denoted x n , x n-1 , . . . x 0  is the part of the bit string that varies according to the data value (codeNum). For example, a value (codeNum) of 1 or 2 is encoded to a 3 bit code word, and values from 7 to 14 are converted to a 7 bit code word. The length of the code words after encoding thus varies according to the data value (codeNum) being encoded by VLC. 
     VLC is used in encoding standards for motion picture represented by MPEG. More particularly, Target to which VLC is applied is classified into syntax of video encoded data such as the DCT coefficient and motion vectors of image pixel blocks, and syntax for the header. As the coding tools used in image compression technology have become more versatile and complex, the syntax types used in the header have also increased, and VLC is increasingly used in the header syntax in order to reduce the code size. 
     The H.264/AVC standard (ISO/IEC 14496-10) (see ISO/IEC 14496-10, Advanced video coding for generic audio/visual services) also uses VLC for various syntax included in the sequence parameter set (SPS), the picture parameter set (PPS) and the Slice header. 
       FIG. 21  to  FIG. 23  outline the syntax of the SPS, PPS, and slice header. “Descriptor” of ue(v) or se(v) in these figures denotes a VLC syntax, where ue(v) indicates coding values (codeNum) greater than 0 to VLC words of 1, 3, 5, . . . bits as shown in  FIG. 24 , and se(v) indicates coding in VLC as shown in  FIG. 24  after first converting signed values to a codeNum as shown in  FIG. 25 . 
     Configuration of the H.264 byte stream is described next with reference to  FIG. 26  to  FIG. 29 . The image coding data is stored in the slice data (slice data) shown in  FIG. 28 . A slice is one division of the picture divided into n parts (n≧1), and is a set of macroblocks. The slice data is coded with the slice header in a slice layer (slice_layer_without_partitioning_rbsp) shown in  FIG. 27 . The SPS, PPS, and slice layer are packetized as a NAL unit (nal_unit) shown in  FIG. 26 . When NAL units containing the SPS, PPS, and slice layer are multiplexed into a single stream, the NAL units are packetized into byte stream NAL units (byte_stream_nal_unit, “BNU” below) connected in a single byte stream. 
     The process to connect plural H.264 byte streams by the video editing device is described next with reference to  FIG. 30 . More specifically,  FIG. 30  shows the process of connecting substream a ( 153 ) in stream A ( 150 ) and substream b ( 163 ) in stream B ( 160 ) to generate byte stream C ( 170 ). 
     Stream A ( 150 ) includes the byte stream NAL unit (SPS-BNU)  151  of the SPS  110 , the byte stream NAL unit (PPS-BNU)  152  of the PPS  111 , and the substream a ( 153 ) of the scene to be connected to substream b ( 163 ). Likewise, stream B ( 160 ) includes the SPS-BNU  161 , the PPS-BNU  162 , and the substream b ( 163 ) of the scene to be connected to substream a ( 153 ). Each substream a ( 153 ) and substream b ( 163 ) contains one or more sets including a byte/NAL header (for example,  101 ), slice header (for example,  120 ), and slice data (for example,  121 ). 
     In this example it is assumed that stream A ( 150 ) and stream B ( 160 ) contain IDR (Instantaneous Decoding Refresh) pictures, and the code size of all IDR pictures is the same in stream A ( 150 ) and stream B ( 160 ). The SPS and PPS are also assumed to be at the beginning of the byte stream. 
     The H.264 standard uses the idr_pic_id as the IDR picture identifier (ID). As shown in  FIG. 23 , the idr_pic_id is found in the slice header and contains a VLC value. To assure stream compatibility, the H.264 standard requires that the idr_pic_id of adjacent IDR pictures are set to different values. 
     The process of connecting substream a ( 153 ) and substream b ( 163 ) based on the foregoing assumptions generates a new byte stream C ( 170 ) by connecting substream a ( 153 ) and substream b ( 163 ) while rewriting the idr_pic_id contained in all of the slice headers in the pictures where the streams are connected to different values in adjacent pictures in order to assure readability and compatibility. More specifically, each of the adjacent pictures in stream A ( 150 ) and stream B ( 160 ) before the streams are connected is assigned a different idr_pic_id, and it is also necessary to ensure that the pictures that are adjacent where the streams are connected are also assigned a different idr_pic_id after the streams are connected. 
     SUMMARY 
     In order to assure the idr_pic_id is different in each picture made newly adjacent where two streams are connected (also referred to below as the “seam”), the value of the idr_pic_id must be overwritten in the pictures that are adjacent at the seam immediately after the streams are connected. 
     The value of the idr_pic_id is obtained by VLC. When the value of the idr_pic_id in one IDR picture is overwritten so that the idr_pic_id differs from the idr_pic_id in the adjacent IDR picture, the length of the idr_pic_id code word may be different before and after the values are changed. This may make it necessary to modify the data following the idr_pic_id, and the process becomes increasingly complicated. 
     As shown in  FIG. 31 , for example, in order to assign a different idr_pic_id to the adjacent IDR pictures where streams recorded to a recording medium are connected, it may be necessary to change the code word 011 of the idr_pic_id at address 0x80002 to the code word 00101. Because the code word 00101 after changing the idr_pic_id is two bits longer than the code word 011 of the original idr_pic_id, all data from address 0x80002 and beyond must also be shifted two bits in the rewriting process. 
