Patent Publication Number: US-6671323-B1

Title: Encoding device, encoding method, decoding device, decoding method, coding system and coding method

Description:
TECHNICAL FIELD 
     The present invention relates to an encoding system for encoding input video data and a decoding system for decoding encoded streams. 
     BACKGROUND ART 
     Recently, in order to compress/encode video data, the MPEG (Moving Picture Experts Group) technology standardized as ISO/IEC 13818 has come into common use at broadcasting stations that produce and broadcast television programs. MPEG is becoming the de facto standard especially for recording video data generated by video cameras or the like, on tape, disks, or other recording media that can be accessed randomly or for transmitting video programs produced at broadcasting stations, via cables or satellites. 
     The MPEG technology is an encoding technology that can improve compression efficiency by means of predictive coding of pictures. More particularly, the MPEG standard employs a plurality of predictive coding systems that combine intra-frame prediction and inter-frame prediction, and each picture is encoded by means of either of the following picture types: I-picture (Intra Picture), P-picture (Predictive Picture), and B-picture (Bidirectionally Predictive Picture) according to the prediction system. The I-picture, which is not predicted from other pictures, is a picture encoded within the frame. The P-picture is a picture subjected to inter-frame forward predictive coding by a preceding (past) I-picture or P-picture. The B-picture is a picture subjected to bidirectionally predictive coding both by a preceding (past) I-picture or P-picture and by a following (future) I-picture or P-picture. 
     FIG. 1 shows an example of a video processing system used within a broadcasting station or between broadcasting stations. As described above, it has been proposed to use a MPEG encoder and MPEG decoder as shown in FIG. 1 to transmit source video data from a first video processor  1  provided as a sending system to a second video processor  4  provided as a receiving system within or between broadcasting stations. 
     The first video processor  1  receives source video data such as component-type base-band video of the D 1  format and performs edit processing, special-effects processing, synthesis processing or the like on the source video data. The video processor  1  also receives ancillary data such as closed captions and teletext data and adds the ancillary data to the blanking intervals of the source video data. Therefore, ancillary data has been embedded in the blanking intervals of the video data output from the video processor  1 . 
     The MPEG encoder  2  receives the video data from the video processor  1  and encodes it to generate an encoded stream. Such an encoded stream is also known as an elementary stream. As everyone knows, television signals have vertical and horizontal blanking intervals on four sides of the actual video data area called the active video area and the ancillary data described above has been inserted in the blanking intervals. 
     However, the MPEG standard specifies that only the active video area where pixels actually exist must be encoded. Thus, the encoded stream is the data obtained by encoding only the active video area of input video data, but it does not contain ancillary data superimposed on the blanking intervals. In other words, when the input video data is encoded by the MPEG encoder  2 , the ancillary data superimposed on the input video data is lost. 
     The MPEG decoder  3  receives the encoded stream from the MPEG encoder and decodes it to generate decoded video data, which is then supplied to the second video processor  4 . Since the encoded stream supplied to the MPEG decoder  3  does not contain information on the ancillary data, naturally the decoded video data does not contain information on the ancillary data. 
     Thus, MPEG encoding and MPEG decoding performed when video data is transmitted from the sending system to the receiving system have the problem that the ancillary data added to the blanking intervals of the video data by the first video processor  1  is not transmitted from the sender or first video processor  1  to the receiver or second video processor  4  although the video data that corresponds to the active area can be transmitted. 
     Moreover, the fact that only the active video data is transmitted if MPEG encoding and MPEG decoding are performed when video data is transmitted from the sending system to the receiving system means that the information inherent to the source video data is not transmitted to the receiving system either. The information inherent to the source video data is the information possessed by the source video data itself, including the location of the blank areas or the location of the active video area with respect to the full pixel area. Specifically, this is the information as to from which vertical line in the full pixel area of the source video data the active video lines start and as to at which pixel in the horizontal direction of the full pixel area the active video area starts. 
     Now the processing of video data that has undergone 3:2 pull-down will be described with reference to FIG.  2 . The figure shows an example of a video processing system used within or between broadcasting stations to process both video data with a 24-Hz frame frequency and video data with a 30-Hz frame frequency. 
     The 3:2 pull-down circuit  5  receives video data that has a frame rate of 24 Hz (24 frames per second) and generates video data with a frame rate of 30 Hz (30 frames per second). The film material used at movie theaters and the like is recorded on optical films at a frame rate of 24 Hz (24 frames per second), which is entirely different from the 29.97-Hz frame rate of NTSC television signals. Thus, to convert film material to television signals, 30 frames are generated from 24 frames. 
     The 3:2 pull-down process will be described with reference to FIGS. 3A and 3B. FIG. 3A shows source video data with a frame rate of 24 Hz while FIG. 3B shows the 30-Hz video data after a 3:2 pull-down conversion. As shown in FIGS. 3A and 3B, the 3:2 pull-down process generates a repeat field t 1 ′ by repeating the top field t 1  in the first frame F 1  and generates a repeat field b 3 ′ by repeating the bottom field b 3  in the third frame F 3 . Thus, the 3:2 pull-down process converts video data with a frame rate of 24 Hz into video data with a frame rate of 30 Hz by converting 2 fields into 3 fields in a predetermined sequence. 
     As described with reference to FIG. 1, the first video processor  1  receives 30-Hz source video data and performs edit, special-effects, synthesis, and/or other operations on it. The video processor  1  also receives ancillary data such as closed captions and teletext data and adds it to the blanking intervals of the source video data. This addition of ancillary data is performed with respect to video data having a frame frequency of 30 Hz and the ancillary data is added to all the fields contained in the 30-Hz video data. That is, the ancillary data is added not only to the top fields (t 1 , t 2 , . . . ) and bottom fields (b 1 , b 2 , . . . ), but also to the repeat fields t 1 ′ and b 3 ′. 
     The 2:3 pull-down circuit  6  receives the 30-Hz video data generated by the 3:2 pull-down process described above and converts it into video data with a frame rate of 24 Hz. Specifically, as shown in FIG. 3C, the 2:3 pull-down circuit  6  is used to remove the repeat fields t 1 ′ and b 3 ′ inserted by the 3:2 pull-down process. The 2:3 pull-down process must be performed before MPEG encoding. This is because these repeat fields are the redundant fields inserted by the 3:2 pull-down process and can be deleted without any degradation in image quality, 
     The MPEG encoder  2 , which is the same as the MPEG encoder  2  described with reference to FIG. 1, receives 24-Hz video data from the 2:3 pull-down circuit  6  and encodes it to generate an encoded stream. 
     However, the MPEG standard specifies that only the active video area where pixels actually exist must be encoded. Thus, the encoded stream is the data obtained by encoding only the active video area of input video data, but it does not contain ancillary data superimposed on the blanking intervals. In other words, when the input video data is encoded by the MPEG encoder  2 , the ancillary data superimposed on the input video data is lost. 
     The MPEG decoder  3 , which is the same as the MPEG decoder  3  described with reference to FIG. 1, receives the encoded stream from the MPEG encoder and decodes it to generate decoded video data. According to the MPEG standard, the Repeat_first_field and Top_field_first flags are set in encoded streams as information about the frame structure. Since MPEG decoders process data based on these flags, the decoded video data has a frame rate of 30 Hz. 
     As can be seen from the above description, even if ancillary data is added to 30-Hz video data by the processor in the sending system, the repeat fields are removed from the 30-Hz video data after the 2:3 pull-down process necessary for MPEG encoding. That is, the ancillary data is removed together with the repeat fields to which it has been added. Therefore, if a 2:3 pull-down process is performed when video data is transmitted from the sending system to the receiving system, the information-about the ancillary data added to the repeat fields is not transmitted from the sender or first video processor  1  to the receiver or second video processor  4  because the repeat fields themselves are removed by the 2:3 pull-down process. 
     DISCLOSURE OF THE INVENTION 
     The present invention relates to an encoding system for encoding input video data and a decoding system for decoding the encoded streams. More particularly, it proposes a system and method for sending the ancillary data added to video data and the information inherent to the video data together with encoded streams in such a way that they will not be lost even if MPEG encoding and MPEG decoding are repeated. 
     The MPEG encoder extracts the ancillary data from the video data, inserts the extracted ancillary data into encoded streams as Ancillary_data, and thereby sends the ancillary data together with the encoded streams. The MPEG decoder extracts the ancillary data from the encoded streams and adds it to the base-band video data generated by MPEG decoding. 
     An encoding apparatus for encoding input video data extracts ancillary data that are added in the blanking intervals of the input video data from the input video data, encodes the input video data to generate encoded streams, and controls the above described encoding means so as to insert the above described ancillary data into the encoded streams. 
     A decoding apparatus for decoding the encoded streams generated by encoding input video data extracts ancillary data from the encoded streams, decodes the encoded streams to generate decoded video data, and multiplexes the ancillary data onto the blanking intervals of the decoded video data. 