     This bit shifting process must also be applied to all recording media that manages data of several bit length with linear address, including primary recording media such as semiconductor memory and secondary recording media such as hard disk drives. 
     As described above, when connecting plural byte streams that are encoded according to the H.264 standard, the idr_pic_id contained in the slice header on the recording medium must be rewritten in order to assure compatibility and the ability to reproduce the streams. However, when the idr_pic_id must be rewritten to a code word of a different length, the bit shifting process described above must be run and the data area must be rewritten. A problem with rewriting the data area is that processing can take a long time when CPU power is limited or the access speed of the recording medium is slow. Another problem is that when it is desirable to limit rewriting the recording medium, such as with optical disc media, rewriting the medium more than necessary can shorten the usable service life of the recording medium. These same problems can also be caused by rewriting the pic_parameter_set that is also contained in the slice header. 
     The present disclosure is directed to solve the above problems, and has an purpose to provide an editing device capable of suppressing the CPU processing load and the number of times of rewriting the recording medium, when connecting the byte streams. 
     A coding device according to the present disclosure is a device for encoding an input digital signal to generate a stream. The coding device includes a coding unit operable to encode an input digital signal using code words contained in one of plural code word groups each including variable length code words, and a multiplexer operable to generate the stream by generating parameters describing specific information about the streams, encoding the parameters, and adding the encoded parameters to the output data from the coding unit. The length of the code words contained in any single code word group is the same. The multiplexer selects one code word group containing three or more code words out of the plural code word groups, and codes the parameter using one code word selected from the code words contained in the selected code word group. 
     An editing device according to the present disclosure is a device for connecting first and second streams containing variable length coded parameters. The editing device includes a decision unit operable to compare an encoded first parameter contained in the first stream with an encoded second parameter contained in the second stream, and decide whether at least one of the first parameter and the second parameter is to be changed, and a replacing unit operable to replace at least one of the first and second parameters with the other code word of the same length as the code words assigned to the first and second parameters, when the decision unit decides that at least one of the parameters is to be changed. 
     The coding device substantially eliminates unnecessary data rewriting operations when connecting streams (such as H.264 standard byte streams) containing variable length coded parameters because even if a parameter is changed the code length of the parameter is not changed. 
     According to the editing device, if a header containing a variable length coded parameter must be rewritten when connecting streams, and compatibility can be assured by using code words having the same code length as the original header that is rewritten, the editing device replaces the code word in the header where the streams are connected with a code word of the same length. On the contrary, if a code word of the same code length is not available, the editing device rewrites the header so that the data length of a specific data unit does not change. The present disclosure thus affords a coding device that does not cause rewriting more data than necessary as a result of rewriting the header, reduces the load on the CPU when editing and connecting streams, and reduces the number of recording medium write operations. 
     Other objects and attainments together with a fuller understanding of the present disclosure will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a video coding circuit in a first embodiment of the present disclosure. 
         FIG. 2  describes coding the idr_pic_id in the first embodiment of the present disclosure. 
         FIG. 3  describes the process of connecting streams in the first embodiment of the present disclosure. 
         FIG. 4  shows a video recording device in the first embodiment of the present disclosure. 
         FIG. 5  is a block diagram of the video recording device in the first embodiment of the present disclosure. 
         FIG. 6  shows the table for storing and managing picture parameter sets in a second embodiment of the present disclosure. 
         FIG. 7  describes coding the pic_parameter_set_id in the second embodiment of the present disclosure. 
         FIG. 8  describes the process of connecting streams in the second embodiment of the present disclosure. 
         FIG. 9  describes the process of connecting streams in the second embodiment of the present disclosure. 
         FIG. 10  shows a video editing device according to a third embodiment of the present disclosure. 
         FIG. 11  is a block diagram of the video editing device according to the third embodiment of the present disclosure. 
         FIG. 12  shows an example of the editing window displayed in the video editing device according to the third embodiment of the present disclosure. 
         FIG. 13  is a flow chart of the stream connection process in the third embodiment of the present disclosure. 
         FIG. 14  is a flow chart of the SPS and PPS reading and generating step in the third embodiment of the present disclosure. 
         FIG. 15  is a flow chart of the ID rewriting process in the third embodiment of the present disclosure. 
         FIG. 16  describes the ID rewriting process in the third embodiment of the present disclosure. 
         FIG. 17  describes the ID rewriting process in the third embodiment of the present disclosure. 
         FIG. 18  shows the volume structure of the FAT file system in the third embodiment of the present disclosure. 
         FIG. 19  shows the data structure of the FAT file system in the third embodiment of the present disclosure. 
         FIG. 20  describes recording streams as files to a recording medium in the third embodiment of the present disclosure. 
         FIG. 21  shows the SPS syntax of the H.264 standard. 
         FIG. 22  shows the PPS syntax of the H.264 standard. 
         FIG. 23  shows the slice header syntax of the H.264 standard. 
         FIG. 24  shows the coding rules for variable length coding the ue(v) Descriptor. 
         FIG. 25  shows the coding rules for variable length coding the se(v) Descriptor. 
         FIG. 26  shows the syntax of the NAL unit in the H.264 standard. 
         FIG. 27  shows the syntax of the slice layer in the H.264 standard. 
         FIG. 28  shows the syntax of the slice data in the H.264 standard. 
         FIG. 29  shows the syntax of the byte stream NAL unit in the H.264 standard. 
         FIG. 30  describes the basic byte stream connection process of the first embodiment of the present disclosure. 
         FIG. 31  describes stream editing according to the prior art. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Preferred embodiments are described below with reference to the accompanying figures. 
     Embodiment 1 
     1. Configuration of Video Coding Device 
     The present embodiment describes below a video coding device that controls byte stream coding when connecting a plurality of byte streams which are encoded using IDR (Instantaneous Decoding Refresh) pictures so that necessity to rewrite the idr_pic_id which is the IDR picture identifier (ID) with a code word of a different code length does not occur. 
       FIG. 1  shows the video coding circuit included in the video coding device according to this embodiment of the present disclosure. This video coding circuit  700  includes a header generator and multiplexing circuit  701 , a DCT circuit  710 , an inverse DCT circuit  711 , a quantization circuit  720 , an inverse quantization circuit  721 , a quantization step selection circuit  730 , an entropy coding circuit  740 , a intra prediction circuit  750 , a inter prediction circuit  760 , a motion prediction circuit  761 , and a deblocking filter circuit  770 . The motion prediction circuit  761  and the inter prediction circuit  760  are not needed when encoding only IDR pictures. 
     2. Operation of Video Coding Circuit 
     The operation of the video coding circuit  700  is described next. 
     Coding an intra macroblock that can be decoded using only data contained in the same frame is described first. A macroblock is generally a 16×16 block of pixels, and includes a plurality of blocks that are the unit for DCT and intra prediction coding. 
     The pixel difference value is calculated for each pixel between macroblock (“target macroblock”) that is to be encoded in the input digital video signal  790  and target macroblock predicted by the intra prediction circuit  750 , resulting in a 16×16 block of pixel difference values. 
     The DCT circuit  710  applies a DCT process to the block of difference values. This process is normally applied to 4×4 or 8×8 pixel blocks, and outputs the frequency component conversion coefficient. The conversion coefficient is input to the quantization circuit  720  and quantized. The quantized conversion coefficient is then encoded by the entropy coding circuit  740 . Entropy coding in the H.264 standard uses either context-adaptive variable length coding (CAVLC) or context-adaptive binary arithmetic coding (CABAC). The code size after entropy coding is input to the quantization step selection circuit  730 . 
     The quantization step selection circuit  730  controls the value of the quantization step of the quantization circuit  720  so that the resulting code size goes to a target code size. After quantization the coefficient is also decoded by the inverse quantization circuit  721  and the inverse DCT circuit  711  and input to the intra prediction circuit  750 . The intra prediction circuit  750  generates predicted pixel values for the neighboring macroblocks that are encoded later. 
     Coding the inter macroblocks using inter-frame prediction is described next. The motion prediction circuit  761  applies a matching process to the block currently being coded (the block that is the unit used for motion compensation) and the pixels of the reference frame, and calculates the vector resulting in the least error. The error between the predicted pixel values of the target macroblock output by the inter prediction circuit  760  based on the result of the motion prediction and the pixel values of the target macroblock in the input digital video signal  790  is calculated and input to the DCT circuit  710 . The process after input to the DCT circuit  710  is basically the same as for intra macroblock coding. In inter coding, however, a deblocking filter circuit  770  is commonly used to reduce visible block distortion. 
     The header generator and multiplexing circuit  701  generates the slice header, adds the slice header to the slice data encoded by the entropy coding circuit  740 , and outputs the result as a byte stream NAL unit  791 . The header generator and multiplexing circuit  701  incorporates the idr_pic_id in the slice header at this time. 
     In the video coding circuit  700  according to this embodiment of the present disclosure, the header generator and multiplexing circuit  701  assigns the code words according to the coding rules shown in  FIG. 24  when adding the idr_pic_id to the picture. The coding rules shown in  FIG. 24  divide the data values (codeNum) into a number of ranges (groups), and the code word length is the same in each range (group), but the length of the code words in one range (group) differs from the code word length in each other range (group). For example, the code words for all data values in the range 3 to 6 are 5 bits long, but the code words for all data values in the range 7 to 14 are 7 bits. 
     More specifically, to add the idr_pic_id, the video coding circuit  700  (more particularly, the header generator and multiplexing circuit  701 ) in this embodiment of the present disclosure selects one range where there are three or more code words in a range of plural codeNum values, selects one of plural code words contained in the selected range, and assigns the selected code word to the idr_pic_id. For example, referring to  FIG. 24 , one of the codeNum ranges each of which includes code words of 5 or more bits long is selected. That is, one of the codeNum ranges corresponding to “001x 1 x 0 ”, “0001x 2 x 1 x 0 ”, and “00001x 3 x 2 x 1 x 0 ”, . . . , is selected. If the range of data values 3 to 6 (0010x 1 x 0 ) is selected, the value of the idr_pic_id is assigned 3, 4, 5, or 6. 