     A decoding apparatus for decoding the encoded streams generated by encoding input video data parses the syntax of the encoded streams to obtain the ancillary data contained in the encoded streams, decodes the encoded streams to generate decoded video data, and multiplexes the ancillary data onto the decoded video data so that the input video data and decoded video data will have the same ancillary data. 
     A decoding apparatus for decoding the encoded streams generated by encoding input video data obtains the ancillary data contained in the picture area of the encoded streams, decodes the encoded streams to generate decoded video data, and multiplexes the decoded video data and ancillary data to generate the same data as the input video data. 
     A coding system comprises encoding means for encoding input video data and decoding means for receiving and decoding the encoded streams encoded by the encoding means to generate decoded video data; wherein the encoding means comprises means for encoding the above described input video data to generate encoded streams and means for inserting the ancillary data contained in the input video data into the encoded streams, and the decoding means comprises means for decoding the encoded streams to generate decoded video data and means for multiplexing the ancillary data transmitted with the encoded streams onto the decoded video data. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing the configuration of a system that comprises a conventional MPEG encoder and MPEG decoder. 
     FIG. 2 is a block diagram showing the configuration of an encoding system that comprises a 3:2 pull-down circuit. 
     FIG. 3 is a schematic diagram illustrating a 3:2 pull-down process. 
     FIG. 4 is a block diagram showing the configuration of the encoding/decoding system according to the present invention. 
     FIG. 5 is a schematic diagram showing an elementary stream and transport stream. 
     FIG. 6 is a block diagram showing the configuration of an MPEG encoder. 
     FIG. 7 is a schematic diagram illustrating a 3:2 pull-down process. 
     FIG. 8 is a schematic diagram showing the full pixel area and active video area of video data. 
     FIG. 9 is a schematic diagram showing the structure of each frame. 
     FIG. 10 is a schematic diagram showing the syntax of a video sequence. 
     FIG. 11 is a schematic diagram showing the syntax of a sequence header. 
     FIG. 12 is a schematic diagram showing the syntax of a sequence extension. 
     FIG. 13 is a schematic diagram showing the syntax of extension and user data. 
     FIG. 14 is a schematic diagram showing the syntax of user data. 
     FIG. 15 is a schematic diagram showing the syntax of a data ID. 
     FIG. 16 is a schematic diagram showing the syntax of V-Phase. 
     FIG. 17 is a schematic diagram showing the syntax of H-Phase. 
     FIG. 18 is a schematic diagram showing the syntax of a time code. 
     FIG. 19 is a schematic diagram showing the syntax of a time code. 
     FIG. 20 is a schematic diagram showing the syntax of a picture order. 
     FIG. 21 is a schematic diagram showing the syntax of ancillary data. 
     FIG. 22 is a schematic diagram showing the syntax of a group of picture header. 
     FIG. 23 is a schematic diagram showing the syntax of a picture header. 
     FIG. 24 is a schematic diagram showing the syntax of a picture coding extension. 
     FIG. 25 is a schematic diagram showing the syntax of picture data. 
     FIG. 26 is a schematic diagram showing the data of a sequence layer, GOP layer, and picture layer. 
     FIG. 27 is a block diagram showing the configuration of the multiplexing unit on the encoder side. 
     FIG. 28 is a schematic diagram illustrating the method of generating PES and TS packets from source video data. 
     FIG. 29 is a schematic diagram showing the data structure of a PES header. 
     FIG. 30 is a schematic diagram showing picture sequences. 
     FIG. 31 is a block diagram showing the configuration of an MPEG decoder. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     FIG. 4 shows a broadcasting system consisting of a main broadcasting station  141  and local broadcasting station  171 . 
     The main broadcasting station  141  comprises a plurality of editing/processing studios  145 A to  145 D, a plurality of MPEG encoders  142 A to  142 D, a plurality of MPEG decoders  144 A to  144 D, at least one multiplexer  162 A, and at least one demultiplexer  161 A. The broadcasting station  141  also includes an SDTI-CP (serial data transfer interface-content package) network  150  defined as SMPTE305M, through which each MPEG encoder, each MPEG decoder, the multiplexer  162 A, and the demultiplexer  161 A can send and receive elementary streams. SDTI-CP, which is a communications format proposed for transmission of elementary streams of MPEG, is defined as SMPTE305M. The elementary stream transferred over the SDTI-CP network  150  is expressed as ES_over_SDTI-CP. 
     The editing/processing studios  145 A to  145 D comprise video servers, video editors, special-effects devices, video switchers. They receive decoded base-band video data from the MPEG decoders, edit it or subject it to image processing, and output it to the MPEG encoders. In other words, editing/processing studios  145 A to  145 D perform editing and image-processing operations on base-band video signals rather than performing stream processing operations on encoded streams. 
     The MPEG encoders  142 A to  142 D receive base-band input video signals from the editing/processing studios  145 A to  145 D, and encode them according to the MPEG standard described above to generate elementary streams (ES). The elementary streams generated by the MPEG encoders are supplied to either of the MPEG decoders  144 A to  144 D or the multiplexer  162 A through the SDTI-CP network  150 . 
     The MPEG decoders  144 A to  144 D receive the elementary streams supplied by the MPEG encoders  142 A to  142 D or the demultiplexer  161 A through the SDTI-CP network  150 , and decode them according to the MPEG standard. The multiplexer  162 A is a circuit for multiplexing the plurality of video programs produced at the main broadcasting station  141  into one transport stream to distribute them to the local broadcasting station  171  or individual households. Specifically, it receives a plurality of elementary streams corresponding to the plurality of video programs through the SDTI-CP network  150 , generates packetized elementary streams by packetizing the elementary streams, and then generates transport stream packets from the packetized elementary streams. The multiplexer  162 A generates a multiplexed transport stream by multiplexing the transport stream packets generated from the plurality of video programs. The configuration and processes of the multiplexer  162 A will be described later. 
     If the destination of the plurality of video programs is the local broadcasting station  171 , the multiplexed transport stream generated by the multiplexer  162 A is supplied to the demultiplexer  161 B of the local broadcasting station  171  through a network such as an ATM (asynchronous transfer mode) network or satellite line. The local broadcasting station  171  has exactly the same system configuration as the main broadcasting station  141  although they differ in scale, and thus detailed description will be omitted. 
     If the destination of the plurality of video programs is the local broadcasting station  171 , the multiplexed transport stream generated by the multiplexer  162 A is supplied to the MPEG decoder  170 A contained in the set-top box at each household through a network such as an ATM (asynchronous transfer mode) network or satellite line, and decoded video data is supplied to the TV set. 
     FIG. 5 illustrates the differences between an elementary stream transmitted via an SDTI-CP network within a broadcasting station and a transport stream transferred via a public network. 
     Within the broadcasting station, the elementary stream is transmitted via an SDTI-CP network. The SDTI-CP network  150 , which uses a communications format based on the SDI (serial data interface) standardized by SMPTE259M and capable of a transfer rate of 270 Mbps, can transmit elementary streams (ES) in MPEG format directly and is suitable for closed networks such as studios. Specifically, video data “V” and audio data “A” are packed in each frame and the stream can be edited easily along the frame boundaries defined by a frame sync (dotted line) as shown in FIG.  5 A. 
     Between broadcasting stations or over public networks, video data is transmitted in the form of a transport stream. In a transport stream, all contents including video data and audio data are encapsulated into 188-byte packets, as shown in FIG. 5B, to allow data transmission even through a public network with a limited data-transmission capacity. As is the case with elementary streams, “V” indicates a transport stream packet of video data and “A” indicates a transport stream packet of audio data while a blank indicates a null packet. 
     Now the MPEG encoders  142 A to  142 D will be described with reference to FIG.  6 . First, a supplementary explanation will be given about the input video data supplied to the MPEG encoders. In this embodiment, the input video data is 30-Hz video data generated by 3:2 pull-down conversion from source video data having a frame rate of 24 Hz. Specifically, the original source video data with a frame rate of 24 Hz consists of the frames F 1 , F 2 , and so on, each of which has two fields (top field t 1 , t 2 , . . . and bottom field b 1 , b 2 , . . . ). As shown in FIG. 7A, the 3:2 pull-down process generates a repeat field t 1 ′ by repeating the top field t 1  in the first frame F 1 —where the top field should appear first—to form one frame from three fields, and generates a repeat field b 3 ′ by repeating the bottom field b 3  in the third frame F 3  where the bottom field should appear first. In this way, the 3:2 pull-down process can convert source video data with a frame rate of 24 Hz into video data with a frame rate of 30 Hz, as shown in FIG. 7A, by alternating 3-field frames and 2-field frames. 
     Although in this embodiment input video data is generated by 3:2 pull-down, the present invention is not limited to video data whose input video data has undergone 3:2 pull-down. It can also be applied to video data that has not undergone 3:2 pull-down, provided the original source video has a frame rate of 30 Hz. 
     The MPEG encoder shown in FIG. 6 comprises an ancillary data separating circuit  101 , a field counter  102 , a 2:3 pull-down circuit  103 , an encoding controller  104 , a motion vector detector  105 , a switching circuit  111 , a DCT circuit  112 , a quantizing circuit  113 , an inverse quantizing circuit  114 , an inverse DCT circuit  115 , an adding circuit  116 , memories  117  and  118 , a motion compensating circuit  119 , arithmetic circuits  120 ,  121 , and  122 , a variable-length coding circuit  125 , and a send buffer  126 . 
     The ancillary data separating circuit  101  extracts ancillary data from the blanking interval of input video data. More particularly, as shown in FIG. 8, it extracts the ancillary data inserted in the vertical blanking interval of input video data and the line number of the ancillary data. Such ancillary data includes, but is not limited to, text data, closed-captioning data, VITC (vertical interval time code) defined by SMPTE RP164, and LTC (linear time code) defined by RP196. In this embodiment, information about the extracted ancillary data is supplied to the controller  104  as Ancillary_data while information about the line number is supplied to the controller  104  as Line_number. Also, information about VITC is supplied to the controller  104  as Time_code_ 1  and information about LTC is supplied to the controller  104  as Time_code_ 2 . 
     Besides, the ancillary data separating circuit  101  extracts the unique information possessed by input video data. Such unique information may be, for example, data about the location of the active video area AR 2  with respect to the full pixel area AR 1  of input video data as shown in FIG.  8 . Specifically, it may include the number of lines that represents the vertical start position of the active video area and the number of samples that represents the horizontal start position. In this embodiment, the information about the vertical and horizontal positions of the active video area are supplied to the controller  104  as V-phase and H-phase, respectively. Other examples of the unique information includes the source name given to the input video data and the location and time of photo shooting. 
     The video data output from the ancillary data separating circuit  101  is supplied to the field counter  102  that follows. The field counter  102  is the circuit for counting the fields that compose each frame of the input video data. Then the field counter  102  supplies the count information of each frame to the controller  104  as Field_ID. If, for example, the video data shown in FIG. 7A is supplied to the field counter  102 , Field_ID of “0,” “1,” and “2” are output as the count information for frame F 1 , which has three fields, and Field_ID of “0” and “1” are output as the count information for frame F 2 , which has two fields. 
     The field counter  102  further comprises two counters that count the fields in the input video data and outputs the count information to the controller  104  as PTS_counter and DTS_counter. When generating an ES header, PTS_counter is used to generate presentation time stamps (PTSs) and DTS_counter is used to generate decoding time stamps (DTSs). 
     Now PTS_counter and DTS_counter will be described in detail with reference to FIG.  9 . FIG. 9 shows the frame structure of each frame in the input video data as well as the relationship between PTS_counter and DTS_counter in each frame. Before going into details on FIG. 9, a supplementary explanation will be given about the Repeat_first_field and Top_field_first flags. If the Repeat_first_field flag is set to “1”, it indicates that a repeat field must be created during MPEG decoding and if the Repeat_first_field flag is set to “0,” it indicates that a repeat field need not be created during MPEG decoding. The Top_field_first flag indicates whether the first field of the frame is the top field or bottom field: the value “1” indicates that the top field appears earlier than the bottom field in the frame while the value “0” indicates that the bottom field appears earlier than the top field in the frame. FIG. 9A illustrates the frame structure in the input video data described in FIG.  7 A. Specifically, the decoding of the first frame F 1  does not involve simply generating a frame consisting of a top field and bottom field, but it involves generating a frame consisting of three fields by creating a repeat field by copying the top field. Accordingly, the corresponding Repeat_first_field flag becomes “1” and the Top_field_first flag becomes “1.” 
     In decoding frame F 2 , the Repeat_first_field flag is set to “0” because there is no need to generate a repeat field, and the Top_field_first flag is set to “0” because the bottom field appears earlier than the top field. 
     In decoding frame F 3 , the bottom field must be copied to create a repeat field and the coded frame must be converted into a three-field frame. Therefore, the Repeat_first_field flag is set to “1” and the Top_field_first flag is set to “0.” In decoding frame F 4 , there is no need to create a repeat field, so the Repeat_first_field flag is set to “0” and the Top_field_first flag is set to 1. Since PTS_counter is the time stamp information underlying the PTS as described above, it must agree with the frame order of input video data. Specifically, PTS_counter is the value generated by a counter that increases from 0 to 127 and then returns to 0 again. The value of the counter PTS_counter changes in the manner shown in FIG.  9 B. More particularly, since the first frame F 1  in input video data is an I-picture and must be presented first, the value of PTS_counter is “0.” The value of PTS_counter for the second frame F 2  is the value “0” of PTS_for frame F 1  plus the number “3” of fields contained in frame F 1 , and thus is “3” (=0+3). The value of PTS_counter for the third frame F 3  is the value “3” of PTS_counter for frame F 2  plus the number “2” of fields contained in frame F 2 , and thus is “5” (=3+2). The value of PTS_counter for the fourth frame F 4  is the value “5” of PTS_counter for frame F 3  plus the number “3” of fields contained in frame F 3 , and thus is “8” (=5+3). The value of PTS_counter for the fifth frame F 5  and subsequent frames are calculated in a similar manner. Besides, since DTS_counter is the time stamp information underlying the DTS, it must agree with the order of pictures in encoded streams rather than with the frame order of input video data. Now this will be described in more concrete terms with reference to FIG.  9 C. Since the first frame F 1  is an I-picture, it must be decoded one frame earlier than it is displayed. In other words, since frame F 0  preceding the frame F 1  consists of two fields, the value of DTS_counter must be three fields ahead of the reference time “0,” i.e., it must be “125,” if the presentation time stamp PTS_counter=0 is used as the reference time. DTS_counter is given as a value modulo 27 (=128), and thus it cycles between 0 and 127. The value of DTS_counter for frame F 4  encoded after frame F 1  is equal to “0” (=128=125+3), which is given as the value “125” of DTS_counter for frame F 1  plus the number “3” of fields in frame F 1 . Since frame F 2  encoded next is a B-picture, the value of DTS_counter is equal to the value of PTS_counter, which is equal to “3.” Similarly, frame F 3  encoded next is a B-picture, and thus the value of DTS_counter is equal to the value of PTS_counter, which is equal to “5.” The values of DTS_counter for frame F 7  and subsequent frames are calculated similarly and the description thereof will be omitted herein. The field counter  102  generates PTS_counter and DTS_counter and supplies them to the controller  104  according to the rules described above. 
     The 2:3 pull-down circuit  103  receives the video data output from the field counter  102  and performs 2:3 pull-down. The 2:3 pull-down circuit  103  receives the video data with a frame rate of 30 Hz that has undergone 3:2 pull-down as shown in FIG.  7 A and generates video data with a frame rate of 24 Hz. More particularly, as shown in FIG. 7B, the 2:3 pull-down circuit  103  converts video data with a frame rate of 30 Hz into video data with a frame rate of 24 Hz by removing the repeat fields t 1 ′ and b 3 ′ inserted by 3:2 pull-down. In removing repeat fields, the 2:3 pull-down circuit  103  analyzes the frame structure of the supplied video data and removes only the repeat fields that are found to occur at certain intervals. Thus, when analyzing the frame structure of video data, the 2:3 pull-down circuit  103  generates Repeat_first_field and Top_field_first flags as information about the frame structure and supplies them to the controller  104 . 