       FIG. 2  describes an example of assigning the idr_pic_id when the range of codeNum 3-6 is selected to assign the idr_pic_id. When generating stream A ( 150 ) and stream B ( 160 ), the video coding circuit  700  determines the value of the idr_pic_id assigned to the slice header of the i-th (where i is an integer greater than 0) IDR picture from the following equation
 
idr_pic_id=3+( i %3)
 
where % is an operator that returns the remainder.
 
     In the H.264 standard requires that the idr_pic_id is different in adjacent IDR pictures. As shown in  FIG. 24 , if the codeNum is a value of 3 to 6, the code word of idr_pic_id is 5 bits long. The code word length therefore will not change if the value of the idr_pic_id is rewritten using code words in the same range. Therefore, if substream a ( 153 ) and substream b ( 163 ) shown in  FIG. 2  are connected using this coding method and the pictures #m+3 and #n that are adjacent where the streams are connected would have the same idr_pic_id, the idr_pic_id can be easily changed to a different value. In this example both picture #m+3 and picture #n have the same idr_pic_id (3 in this example), and the idr_pic_id of picture #n+1 is 4. The idr_pic_id of picture #n is therefore changed to 5. By using a value in a codeNum range where there are three or more codes of the same length, the idr_pic_id of picture #n can be rewritten to a value (5 in this example) of the same length that is different from the idr_pic_id of the adjacent pictures #m+3 and #n+1. Note that while both substream a ( 153 ) and substream b ( 163 ) in  FIG. 2  are four pictures long, it will be obvious that the idr_pic_id can be rewritten in the same way regardless of the number of pictures in the substream. 
     The video coding circuit  700  in this embodiment of the present disclosure does not need to use the same codeNum range that is used to assign the idr_pic_id for all encoded streams. Selecting the same range is only necessary when the parameters such as the horizontal pixel count, vertical pixel count, and bit rate of the pictures are the same, or when the connection is significant. For example, the content could be encoded at two different bit rates, a high bit rate and a low bit rate, where the high bit rate stream is the primary content and the low bit rate stream is used for video previews. Because there is no need to connect the low bit rate streams in this case, an idr_pic_id=i %2 could be used to minimize the code length of the low bit rate content while an idr_pic_id=3+(i %3) could be used for the high bit rate content. 
     3. Recording Device 
       FIG. 4  shows a video recording device that has the video coding circuit  700  described above. This video recording device  600  encodes video and audio information input through the lens  691  and microphone  692  by means of the incorporated video coding circuit  700 , and records the encoded streams to the recording medium  500  inserted to a drive  690 . 
       FIG. 5  is a block diagram of the video recording device  600 . As shown in  FIG. 5  the video recording device  600  has a lens  691 , a microphone  692 , an imaging element  687 , A/D conversion circuits  688  and  689 , an audio processing circuit  686 , a CPU  681 , memory  682 , a nonvolatile memory  683 , a bus controller  685 , and the video coding circuit  700 . The CPU  681  controls operation of the video recording device  600 . The nonvolatile memory  683  stores the programs run by the CPU  681 . The bus controller  685  controls input/output to the recording medium  500 . 
     A light for video information is focused on the imaging element  687  by the lens  691 . The imaging element  687  converts the imaged information to an electric signal. The A/D conversion circuit  688  converts the electric signal to a digital video signal. The video coding circuit  700  then encodes the digital video signal to a H.264 standard byte stream, and records the byte stream to the recording medium  500 . The byte stream recorded to the recording medium  500  can then be edited by an editing device (described below) after recording is completed. 
     4. Conclusion 
     As described above, this embodiment of the present disclosure affords a video coding device that can reduce the processor load during editing when connecting plural byte streams that are coded using IDR pictures. 
     This embodiment of the present disclosure is described assuming that all of the pictures are IDR pictures, but the present disclosure is not so limited. It will be obvious that the present disclosure can be used when the assumptions described above are not true, such as when the adjacent pictures where the two streams are connected are IDR pictures. 
     The foregoing embodiment is also described assuming that the code size of all pictures is the same or the buffer constraints of the virtual reference decoder can be maintained, but the following operation can also be used by the video editing device to meet the buffer constraints.
         If the buffer occupancy VA after substream a ( 153 ) ends is greater than the buffer occupancy VB just before substream b ( 163 ) starts before the connection of the stream, (VA−VB) bytes of trailing_zero_8bits (padding bits) can be inserted immediately after the end of substream a ( 153 ) so that buffer occupancy becomes VB.   If VA is less than VB, several pictures at the end of substream a ( 153 ) can be re-encoded, for example, so that buffer occupancy becomes VB.       

     This method makes the concept of the present disclosure available regardless of the above assumptions. 
     This embodiment of the present disclosure also assumes that the SPS or PPS is located only at the beginning of the byte stream, but the PPS does not need to be at the beginning of the byte stream, and if the SPS of substream b ( 163 ) is not the same as the SPS of substream a ( 153 ), it does not need to be at the beginning. 
     The present disclosure is described using coding the idr_pic_id by way of example, but the present disclosure can be used to encode syntax coded in VLC for any parameter including SPS, PPS, and a slice header. This embodiment also assumes that a byte stream is present, but embodiments that multiplex NAL units are not so limited. 
     Embodiment 2 
     The present embodiment describes below a video coding device that connects and encodes plural byte streams without necessity to rewrite the pic_parameter_set_id that is identifier of the PPS (picture parameter set). This embodiment is particularly useful when connecting a plurality of byte streams in which plural PPS are coded. The basic configuration of the video coding device is the same as in the first embodiment of the present disclosure described above. 