     The motion vector detector  105  receives, in macroblocks, the video data output from the 2:3 pull-down circuit  103  and processes the image data in each frame as an I-picture, P-picture, or B-picture according to a predetermined sequence. The question as to how to process the image of each frame—as an I-picture, P-picture, or B-picture—has been predetermined according to the GOP structure specified by the operator. Any motion vector MV detected is supplied to the controller  104  and motion compensating circuit  119 . When the intra-picture prediction mode is activated, the switching circuit  111  closes the contact a. Therefore, the macroblock data is transmitted to the transmission path through the DCT circuit  112 , quantizing circuit  113 , variable-length coding circuit  125 , and send buffer  126 , as is the case with I-picture data. The quantized data is also supplied to the frame memory  117  for backward predictive pictures through the inverse quantizing circuit  114 , inverse DCT circuit  115 , and arithmetic unit  116 . On the other hand, when the forward prediction mode is activated, the switch  111  closes the contact b, the image data (the image data of the I-picture in this case) stored in the frame memory  118  for forward predictive pictures is read out, and compensation is made by the motion compensating circuit  119  based on the motion vector MV supplied by the motion vector detector  105 . In other words, when instructed to activate the forward prediction mode, the motion compensating circuit  119  reads data to generate predicted picture data, by offsetting the read address of the frame memory  118  for forward predictive pictures from the location that corresponds to the location of the macroblock currently output by the motion vector detector  105  by the amount equivalent to the motion vector. The predicted picture data output by the motion compensating circuit  119  is supplied to the arithmetic unit  120 . Then, from the data in the macroblock of the reference image, the arithmetic unit  120  subtracts the predicted picture data supplied by the motion compensating circuit  119  and corresponding to the macroblock, and outputs the difference (prediction error). This differential data is transmitted to the transmission path through the DCT circuit  112 , quantizing circuit  113 , variable-length coding circuit  125 , and send buffer  126 . Also, this differential data is decoded locally by the quantizing circuit  114  and inverse DCT circuit  115 , and is input to the arithmetic unit  116 . The arithmetic unit  116  has also been supplied with the same data as the predicted picture data supplied to the arithmetic unit  120 . The arithmetic unit  116  adds the predicted picture data output by the motion compensating circuit  119 , to the differential data output by the inverse DCT circuit  115 . This produces the image data of the original (decoded) P-picture. The image data of the P-picture is supplied to the backward predictive picture section of the frame memory  117 , where it is stored. After the data of the I-picture and P-picture is stored in the forward predictive picture section  118  and the backward predictive picture section  117 , respectively, the motion vector detector  105  processes the next picture, B-picture. In intra-picture prediction mode or forward prediction mode, the switch  111  closes the contacts a or b, respectively. The picture is processed in the same manner as P-pictures and the data is transmitted. On the other hand, when the backward prediction mode or bidirectional prediction mode is activated, switch  111  closes the contact c or d, respectively. In backward prediction mode with the contact c in the switch  111  closed, the image data (images of the P-picture in this case) stored in the backward predictive picture section  117  is read out and has its motion compensated by the motion compensating circuit  119  according to the motion picture output by the motion vector  105 . In other words, when the backward prediction mode is activated, the motion compensating circuit  119  reads data to generate predicted picture data, by offsetting the read address of the backward predictive picture section  117  from the location that corresponds to the location of the macroblock currently output by the motion vector detector  105  by the amount equivalent to the motion vector. The predicted picture data output by the motion compensating circuit  119  is supplied to the computing unit  121 . Then the computing unit  121  subtracts the predicted picture data supplied by the motion compensating circuit  119 , from the data in the macroblock of the reference image and outputs the difference. This differential data is transmitted to the transmission path through the DCT circuit  112 , quantizing circuit  113 , variable-length coding circuit  125 , and send buffer  126 . In bidirectional prediction mode with the contact d in the switch  111  closed, the image data (images of the I-picture in this case) stored in the forward predictive picture section  118  and image data (images of the P-picture in this case) stored in the backward predictive picture section  117  are read out and have their motions compensated by the motion compensating circuit  119  according to the motion picture output by the motion vector detector  105 . In other words, when the bidirectional prediction mode is activated, the motion compensating circuit  119  reads data to generate predicted picture data, by offsetting the read addresses of the forward predictive picture section  118  and backward predictive picture section  117  from the locations that correspond to the locations of the macroblock currently output by the motion vector detector  105  by the amount equivalent to the motion vectors (for both forward predictive picture and backward predictive picture, in this case). The predicted picture data output by the motion compensating circuit  119  is supplied to the computing unit  122 . Then the computing unit  122  subtracts the average of the predicted picture data supplied by the motion compensating circuit  119 , from the data in the macroblock of the reference image supplied by the motion vector detector  105  and outputs the difference. This differential data is transmitted to the transmission path through the DCT circuit  112 , quantizing circuit  113 , variable-length coding circuit  125 , and send buffer  126 . The images of B-pictures are not stored in the frame memories  117  and  118  because they are not used as predicted pictures for other pictures. The controller  104  controls all the circuits involved in the prediction mode processing, DCT mode processing, and quantization processing described above. Besides, the controller  104  supplies all the coding parameters, including motion vectors, picture types, prediction modes, DCT modes, quantizing steps, generated during the encoding of pictures to the variable-length coding circuit  125 . 
     Furthermore, the controller  104  receives V-phase, H-phase, Time_code 1 , Time_code 2 , Ancillary_data, and Line_number information from the ancillary data separating circuit  101  and receives DTS_counter, PTS_counter, and Field_ID information from the field counter  102 . Then it supplies the received V-phase, H-phase, Time_code 1 , Time_code 2 , Ancillary_data, Line_number, DTS_counter, PTS_counter, and Field_ID information to the variable-length coding circuit  125  as MPEG_ES_editing_information (i). 
     The variable-length coding circuit  125  converts the quantized DCT coefficient received from the quantizing circuit  113  and coding parameters received from the controller  104  into variable-length codes to generate an encoded stream according to the syntax of elementary streams specified by the MPEG standard. 
     A characteristic feature of this embodiment is that the variable-length coding circuit  125  also converts the information supplied from the controller  104  as MPEG_ES_editing_information (i) into variable-length codes and inserts them into the encoded stream. The syntax of encoded streams and the syntax of MPEG_ES_editing_information (i) will be described in detail later. 
     Now the syntax of bit streams will be described with reference to FIGS. 10 to  26 . Incidentally, FIG. 26 is an explanatory drawing illustrating the data structure of an MPEG encoded stream in an easy-to-understand form while FIGS. 10 to  25  describe the syntax in detail. FIG. 10 shows the syntax of a video stream of MPEG. The MPEG encoder  42  generates encoded elementary streams according to the syntax shown in FIG.  10 . In the descriptions of syntaxes that follow, functions and conditional statements are shown in lightface while data elements are shown in boldface. Data items are expressed in mnemonic form that represents their name, bit length, type, and transmission order. First the functions used in the syntax shown in FIG. 10 will be described. Actually, the syntax shown in FIG. 10 is used by the MPEG encoder  44  to extract meaningful data elements from the encoded bit stream received. The syntax used by the MPEG encoder  42  is the syntax obtained by omitting the conditional statements such as if and while statements from the syntax shown in FIG.  10 . 
     next_start_code( ) described first in video_sequence( ) is designed to search a bit stream for a start code. In any encoded stream generated according to the syntax shown in FIG. 10, the data element defined by sequence_header( ) and sequence_extension( ) are described first. The sequence_header( ) function is used to define header data for the sequence layer of an MPEG bit stream while the sequence_extension( ) function is used to define extension data for the sequence layer of the MPEG bit stream. The “do { } while” syntax placed next to the sequence_extension( ) function indicates that the data elements described based on the function in the braces { } of the do statement will remain in the encoded data stream while the condition defined by the while statement is true. The nextbits( ) function contained in the while statement is used to compare the bits or bit string described in the bit stream with the data elements referenced. In the example shown in FIG. 10, the nextbits( ) function compares the bit string in the bit stream with sequence_end_code that indicates the end of the video sequence, and if they do not match, the condition in the while statement holds true. Therefore, the “do { } while” syntax placed next to the sequence_extension( ) function indicates that the data elements defined by the function in the do statement will remain in the encoded bit stream until sequence_end_code that indicates the end of the video sequence is encountered. In the encoded bit stream, following the data elements defined by the sequence_extension( ) function, the data elements defined by extension_and_user_data( 0 ) have been described. The extension_and_user_data( 0 ) function is used to define extension data and user data for the sequence layer of an MPEG bit stream. The “do { } while” syntax placed next to extension_and_user_data( 0 ) indicates that the data elements described based on the function in the braces { } of the do statement will remain in the bit stream while the condition defined by the while statement is true. The nextbits( ) function contained in the while statement is used to determine the match between the bits or bit string in the bit stream and picture_start_code or group_start_code. If the bits or bit string in the bit stream and picture_start_code or group_start_code match, the condition defined by the while statement holds true. Therefore, the “do { } while” syntax indicates that if picture_start_code or group_start_code appears in the encoded bit stream, the data element codes defined by the function in the do statement are described next to the start code. The if statement described at the beginning of the do statement specifies the condition that group_start_code appears in the encoded bit stream. If the condition presented by