     In this embodiment of the present disclosure the header generator and multiplexing circuit  701  stores and manages the combinations of PPS content and pic_parameter_set_id (“PPSID”) values. More specifically, if the syntax is different for all encoded PPS in the streams generated by the video coding device according to this embodiment of the present disclosure, the coding process assigns a different PPSID to each PPS. 
       FIG. 6  is a table for storing and managing the PPS in the header generator and multiplexing circuit  701 . When the PPS syntax value is different, a different PPSID is assigned. If a PPS having pic_init_qp_minus26=10 and the same syntax as PPS with PPSID=0 except pic_init_qp_minus26 is created, a new PPS with PPSID=1 is added. Similarly, if a PPS having chroma_qp_index_offset=3 and the same syntax as PPS with PPSID=0 except chroma_qp_index_offset is created, a new PPS of PPSID=2 is added. If a PPS having pic_init_qp_minus26=10 and chroma_qp_index_offset=3 and the same syntax as PPS with PPSID=0 except pic_init_qp_minus26 and chroma_qp_index_offset is created, the created PPS differs from the PPS of PPSID=0, 1, and 2, and thus a PPS of PPSID=3 is added. The PPS management table is thus updated so that a unique PPSID is assigned to the PPS. The header generator and multiplexing circuit  701  of the video coding device can assign unique, non-duplicating PPSID values with reference to a PPS management table such as shown in  FIG. 6 . 
     With reference to  FIG. 7 , the process of the header generator and multiplexing circuit  701  assigning the PPSID is described next. If two different PPS of PPSID=0 and 1 are required for coding in stream A ( 150 ), the two PPS are output and the PPSID value to be referred to in the slice header is output. Similarly, for coding stream B ( 160 ), if three different PPS of PPSID=0, 2, and 3 are needed, the three PPS are output and the PPSID value to be referred to in the slice header is output. What is essential is that the PPSID values are defined uniquely throughout both stream A ( 150 ) and stream B ( 160 ). 
       FIG. 8  describes an example of connecting substream a ( 153 ) and substream b ( 163 ) in  FIG. 7  using the video editing device. First, all PPS that are required after the streams are connected are output. Because the PPSID in the slice headers are unique if the video coding device according to this embodiment of the present disclosure is used. Thus the streams can be connected without rewriting the variable length coded PPSID values. Because the processing load of rewriting the PPSID to different length code words increases proportionally to the stream length, the present disclosure is particularly effective because there is no need to rewrite the PPSID parameters. 
     The PPS is output immediately after the SPS in  FIG. 7  and  FIG. 8 , but the PPS can be inserted just before the picture containing the first PPSID as shown in  FIG. 9 . As described in the fourth embodiment below, a unique PPSID is not always assigned to all streams encoded by the video coding device of this embodiment as shown in  FIG. 6 . A unique PPSID can be selected only when the parameters such as the horizontal pixel count, vertical pixel count, and bit rate of the pictures are the same, or when the connection is significant. 
     As described above, this embodiment of the present disclosure affords a video coding device that can reduce the processor load when connecting a plurality of byte streams containing a plurality of encoded picture parameter sets. 
     Embodiment 3 
     This embodiment of the present disclosure describes a video editing device that can encode the IDR pictures without duplicating the idr_pic_id of the pictures at the seam and can minimize the area on the recording medium where the values are rewritten when connecting a plurality of byte streams encoded with IDR pictures. 
     1. Configuration of the Video Editing Device 
       FIG. 10  shows a video editing device according to this embodiment of the present disclosure. This video editing device  501  is rendered using a computer  502 . The computer  502  has an internal drive  590  or an external drive  591  for accessing the recording medium  500  containing video data. The recording medium  500  is a computer-readable medium such as a memory card, an optical disc, or a removable hard disk drive, for example. The computer  502  could be connected by a network cable  594  or wirelessly to a network for sending and receiving video data. A display  592  and input device  593  such as a mouse and keyboard are also connected to the computer  502  for video editing by the user. 
       FIG. 11  is a block diagram of the video editing device  501 . The video editing device  501  has a CPU  581 , a memory  582 , a hard disk drive  583  for storing programs and the operating system (OS), and an internal bus  584  connecting these and other devices. The hard disk drive  583  stores programs and the operating system. The video editing device  501  also has a bus controller  585  for connecting the recording medium  500 , a network controller  588  for inputting and outputting video data over a network, a graphics controller  587  for connecting the display  592 , and an input device controller  586  for connecting the input device  593 . 
     The recording medium  500  could be connected using an ATA (AT Attachment) or USB (Universal Serial Bus) interface, for example. The OS and programs are stored on the hard disk drive  583 , and are loaded into the memory  582  and run by the CPU  581  as needed. The video editing function of the video editing device  501  is achieved by an appropriate program running under the OS. 
     An example of a window screen displayed on the display  592  of the video editing device  501  is shown in  FIG. 12 . The display  592  displays a time line  571  for video editing, a time line  572  for audio editing, a preview window  573  for displaying reproduced video content, and a bin window  574  for displaying a list of the captured video contents. Byte streams are connected by the user selecting a plurality of video content streams displayed in the bin window  574  using the input device  593  and dragging them into the video time line  571  to output (render) the finished file. 