the if statement is true, the data elements defined by group_of_picture_header( ) and extension_and_user_data( 1 ) are described in sequence next to group_start_code in the encoded bit stream. The group_of_picture_header( ) function is used to define header data for the GOP layer of an MPEG encoded bit stream while the extension_and_user_data( 1 ) function is used to define extension data and user data for the GOP layer of the MPEG encoded bit stream. Besides, in this encoded bit stream, next to the data elements defined by group_of_picture_header( ) and extension_and_user_data( 1 ), data elements defined by picture header( ) and picture_coding_extension( ) have been described. Of course, if the condition of the if statement described above does not hold true, the data elements defined by group_of_picture_header( ) and extension_and_user_data( 1 ) are not described, and thus next to the data elements defined by extension_and_user_data( 0 ), the data elements defined by picture_header( ), picture_coding_extension( ) and extension_and_user_data( 2 ) are described. The picture_header( ) function is used to define header data for the picture layer of an MPEG encoded bit stream while the picture_coding_extension( ) function is used to define first extension data for the picture layer of the MPEG encoded bit stream. The extension_and_user_data( 2 ) function is used to define extension data and user data for the picture layer of the MPEG encoded bit stream. The user data defined by extension_and_user_data( 2 ) has been defined in the picture layer and can be defined for each picture. In the encoded bit stream, next to the user data in the picture layer, the data elements defined by picture_data( ) have been described. The picture_data( ) function is used to describe data elements associated with a slice layer and macroblock layer. The while statement described next to the picture_data( ) function is the function used to judge the condition of the next if statement while the condition defined by the while statement is true. The nextbits( ) function contained in the while statement is used to determine whether picture_start_code or group_start_code has been described in the encoded bit stream. If picture_start_code or group_start_code has been described in the encoded bit stream, the condition defined by the while statement holds true. The if statement that appears next is the conditional statement used to determine whether sequence_end_code has been described in the encoded bit stream. It indicates that if sequence_end_code has not been described, the data elements defined by sequence_header( ) and sequence_extension( ) have been described. Since sequence_end_code is the code that indicates the end of the sequence of an encoded video stream, the data elements defined by sequence_header( ) and sequence_extension( ) should remain in the encoded video stream unless the encoded video stream has ended. The data elements described here by sequence_header( ) and sequence_extension( ) are exactly the same as the data elements described by sequence_header( ) and sequence_extension( ) at the beginning of the sequence of the video stream. In this way, the same data is described in a stream more than once to avoid cases in which it will become impossible to receive sequence layer data and decode the stream when the data stream is received from the middle (e.g., the part of the bit stream that corresponds to the picture layer) by the bit stream receiver. After the data elements defined by the last sequence_header( ) and sequence_extension( ), i.e., at the end of the data stream, two-bit sequence_end_code is described indicating the end of the sequence. Now detailed description will be given of sequence_header( ), sequence_extension( ), extension_and_user_data( 0 ), group_of_picture_header( ), picture_header( ), picture_coding_extension( ), and picture_data. FIG. 11 illustrates the syntax of sequence_header( ). The data elements defined by sequence_header( ) include sequence_header_code, horizontal_size_value, vertical_size_value, aspect_ratio_information, frame_rate_code, bit_rate_value, marker_bit, vbv_buffer_size_value, constrained_parameter_flag, load_intra_quantizer_matrix, intra_quantizer_matrix[ 64 ], load_non_intra_quantizer_matrix, non_intra_quantizer_matrix, etc. sequence_header_code is the data that represents the start synchronization code of the sequence layer. horizontal_size_value is the data that consists of the low-order 12 bits of the horizontal pixel count of an image. vertical_size_value is the data that consists of the low-order 12 bits of the vertical line count of an image. aspect_ratio_information is the data that represents the aspect ratio of a pixel or a display screen. frame_rate_code is the data that represents the display cycle of an image. bit_rate_value is the data that consists of the low-order 18 bits (rounded up to the nearest multiple of 400 bps) of the bit rate used to limit the amount of bits generated. marker_bit is the bit data that is inserted to avoid start code emulation. vbv_buffer_size_value represents the low-order 10 bits of the value that determines the size of the virtual buffer (video buffer verifier) for controlling the amount of codes generated. constrained_parameter_flag is the data which indicates that parameters fall within limits. load_intra_quantizer_matrix is the data that indicates the existence of quantization matrix data for intra MB. intra_quantizer_matrix[ 64 ] is the data that represents the value of the quantization matrix for intra MB. load_non_intra_quantizer_matrix is the data that indicates the existence of quantization matrix data for non-intra MB. non_intra_quantizer_matrix is the data that represents the value of the quantization matrix for non-intra MB. FIG. 12 illustrates the syntax of sequence_extension( ). The data elements defined by sequence_extension( ) include extension_start_code, extension_start_code_identifier, profile_and_level_indication, progressive_sequence, chroma_format, horizontal_size_extension, vertical_size_extension, bit_rate_extension, vbv_buffer_size_extension, low_delay, frame_rate_extension_n, frame_rate_extension_d, etc. 
     extension_start_code is the data that represents the start synchronization code of extension data. extension_start_code_identifier is the data that indicates which extension data will be sent. profile_and_level_indication is the data used to specify the profile and level of video data. progressive_sequence is the data which indicates that video data is to be scanned sequentially. chroma_format is the data used to specify the color difference format of video data. horizontal_size_extension represents the high-order 2 bits of the data to be added to horizontal_size_value in the sequence header. vertical_size_extension represents the high-order 2 bits of the data to be added to vertical_size_value in the sequence header. bit_rate_extension represents the high-order 12 bits of the data to be added to bit_rate_value in the sequence header. vbv_buffer_size_extension represents the high-order 8 bits of the data to be added to vbv_buffer_size_value in the sequence header. low_delay is the data which indicates that no B-picture is included. frame_rate_extension_n is used in conjunction with frame_rate_code in the sequence header to obtain the frame rate. frame_rate_extension_d is used in conjunction with frame_rate_code in the sequence header to obtain the frame rate. FIG. 13 illustrates the syntax of extension_and_user_data(i). When “i” is other than 1, extension_and_user_data(i) describes only the data elements defined by user_data( ), and not the data elements defined by extension_data( ). Therefore, extension_and_user_data( 0 ) describes only the data elements defined by user_data( ). First, the functions used by the syntax shown in FIG. 13 will be described. The nextbits( ) function is used to compare the bits or bit string in the bit stream with the data element to be decoded next. user_data( ) in FIG. 14 illustrates the characteristic features of this embodiment. As shown in FIG. 14, the user_data( ) function is used to describe the data elements associated with user_data_start_code, V-phase( ), H-phase( ), Time_code( ), Picture_order( ), Ancillary_data( ), history_data( ), and user_data( ). user_data_start_code is the start code used to indicate the start of the user data area in the picture layer of an MPEG bit stream. The if statement described next to this code specifies to run the while syntax that follows if i in user_data(i) is “0.” The while syntax remains true unless 24-bit data consisting of twenty-three “0&#39;s” and accompanying “1” appears in the bit stream. The 24-bit data consisting of twenty-three “0&#39;s” and accompanying “1” is added to the beginning of all start codes, allowing the nextbits( ) function to find the location of each of the start codes in the bit stream. If the while statement is true, it follows that i in user_data(i) is “0,” and thus there should be extension_and_user_data( 0 ) in the sequence layer. This means that in the sequence layer in FIG. 26, data elements associated with extension_and_user_data( 0 )  205  have been described. If a bit string (Data_ID) representing V-Phase is detected, the nextbits( ) function in the next if statement knows that the subsequent bits describe the V-Phase data elements indicated by V-Phase( ). If a bit string (Data_ID) representing H-Phase is detected, the nextbits( ) function in the next Else if statement knows that the subsequent bits describe the H-Phase data elements indicated by H-Phase( ). 
     This means that the data elements associated with V-Phase( )  220  and H-Phase( )  221  have been described in the user data area of the sequence layer as shown in FIG.  26 . As shown in FIG. 15, Data_ID of V-Phase is a bit string representing “01.” Data_ID of H-Phase is a bit string representing “02.” Now the syntax of V-Phase( ) described in the bit stream will be explained with reference to FIG.  16 . As described above, Data_ID is the 8-bit data which indicates that the data elements of the next bit string is V-Phase, i.e., the value “01” shown in FIG.  15 . V-Phase is the 16-bit data that indicates the first line to be encoded in a video signal frame. In other words, V-Phase is the data that indicates the vertical line number of the active video area. 
     Now the syntax of H-Phase( ) described in the bit stream will be explained with reference to FIG.  17 . As described above, Data_ID is the 8-bit data which indicates that the data elements of the next bit string is H-Phase, i.e., the value “02” shown in FIG.  15 . H-Phase is the 8-bit data that indicates the first sample to be encoded in a video signal frame. In other words, H-Phase is the data that indicates the horizontal pixel sample position of the active video area. 
     Returning to FIG. 14, the next Else if statement executes the next while syntax if i in extension_and_user_data(i) is 2. Description of the while syntax will be omitted because it has the same meaning as the while syntaxes described above. When the while syntax is true, if a bit string indicating Time code 1  or Time code 2  is detected, the nextbits( ) function in the next if statement knows that the subsequent bits describe the time code data elements indicated by Time_code( ). This means that if i in extension_and_user_data(i) is 2, this user data is contained in the picture layer. That is, the data elements represented by Time_code( )  241  have been described in the user data area of the picture layer as shown in FIG.  26 . 
     Data_ID of Time code 1  is a bit string representing “03” as shown in FIG.  15 . Time code 1  data is the VITC (vertical interval time code) that represents the time code inserted in the vertical blanking interval of an image. Data_ID of Time code 2  is a bit string representing “04” as shown in FIG.  15 . Time code 2  data is the LTC (longitudinal time code or linear time code) that represents the time code recorded on the time code track of the recording medium. 