     The following description of this process assumes that the substream a ( 153 ) and substream b ( 163 ) shown in  FIG. 30  are stored to a recording medium such as the memory  582 , the hard disk drive  583 , the recording medium  500 , or a network drive connected by the network controller  588  shown in  FIG. 11 . A byte stream C ( 170 ) connecting substream a ( 153 ) and substream b ( 163 ) is generated on such a recording medium. As a result, the byte stream C ( 170 ) can ideally be generated by simply rewriting the directory management information on the recording medium sc that substream a ( 153 ) and substream b ( 163 ) are connected. 
     This embodiment of the present disclosure is directed to an ID rewriting process for rewriting the idr_pic_id. The process for rewriting the idr_pic_id is done as follows. When connecting a plurality of byte streams encoded using IDR pictures, the ID rewriting process changes the picture ID (idr_pic_id) of the pictures adjacent to the seam so that the idr_pic_id values are not the same and can be different by rewriting the smallest area possible on the recording medium. 
     2. Stream Connection Process 
     The stream connection process of the video editing device according to this embodiment of the present disclosure is described next with reference to the flow chart in  FIG. 13 . 
     First, the process of reading and generating the SPS and PPS is done (S 11 ). In this example the SPS-BNU  151  of stream A ( 150 ) and the SPS-BNU  161  of stream B ( 160 ) are read to generate the SPS-BNU  171  of byte stream C ( 153 ). If the SPS-BNU  171  of byte stream C ( 153 ) is the same as the SPS-BNU  151  of stream A ( 150 ) or the SPS-BNU  161  of stream B ( 160 ), there is no need to create a new SPS-BNU  171  on the recording medium. The PPS-BNU  152  of stream A ( 150 ) and the PPS-BNU  162  of stream B ( 160 ) are similarly read to generate the PPS-BNU  172  of byte stream C ( 170 ). 
     The ID (id_Alast) of the last picture in substream a ( 153 ) is then read (step S 12 ), the ID (id_B1) of the first picture in substream b ( 163 ) is read (step S 13 ), and the ID (id_B2) of the second picture in substream b ( 163 ) is read (step S 14 ). 
     The stream ID, that is, idr_pic_id, can be acquired as follows. 
     First, the stream is searched for start_code_prefix_one_3bytes ( FIG. 29 ) and the value of nal_unit_type contained in the NAL unit ( FIG. 26 ) is determined to find the NAL unit containing the slice layer. The idr_pic_id can be found by interpreting the slice header of the slice layer. 
     The ID is then rewritten (S 15 ). This process rewrites the idr_pic_id if the idr_pic_id is the same in the adjacent pictures. The directory management information is then updated (step S 16 ). This process connects the SPS, PPS, substream a ( 153 ), and substream b ( 163 ) into a single stream, and ends. 
     The directory management information is also updated to add an SPS and PPS to the parts of stream A ( 150 ) other than substream a ( 153 ) and to the parts of stream B ( 160 ) other than substream b ( 163 ) to render a byte stream. 
     The process of reading and generating the SPS and PPS (step S 11  in  FIG. 13 ) is described next with reference to the flow chart in  FIG. 14 . 
     The SPS  110  of stream A ( 150 ) and the SPS of stream B ( 160 ) are read (S 111 , S 112 ). The two SPS are compared to determine if they can be shared (S 113 ). This determination is done as follows. 
     First, if the two SPS are identical byte trains, it is determined that they can be shared. Second, if only the seq_parameter_set_id of the two SPS is different, it is determined that the SPS can be shared and the seq_parameter_set_id is set to seq_parameter_set_id value of either one of the two SPS. In any other case, it is determined that they cannot be shared. If it is determined that the SPS can be shared, the common SPS is output (S 114 ). If it is determined that they cannot be shared, the SPS of stream A and the SPS of stream B are output (S 119 , S 120 ). 
     The PPS of stream A ( 150 ) and the PPS of stream B ( 160 ) are read (S 115 , S 116 ). The two PPS are compared to determine if they can be shared (S 117 ). This determination is done as follows. 
     First, if the two PPS are identical byte trains, it is determined that they can be shared. However, if the seq_parameter_set_id values of the SPS are different in step S 113 , the PPS will never be identical byte trains. Second, if only the pic_parameter_set_id of the two PPS is different, it is determined that the PPS can be shared and the pic_parameter_set_id is set to the pic_parameter_set_id value of either one of the two PPS. In any other case, it is determined that they cannot be shared. If it is determined that the PPS can be shared, the common PPS is output (S 18 ). If it is determined that they cannot be shared, the PPS of stream A and the PPS of stream B are output (S 121 , S 122 ). 
     If the parts of stream A ( 150 ) other than substream a ( 153 ) and the parts of stream B ( 160 ) other than substream b ( 163 ) are to be left as a byte stream on the recording medium, a number of SPS and PPS determined by the final number of streams on the recording medium must be output to the recording medium  500 . 
     The process of rewriting the picture ID (step S 15  in  FIG. 13 ) is described next with reference to the flow chart in  FIG. 15 . 
     The CPU  581  compares the ID (id_B1) of the first picture in substream b with the ID (id_Alast) of the last picture in substream a, and determines if they overlap (are the same) (S 151 ). If the IDs don&#39;t overlap, the ID rewriting process ends. If the IDs overlap, operation continues as described below. 
     It is determined if there is an ID that has the same code length as id_B1 and is not the same as id_Alast or id_B2 (S 152 ). Using VLC as shown in  FIG. 24 , for example, if id_Alast=7, id_B1=7, and id_B2=10, there are values 8, 9, 11, 12, 13, 14 as ID (code words) that have the same code length as id_B1 and are different from id_Alast or id_B2. If such an ID is available, id_B1 is rewritten to that ID (S 157 ). If such an ID is not available, such as when id_Alast=1, id_B1=1, and id_B2=2, the length of the slice header can be changed. In this case, a code word contained in a codeNum range different from id_Alast and id_B1 is assigned to id_B1. 
     Then, it is determined if the entropy_coding_mode_flag is equal to 1 and cabac_alignment_one_bit is equal to or more than 1 in all slices contained in the first picture in substream b ( 163 ) (S 153 ). When using context-adaptive binary arithmetic coding (CABAC) (that is, entropy_coding_mode_flag=1), there are cabac_alignment_zero_bit for one or more bits shown in  FIG. 28  at the beginning of the slice data if the end of the slice header is not aligned in byte units. If cabac_alignment_one_bit≧1 in all slices contained in the first picture in substream b ( 163 ), the cabac_alignment_one_bit for one bit is reduced so that the id_B1 can be replaced with a code word that is only one bit longer than the existing code length without shifting the large slice data. 
     As shown in  FIG. 16 , id_B1 is rewritten to an ID of the size (code length of the current id_B1+1 bit), and the slice header  120  up to right before the cabac_alignment_one_bit is shifted 1 bit (S 159 ). An ID of the size (code length of the current id_B1+1 bit) will thus never duplicate id_Alast or id_B2. In this case one cabac_alignment_one_bit is deleted. Note that in the step S 158  id_B1 could be replaced with a codeword which is N bits (where N is a natural number≦7) longer than the current code word. In this case, N units of cabac_alignment_one_bit in the slice are deleted. 
     If the step S 153  returns No, it is determined if the number of trailing_zero_8bits in the picture is greater than or equal to the number of slices in the picture (S 154 ). The trailing_zero_8bits are located after the end of the NAL unit (nal_unit) shown in  FIG. 29 , and therefore there are 0 or more trailing_zero_8bits at the end of each slice layer. As shown in  FIG. 17 , if the number of trailing_zero_8bits in the first picture in substream b ( 163 ) is greater than or equal to the number of slices in the picture, id_B1 is rewritten to an ID of size (code length of current id_B1+8 bits) (S 160 ), and slice layer data before the trailing_zero_8bits is shifted by 8 bits (=1 byte) (step S 161 ). In the example shown in  FIG. 17 , the total code length of slice #1 does not change if one trailing_zero_8bits immediately following slice #1 is reduced. 
     Even if there are no trailing_zero_8bits immediately after the slice layer, as in slice #1 to #3, slice #1 can be shifted by one byte, slice #2 shifted by two bytes, slice #3 shifted by three bytes, and slice #4 shifted by four bytes, and four units of trailing_zero_8bits following slice #4 can be reduced. Because this process does not change the code length of the picture, there is no effect on the downstream pictures. 
     Referring again to  FIG. 15 , if the number of trailing_zero_8bits in the picture is less than the number of slices in the picture, the code length of the picture increases. The step S 154  replaces id_B1 with an ID of size (code length of current id_B1+8 bits), but the code length is not limited to this length. Setting the size of the code word to (code length of current id_B1+8 bits) is attributed to simplifying the process because the slice layer data can be simply shifted in byte units. The slice layer data is shifted by the increase in the code length in step S 155  (S 156 ). This process continues until the increase in the code length using trailing_zero_8bits is absorbed or continues upto the end of the substream b ( 163 ). The increase in the code words can also be set to an integer multiple of 8 bits (=1 byte). 
     Updating the directory management information in step S 16  in  FIG. 13  is described using cluster management information by way of example. 
     Cluster management information records information on link between clusters where data for each file is stored on disc, similarly to the file allocation table (FAT) in a FAT file system. The cluster is the access unit used for managing the areas where files (streams) are stored. The recording area of one file (stream) is a set of clusters. 
       FIG. 18  shows the volume structure of a FAT file system. This figure shows an area structure in which e logical drive  801  set inside the physical drive  800  such as the recording medium  500  is formatted in the FAT file system. The file allocation table  804  is a table of cluster numbers  143  as shown in  FIG. 19 , and shows the links between the data parts  144  of a cluster unit recorded in the user data area  806 .  FIG. 19  shows an example of clusters  3 ,  4 , and  7  composing a single file  145 . 
     When the ID (parameter) is rewritten, data is rewritten only for the clusters with that ID. In the directory management information updating process (step S 16 ) in this embodiment of the present disclosure, the links between the clusters corresponding to the recording areas of the SPS, PPS, substream a ( 153 ), and substream b ( 163 ) are changed in the file allocation table  804  to connect the SPS, PPS, substream a ( 153 ), and substream b ( 163 ) into a single file. 