     FIGS. 18 and 19 show the syntax of Time_code( ). As shown in FIG. 18, the time code consists of 72-bit data. FIG. 19 shows the concrete data structure. 
     In FIG. 19, color_frame_flag represents the control flag of color frame information while Drop_frame_flag that follows represents the control flag of dropped frames. The six bits from the third bit to the eighth bit represent the ‘frame’ section of the time code: field_phase represents the control flag of phase correction. The seven bits from the 10th bit to the 16th bit represent the ‘seconds’ section of the time code. The ‘1’ in the 17th, 34th, 51st, and 68th bits is a marker bit used to prevent 0 from occurring 23 times successively. The insertion of the marker bit at certain intervals can prevent start code emulation. 
     binary_group in the 18th, 26th, and 27th bits represents a control flag for binary groups. The seven bits from the 19th bit to the 25th bit represent the ‘minutes’ section of the time code while the six bits from the 28th bit to the 33rd bit represent the ‘hours’ section of the time code. In FIG. 14, if a bit string indicating a picture order is detected, the nextbits( ) function in the Else if statement knows that the subsequent bits describe the picture order data elements indicated by Picture_Order( ). Data_ID of Picture_Order( ) is a bit string representing “05” as shown in FIG.  15 . Now the syntax of Picture_Order( ) inserted actually into the elementary stream (ES) by the encoder will be described with reference to FIG.  20 . As described above, Data_ID is the 8-bit data which indicates that the subsequent data is the Picture_Order data and its value is “05.” DTS_presence is the 1-bit data that indicates the presence or absence of the coding order DTS_counter. For example, if DTS_counter=PTS_as in the case of B-pictures, only the presentation order PTS_counter exists and the bit of DTS_presence becomes “0.” Conversely, in case of P-pictures and I-pictures, the coding order DTS_counter and presentation order PTS_counter are not equal, so both coding order DTS_counter and presentation order PTS_counter exist and the bit of DTS_presence becomes 1. As described in FIG. 26, the data elements associated with Picture_Order( ) are described in the user data area of the picture layer as is the case with Time_Code( ). As described above, PTS_counter is the value generated by the field counter  102  in the MPEG encoder. It is the 7-bit data which represents the presentation order and which is incremented by 1 each time one field of the input video data is filled. This 7-bit data is given as the remainder of modulo division and takes on values from 0 to 127. The if statement indicates that DTS_counter is incremented if the bit of DTS_presence is 1, i.e., in the case of a P-picture and I-picture. Marker_bits is inserted every 16 bits to prevent start code emulation, a phenomenon in which a described bit string of user data accidentally matches the start code described above leading to a high possibility of image corruption. DTS_counter is the value generated by the field counter  102  in the MPEG encoder. It is the 7-bit data which represents the coding order and which is incremented by 1 each time one field of the input video data is encoded. This 7-bit data is given as the remainder of modulo division and takes on values from 0 to 127. Returning to FIG. 14, the while syntax has the same meaning as the while syntaxes described above, and thus description thereof will be omitted. When the while syntax is true, if a bit string indicating ancillary data is detected, the nextbits( ) function in the next if statement knows that the subsequent bits describe the ancillary data elements indicated by Ancillary_data( ). Data_ID of Ancillary_data( ) is a bit string representing “07” as shown in FIG.  15 . As shown in FIG. 26, the data elements associated with Ancillary_data( ) have been described in the user data area of the picture layer as is the case with Picture_Order( ) and Time_Code( ). Now the syntax of Ancillary_data( ) that adds identifiers to ancillary data will be described with reference to FIG.  21 . Ancillary_data( ), which is inserted as user data in the picture layer, includes a field identifier (Field_ID), a line number (Line_number), and ancillary data. Data_ID is 8-bit data which is an ancillary data in the user data area, having a value of “07” as shown in FIG.  15 . Field_ID is the 2-bit data that is added to each field in coded frames when the value of progressive_sequence_flag, which indicates whether the input video data is progressive video, is “0,” i.e., when the input video data is interlaced video data. 
     Now Field_ID will be described with reference to FIG.  7 . 
     If repeat_first_field contains “0,” the given frame has two fields: Field_ID of the first field is set to “0” and Field_ID of the second field is set to “1.” If repeat_first_field contains “1,” the given frame has three fields: Field_ID of the first, second, and third fields is set to “0,” “1,” and “2,” respectively. Now more detailed description will be provided with reference to FIG.  7 C. The encoded stream shown in FIG. 7C is obtained when the input video data shown in FIG. 7B is encoded. This encoded stream is an elementary stream consisting of a plurality of access units (AU 1 , AU 2 , . . . ). FIG. 7C shows the ancillary data and Field_ID information described in the elementary stream. 
     Frame F 1  of this encoded stream contains 0, 1, and 2 as Field_ID. In other words, when Field_ID=0, ancillary data “0” about that field is described in the stream, when Field_ID=1, ancillary data “1” about that field is described in the stream, and when Field_ID=2, ancillary data “2” about that field is described in the stream. This means that in the picture of frame F 1 , the data elements associated with Ancillary_data( )  243  are repeated as many times as the number of the fields in frame F 1 , as shown in FIG.  26 . 
     Field_ID is added for each coded frame when the value of progressive_sequence_flag, is “1,” i.e., when the input video data is 1. If both repeat_first_field and Top_field_first contain Field_ID of “0,” the given coded frame has one progressive frame and thus “0” is set. If repeat_first_field contains “1” and Top_field_first contains “0,” the given coded frame has two progressive frames and thus “0” and “1” are set. If both repeat_first_field and Top_field_first contain “1,” the given coded frame has three progressive frames and thus “0” to “2” is set. Line_number is 14-bit data which represents the line number of the line where the ancillary data of each frame is described. This line number has been specified by ITU-R, BT.656-3, SMPTE274M, SMPTE293M, and SMPTE296M. Ancillary_data_length is the 16-bit data which represents the data length of ancillary_data_payload. Ancillary_data_payload represents the content of 22-bit ancillary data. If the value of Ancillary_data_length for Ancillary_data_payload is larger than the value j (default of 0), the value j (data length of Ancillary_data_length) is incremented by 1 and description starts from the bit string of the value j. The While syntax that follows shows the syntax of bytealigned( ). It describes Zero_bit (1-bit data “0”) when the next data is not bytealigned( ) (when the While syntax is true). Returning to FIG. 14, if a bit string indicating history data is detected, the nextbits( ) function in the next Else if statement knows that the subsequent bits describe the data elements of history data indicated by History_data( ). Data_ID of History_data( ) is a bit string representing “08” as shown in FIG.  15 . The data represented by Data_ID of “08” represents history data that includes the history information of coding parameters. History_data( ) is described in detail in U.S. patent application Ser. No. 09/265,723, and thus description thereof is omitted herein. If a bit string indicating user data is detected, the nextbits( ) function in the final if statement knows that the subsequent bits describe the user_data data elements indicated by user_data( ). The bit strings from which the nextbits( ) functions in FIG. 14 know that the subsequent bits describe appropriate data elements are described as Data_ID shown in FIG.  15 . However, the use of “00” as Data_ID is prohibited. The data represented by Data_ID of “80” represents a control flag while the data represented by Data_ID of “FF” represents user data. FIG. 22 illustrates the syntax of group_of_picture_header( ). The data element defined by group_of_picture_header( ) consists of group_start_code, time_code, closed_gop, and broken_link. group_start_code is the data that represents the start synchronization code of the GOP layer. time_code represents the time from the beginning of the sequence of the first picture in the GOP. closed_gop is the flag which indicates that the images in the GOP can be played back independent of other GOPs. broken_link is the flag which indicates that the B-picture at the beginning of GOP cannot be played back correctly due to editing. 