     With reference to  FIG. 20 , a case in which the video coding device records the streams used in this embodiment as files to a recording medium, such as a hard disk, an optical disc, is described below. 
     As shown in  FIG. 20 , stream A ( 150 ) and stream B ( 160 ) are recorded to the recording medium  500  so that the beginning of the data for each picture is aligned with the beginning of the file system recording unit which is a cluster  141  in this embodiment. This embodiment of the present disclosure is particularly effective when the end of substream a ( 153 ) and the beginning of substream b ( 163 ) are thus recorded in alignment because the connected streams do not need to be rewritten. If the end of a picture data block is not aligned with a cluster boundary  142  when the video is encoded by the video coding device, stuffing bytes (trailing_zero_8bits)  131  of invalid data are added. The recorded substream a ( 153 ) and substream b ( 163 ) are connected in the method described above. 
     The unit that is aligned with the cluster  141  is not limited to a picture. Slices, GOPs (Group of Pictures) or other unit whereby streams can be connected can be used. 
       FIG. 20  shows two slices included in one picture, but the present disclosure can obviously be used with any number of slices. This embodiment of the present disclosure is described with the beginning of a picture aligned with the cluster boundary, but the present disclosure can also be used with the beginning of a GOP or other stream editing unit aligned with the cluster boundary. The seam where substream a ( 153 ) and substream b ( 163 ) are connected can also be aligned with the cluster boundary. 
     3. Conclusion 
     As described above when streams (such as H.264 standard byte streams) containing variable length coded parameters (idr_pic_id) are connected and interchangeability can be assured using code words of the same code length as the variable length code word for the parameter, this embodiment rewrites the code word of the parameter in the header of the pictures at the seam, and minimizes the processor load required to rewrite the data if a code word of the same length is not available. This can provide a video editing device that can connect a plurality of byte streams that are encoded using IDR pictures without duplicating the idr_pic_id in adjacent pictures and minimize the area where values are rewritten on the recording medium. The area where values are rewritten can be minimized because of the following reasons. 
     1) When the id_B1 can be rewritten with a code word of the same length (S 157 ), only the idr_pic_id needs to be rewritten for all slices contained in the picture. 
     2) When a code word of the same length is not available (S 158 ), cabac_alignment_one_bit can be used so that rewriting the large slice data is not necessary. 
     3) If rewriting the slice data is necessary (S 155 ), the slice data can be shifted in byte units by shifting id_B1 by 8 bits. 
     This embodiment of the present disclosure describes the case of rewriting the ID of the first picture in substream b ( 163 ), but it will be obvious that the same procedure can be used to rewrite the ID of the last picture in substream a ( 153 ) instead. If using substream a ( 153 ) can lighten the load of the ID rewriting process (S 15 ), rewriting the ID of the last picture in substream a ( 153 ) is preferable. 
     This embodiment of the present disclosure is described the case of using trailing_zero_8bits, but cabac_zero_word can be used instead of trailing_zero_8bits, or invalid data in the system stream containing the NAL unit can be used. 
     The process of connecting streams according to the H.264 standard is used by way of example above, but the present disclosure can be used with any video editing device that rewrites a variable length coded syntax. A device having a CPU  581  and memory  582  as shown in  FIG. 11 , and an OS and programs running on the video editing device is considered as the video editing device, however it will be obvious that the means of executing the connection process described above is not limited to this hardware configuration. 
     Embodiment 4 
     This embodiment of the present disclosure is the video editing device of the third embodiment modified to correctly rewrite pic_parameter_set_id and minimize the area required to rewrite the values on the recording medium when connecting plural byte streams. The operation of this video editing device is basically the same as the operation of the third embodiment described in the flow charts in  FIG. 13  to  FIG. 15 , differing in that the pic_parameter_set_id parameter is substituted for the idr_pic_id parameter. 
     An extreme example to which this embodiment of the present disclosure is applied is when the PPS describing the specific picture parameters is different between substream a ( 153 ) and substream b ( 163 ), and the same pic_parameter_set_id is used. In this case, the step S 117  in the SPS/PPS reading and generating process S 11  shown in  FIG. 14  determines that the PPS cannot be shared, and the step S 122  outputs a PPS with the changed pic_parameter_set_id in the PPS of stream B. Because the pic_parameter_set_id of the PPS is changed, the pic_parameter_set_id referenced in the slice header of all pictures in substream b ( 163 ) must also be changed. The process for changing the variable length coded pic_parameter_set_id in all slices of substream b ( 163 ) might require shifting the entire stream if rewriting to a same-length code word of a different value is not possible. The present disclosure minimizes the shifting process and is therefore extremely useful. 
     As described above this embodiment of the present disclosure affords a video editing device that can correctly rewrite pic_parameter_set_id and minimize the area required to rewrite the values on the recording medium when connecting plural byte streams. 
     The present disclosure can be advantageously used in video coding devices such as digital camcorders and recorders, and in video editing devices for editing video streams recorded by digital camcorders and recorders. 
     Although the present disclosure has been described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present disclosure as defined by the appended claims, unless they depart therefrom. This application is related to Japanese Patent Application No. 2006-154264, filed on Jun. 2, 2006, the content of which is incorporated herein by reference.