     The extension_and_user_data( 1 ) function is used to describe only the data elements defined by user_data( ), as is the case with extension_and_user_data( 0 ). Now, with reference to FIGS. 23 to  25 , description will be given of picture_header( ), picture_coding_extension( ), and picture_data( ) used to describe data elements associated with the picture layer of encoded streams. FIG. 23 illustrates the syntax of picture_header( ). The data elements defined by picture_header( ) include picture_start_code, temporal_reference, picture_coding_type, vbv_delay, full_pel_forward_vector, forward_f_code, full_pel_backward_vector, backward_f_code, extra_bit_picture, and extra_information_picture. Specifically, picture_start_code is the data that represents the start synchronization code of the picture layer. temporal_reference is the number that indicates the presentation order of pictures and is reset at the beginning of a GOP. picture_coding_type is the data that represents a picture type. vbv_delay is the data that represents the initial state of a VBV buffer and is set for each picture. The pictures in the encoded elementary stream transmitted from the sending system to the receiving system is placed in the VBV buffer provided in the receiving system, fetched (read out) from this VBV buffer at the time specified by the DTS (decoding time stamp), and supplied to the decoder. The time defined by vbv_delay is the period from the moment the picture to be decoded is started to be placed in the VBV buffer until the picture to be encoded is read out from the VBV buffer, i.e., until the time defined by the DTS. The use of vbv_delay stored in the picture header allows seamless splicing avoiding discontinuity in the occupancy of the VBV buffer. full_pel_forward_vector is the data that indicates whether the accuracy of forward motion vectors should be expressed in integers or half-pixels. forward_f_code is the data that indicates the search range of forward motion vectors. full_pel_backward_vector is the data that indicates whether the accuracy of backward motion vectors should be expressed in integers or half-pixels. backward_f_code is the data that indicates the search range of backward motion vectors. extra_bit_picture is the flag that indicates the existence of subsequent additional information. If extra_bit_picture is “1,” extra_information_picture follows. If extra_bit_picture is “0”, no subsequent data exists. extra_information_picture is the information reserved by the standard. FIG. 24 illustrates the syntax of picture_coding_extension( ). The data elements defined by picture_coding_extension( ) include extension_start_code, extension_start_code_identifier, f_code[ 0 ] [ 0 ], f_code[ 0 ] [ 1 ], f_code[ 1 ] [ 0 ], f_code[ 1 ] [ 1 ], intra_dc_precision, picture_structure, top_field_first, frame_predictive_frame_dct, concealment_motion_vectors, q_scale_type, intra_vlc_format, alternate_scan, repeat_first_field, chroma_ 420 _type, progressive_frame, composite_display_flag, v_axis, field_sequence, sub_carrier, burst_amplitude, and sub_carrier_phase 
     extension_start_code indicates the start of extension data in the picture layer. extension_start_code_identifier is the code that indicates what extension data is sent. f_code[ 0 ] [ 0 ] is the data that indicates the search range of forward horizontal motion vectors. f_code[ 0 ] [ 1 ] is the data that indicates the search range of forward vertical motion vectors. f_code[ 1 ] [ 0 ] is the data that indicates the search range of backward horizontal motion vectors. f_code[ 1 ] [ 1 ] is the data that indicates the search range of backward vertical motion vectors. intra_dc_precision is the data that represents the accuracy of the DC coefficient. picture_structure is the data that indicates whether the picture has a frame structure or field structure. In the case of the field structure, it also indicates whether the field is an upper field or lower field. top_field_first is the flag that indicates whether the first field is the top field or bottom field in the case of the frame structure. frame_predictive_frame_dct is the data which indicates that the frame mode DCT prediction is only in the frame mode in the case of the frame structure. concealment_motion_vectors is the data which indicates that intra-macroblocks are provided with motion vectors for hiding transmission errors. q_scale_type is the data that indicates which quantization scale to use, linear or non-linear. intra_vlc_format is the data that indicates whether to use another two-dimensional VLC (variable-length code) for intra-macroblocks. alternate_scan is the data that indicates which scan to use, zigzag scan or alternate scan. repeat_first_field is the flag that indicates whether to generate a repeat field during decoding. If this flag is set to “1”, a repeat field is generated during decoding. If this flag is set to “0,” no repeat field is generated during decoding. chroma_ 420 _type is the data that indicates the same value as progressive_frame if the signal format is 4:2:0, and indicates 0 otherwise. progressive_frame is the data that indicates whether the picture can be scanned progressively. composite_display_flag is the data that indicates whether the source signal was a composite signal. v_axis is data used when the source signal is a PAL signal. field_sequence is data used when the source signal is a PAL signal. sub_carrier is data used when the source signal is a PAL signal. burst_amplitude is data used when the source signal is a PAL signal. sub_carrier_phase is data used when the source signal is a PAL signal. FIG. 25 illustrates the syntax of picture_data( ). The data elements defined by picture_data( ) is the data elements defined by slice( ). However, if slice_start_code that indicates the start code of slice( ) does not exist in the bit stream, the data elements defined by slice( ) have not been described in the bit stream. 
     The slice( ) function is used to describe the data elements associated with a slice layer. Specifically, it is used to describe data elements such as slice_start_code, slice_quantiser_scale_code, intra_slice_flag, intra_slice, reserved_bits, extra_bit_slice, and extra_information_slice as well as the data elements defined by macroblock ( ). 
     slice_start_code indicates the start of the data elements defined by slice( ). slice_quantiser_scale_code is the data that indicates the size of the quantizing step specified for the macroblocks in the slice layer. If quantiser_scale_code has been specified for each macroblock, however, the macroblock_quantiser_scale_code takes precedence. intra_slice_flag indicates the presence or absence of intra_slice and reserved_bits in the bit stream. intra_slice is the data that indicates the presence or absence of a non-intra macroblock in the slice layer. If any of the macroblocks in the slice layer is a non-intra macroblock, intra_slice is set to “0.” If all the macroblocks in the slice layer are non-intra macroblocks, intra_slice is set to “1.” reserved_bits is 7-bit data which takes on the value of “0.” extra_bit_slice is the flag that indicates the presence of additional information as an encoded stream. It is set to “1” if extra_information_slice follows. It is set to “0” if no additional information exists. The macroblock ( ) function is used to describe the data elements associated with a macroblock layer. Specifically, it is used to describe data elements such as macroblock_escape, macroblock_address_increment, and macroblock_quantiser_scale_code as well as the data elements defined by macroblock_modes( ) and macroblock_vectors(s). macroblock_escape is the fixed bit string that indicates whether the horizontal difference between the reference macroblock and previous macroblock is equal to or more than 34. If the horizontal difference is 34 or larger, 33 is added to the value of macroblock_address_increment. macroblock_address_increment is the data that represents the horizontal difference between the reference macroblock and previous macroblock. If macroblock_address_increment is preceded by one macroblock_escape string, the actual horizontal difference between the reference macroblock and previous macroblock is the value of macroblock_address increment plus 33. macroblock_quantiser_scale_code represents the size of the quantization step specified for each macroblock. Although slice_quantiser_scale_code has been specified for each slice layer to indicate the quantization step size of the slice layer, the quantization step size of the reference macroblock is selected if macroblock_quantiser_scale_code has been specified for the reference macroblock. 
     Now the multiplexer  162 A will be described with reference to FIG.  27 . 
     The multiplexer  162 A comprises a plurality of packetizers  301  to  309 , a plurality of transport stream generators (TS Gen.)  311  to  319 , a plurality of system target decoder buffers (STD buffers)  321  to  329 , a multiplexing circuit  330 , and a multiplexing controller  300 . 
     The packetizers  301  to  309  receive the respective elementary streams output by MPEG encoders and packetize the elementary streams to generate packetized elementary streams (PES). 
     FIG. 28 illustrates the relationship among an elementary stream (ES), a packetized elementary stream (PES), and transport stream packets. 
     When source video data is encoded, an elementary stream, such as the one shown in FIG. 28B, consisting of access units AU 1 , AU 2 , . . .is generated. FIG. 28C illustrates packetization performed by a packetizer. The packetizer packetizes a plurality of access units and adds a PES header to the beginning of the packet. 
     FIG. 29 illustrates the PES header. As shown in the figure, the PES header consists of Packet Start Code, Stream ID, Packet Length, symbol “10,” Flag Control Code, PES Header Length, and Conditional Coding. The MPEG standard stipulates that the conditional coding must contain presentation time stamp (PTS) and decoding time stamp (DTS) information. Each of the transport stream generators (TS Gen.)  311  to  319  generate a transport stream consisting of 188-byte transport stream packets from the packetized elementary streams output by the packetizers  301  to  309 , as shown in FIG.  28 D. 
     The system target decoder buffers (STD buffers)  321  to  329  receive the transport streams output by the transport stream generators  311  to  319  and buffer them. The STD buffers are fixed-capacity buffers specified by the MPEG standard and are provided for the purpose of simulation to prevent receive buffer from overflowing and underflowing on the MPEG decoder side. The multiplexing circuit  330  receives a transport stream from each of the system target decoder buffers  321  to  329  and multiplexes the transport streams according to the schedule set by the controller  300 . 
     Next, the configuration and processes of the packetizers will be described in detail with reference to FIGS. 27 and 30. 
     Each of the packetizer comprises a buffer  341  for buffering the elementary streams received, a parsing circuit  342  for parsing the syntax of the elementary streams received, and packetizing circuit  343  for packetizing the elementary streams output from the buffer. 
     The parsing circuit  342  extracts PTS_counter and DTS_counter described in the elementary stream and supplies them to the packetizing circuit  343 . More particularly, the parsing circuit  342  converts the received elementary stream into variable-length codes and searches the elementary stream for start codes and other special data elements. Since the purpose of this parsing process is to extract PTS_counter and DTS_counter, the parsing process searches for the start code of the picture layer, ignoring the start code of the sequence and GOP layers. Next, the parsing process can find out the user data area of the picture layer by finding out 32-bit user_data_start_code from the stream. Then it searches for Data_ID of “05” to find out data elements associated with Picture_order( ) in this user data-area. The parsing circuit  342  extracts PTS_counter and DTS_counter described in the 10th to 16th bits and 17th to 23rd bits of this Picture_order( ) function, respectively, and supplies them to the packetizing circuit  343 . The packetizing circuit  343  receives PTS_counter and DTS_counter from the parsing circuit  342  and based on this PTS_and DTS_counter information, generates PTS and DTS anew. This embodiment uses the value of PTS_counter itself as the PTS value and uses the value of DTS_counter as the DTS value. 
     FIG. 30 illustrates the minimum delay produced when the packetizer of this embodiment is used. FIG. 30A shows input video data, FIG. 30B shows the elementary stream obtained when the input video data is encoded, and FIG. 30C shows the packetized elementary stream obtained by using the encoded stream generated by the MPEG encoder of this embodiment and packetizer of this embodiment. FIGS. 30A and 30B are almost the same as FIGS. 2A and 2B. However, as can be seen by comparing FIG.  2 C and FIG. 30C, conventional methods generate a packetized elementary stream that determines PTS. Thus, as described earlier, if the number of B-pictures existing between an I-picture and P-pictures is denoted as N, there is a delay of (N+2) frames in the PTS determination process. 
     The encoding method and packetizing method of this embodiment can limit the delay produced in the process of determining PTS from an encoded stream, to one frame time. Furthermore, regardless of the number of B-pictures existing between an I-picture and P-pictures, the delay can be kept to the minimum delay of one frame. Besides, when designing a 9-channel packetizer such as the one shown in FIG. 27, this embodiment has an extremely great advantage of allowing to implement such a packetizer with nine frame memories. 
     Now the MPEG decoders  144 A to  144 D will be described with reference to FIG.  31 . Each of the MPEG decoders comprises a receive buffer  401 , a variable-length decoding circuit  402 , an inverse quantizing circuit  403 , an inverse DCT circuit  404 , a controller  405 , an arithmetic unit  411 , a motion compensating circuit  412 , memories  413  and  414 , a send buffer  415 , a base-band video generation circuit  416 , and a multiplexing circuit  417 . 
     The variable-length decoding circuit  402  receives an elementary stream from the receive buffer and performs a variable-length decoding operation on it to generate a stream consisting of data elements with a predetermined data length. Then, the variable-length decoding circuit  402  parses the syntax of the data stream that has been subjected to variable-length decoding, thereby extracting all coding parameters from the data stream, and supplies them to the controller  405 . Examples of the coding parameters that are required by the MPEG standard to be superimposed in the stream include picture type, motion vector, prediction mode, DCT mode, quantization scale code, quantization table information, etc. Basically, they are the parameters produced during the encoding process for generating the encoded stream. 
     A unique feature of this embodiment is that the variable-length decoding circuit  402  extracts the information described as MPEG_ES_Editing_information( ) in the user data area of elementary streams in addition to the coding parameters specified by the MPEG standard as described above. Specifically, information about V-phase( ) and H-phase( ) is described as MPEG_ES_Editing_information( ) in the user data area in the sequence layer of encoded streams, and information about Time_code( ), Picture_order( ), Ancillary_data( ), and History_data( ) is described as MPEG_ES_Editing_information( ) in the user data area in the picture layer of encoded streams. The variable-length encoding circuit  402  extracts the information about V-phase( ), H-phase( ), Time_code( ), Picture_order( ), Ancillary_data( ), and History_data( ) from the streams and supplies it to the controller  405 . 
     The inverse quantizing circuit  403  inverse-quantizes the DCT coefficient data supplied by the variable-length decoding circuit  402  after variable-length decoding, based on the quantization scale supplied also by the variable-length decoding circuit  402  and supplies it to the inverse DCT circuit  404 . 
     The inverse DCT circuit  404  performs an inverse DCT (discrete cosine transform) process on the quantized DCT coefficient supplied by the inverse quantizing circuit  403  and supplies it as image data subjected to inverse DCT to the arithmetic unit  411 . If the image data supplied to the arithmetic unit  411  by the inverse DCT circuit  404  is an I-picture, it is output from the arithmetic unit  411 , supplied to the forward predictive picture section of the frame memory  414 , and stored there for use to generate predictive picture data of the image data (P-picture or B-picture data) to be input later into the arithmetic unit  411 . If the image data supplied by the inverse DCT circuit  404  is P-picture data that uses the image data of the immediately preceding frame as predictive picture data and if it is data in forward prediction mode, the image data (I-picture data) of the immediately preceding frame is read out from the forward predictive picture section of the frame memory  414  and subjected to motion compensation in the motion compensating circuit  412  corresponding to the motion vector output from the variable-length decoding circuit  402 . Then the P-picture data is output after the image data (differential data) supplied by the inverse DCT circuit  404  is added to it in the arithmetic unit  411 . The sum data, i.e., the decoded P-picture is supplied to the backward predictive picture section of the frame memory  413 , and stored there for use to generate predictive picture data of the image data (B-picture or P-picture data) to be input later into the arithmetic unit  411 . Intra-picture prediction mode data is not processed in the arithmetic unit  411  and stored as it is in the backward predictive picture section  413  as is the case with I-picture data even if it is P-picture data. Since this P-picture is to be displayed after the B-picture that follows, it is not output to a format conversion circuit  32  at this time (as described above, the P-picture input later than the B-picture is processed and transmitted before the B-picture). If the image data supplied by the inverse DCT circuit  404  is B-picture data, the image data of the I-picture stored in the forward predictive picture section of the frame memory  414  (in the case of forward prediction mode), image data of the P-picture stored in the backward predictive picture section  413  (in the case of backward prediction mode), or both image data (in the case of bidirectional backward prediction mode) are read out according to the prediction mode supplied from the variable-length decoding circuit  402 . The image data is then subjected to motion compensation in the motion compensating circuit  412  according to the motion vector output from the variable-length decoding circuit  402 , to generate a predictive picture. However, no predictive picture is generated if no motion compensation is necessary (in the case of intra-picture prediction mode). The data that has thus been subjected to motion compensation by the motion compensating circuit  412  has the output from the inverse DCT circuit  404  added to it in the arithmetic unit  411 . The sum output is supplied to the base-band video generation circuit  416  via the buffer  415 . The video data output from this send buffer  415  contains only the video data for the active video area, but is not provided with ancillary data for the blanking interval or the like. 
     The controller  405  controls the operation of the circuits described above, based on the information about picture type, motion vector, prediction mode, DCT mode, quantization scale, quantization table information, and other coding parameters supplied by the variable-length decoding circuit  402 . 
     Furthermore, the controller  405  controls the base-band video generation circuit  416 , based on the V-phase and H-phase information supplied from the variable-length decoding circuit  402  as MPEG_ES_Editing_information( ). The V-phase extracted from the encoded stream represents the vertical position of the active video area in the full pixel area of the input video data while the H-phase represents the horizontal position of the active video area in the full pixel area of the input video data. Therefore, the controller  405  controls the base-band video generation circuit, in such a way that the decoded video data output from the buffer  415  will be mapped to the vertical and horizontal positions represented by V-phase and H-phase, on the full pixel area with the blanking image, or in such a way as to synthesize the decoded video data in the active area and blanking image in the full pixel area based on the vertical and horizontal positions represented by V-phase and H-phase. Consequently, the video data output from the base-band video generation circuit  416  has exactly the same blanking interval as the blanking interval in the input video data supplied to the MPEG encoder. 
     The controller  405  supplies Ancillary_data, Line_number, Field_ID, Time_code_ 1 , and Time_code_ 2  extracted from the encoded stream or controls the multiplexing process of the multiplexing circuit  417  for Ancillary_data, Time_code_ 1 , and Time_code_ 2 , based on Field_ID. Specifically, as described with reference to FIG. 7C, since Field_ID is associated with Ancillary_data assigned to each field, the multiplexing circuit  417  superimposes Ancillary_data associated with Field_ID during the blanking interval identified by Field_ID. For example, if Field_ID is “2,” it can be seen that this is the third field in the frame. Thus, in the encoded stream, Ancillary_data received as ancillary data associated with Field_ID of “2” is superimposed on the blanking interval of the third field with Field_ID of “2.” When superimposing Ancillary_data on the blanking interval, the multiplexing circuit  417  superimposes Ancillary_data at the line number specified by Line_number transmitted with Ancillary_data. 
     Therefore, the video data output from the multiplexing circuit  417  has exactly the same ancillary data at exactly the same line number, in the active video area of exactly the same location, in exactly the same blanking interval as the input video data supplied to the MPEG encoder. 
     Thus, according to this embodiment, any MPEG encoding or decoding performed during the transmission of video data from the sending system to the receiving system will not cause the information inherent to the input video data or the ancillary data added to the input video data to be lost. 
     Industrial Applicability 
     The present invention can be used at broadcasting stations and the like where video data is encoded and decoded frequently.