mirror of https://github.com/mpv-player/mpv
514 lines
14 KiB
Plaintext
514 lines
14 KiB
Plaintext
nut format draft 0.02
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Intro:
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Features / goals:
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(supported by the format, not necessary by a specific implementation)
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Simple
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use the same encoding for nearly all fields
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simple decoding, so slow cpus can handle it
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Extendible
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no limit for the possible values for all fields (using universal vlc)
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allow adding of new headers in the future
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allow adding more fields at the end of headers
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Compact
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~0.2% overhead, for normal bitrates
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index is <10kb per hour (1 keyframe every 3sec)
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Error resistant
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seeking / playback without an index
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headers & index can be repeated
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audio packet reshuffle
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checksums to allow quick redownloading of damaged parts
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Definitions:
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MUST the specific part must be done to conform to this standard
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SHOULD its recommanded to be done that way but its not strictly required
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Syntax:
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Type definitions:
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v
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value=0
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do{
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more_data u(1)
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data u(7)
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value= 128*value + data
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}while(more_data)
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b (binary data or string)
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length v
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for(i=0; i<length; i++){
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data[i] u(8)
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}
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Note: strings MUST be encoded in utf8
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f(x) n fixed bits
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u(x) unsigned number encoded in x bits in MSB first order
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Bitstream syntax:
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packet header
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forward ptr v
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backward ptr v
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align_byte
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while(not byte aligned)
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one f(1)
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reserved_bytes
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for(i=0; i<forward_ptr - length_of_non_reserved; i++)
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reserved u(8)
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main header:
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packet header
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main_startcode f(64)
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version v
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stream_count v
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file_size v
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length_in_msec v
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reserved_bytes
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checksum u(32)
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stream_header:
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packet_header
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stream_startcode f(64)
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stream_id v
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stream_class v
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fourcc b
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average_bitrate v
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language_code b
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time_base_nom v
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time_base_denom v
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lsb_timestamp_length v
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fixed_fps u(1)
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index_flag u(1)
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reserved u(6)
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codec_specific_data b
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video_stream_header:
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stream_header
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width v
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height v
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sample_width v
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sample_height v
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colorspace_type v
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depth v
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reserved_bytes
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checksum u(32)
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audio_stream_header:
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stream_header
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samplerate v
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channel_count v
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sub_packet_size v
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shuffle_type v
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reserved_bytes
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checksum u(32)
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frame
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packet header
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if(keyframe){
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keyframe_startcode f(64)
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}
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zero_bit f(1)
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priority u(2)
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checksum_flag u(1)
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msb_timestamp_flag u(1)
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reserved u(3)
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lsb_timestamp v
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stream_id v
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if(msb_timestamp_flag)
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msb_timestamp v
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bitstream
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if(checksum_flag)
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frame_checksum u(32)
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Index:
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packet header
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index_startcode f(64)
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stream_id v
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index_length v
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for(i=0; i<index_length; i++){
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index_timestamp v
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index_position v
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}
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reserved_bytes
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checksum u(32)
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info_packet: (optional)
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packet header
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info_startcode f(64)
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start_time v
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end_time v
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start_stream_id v
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end_stream_id v
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for(;;){
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type b
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if(type=="") break;
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name b
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value b
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}
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reserved_bytes
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checksum u(32)
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stuffing_packet: (optional)
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packet_header
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stuffing_startcode f(64)
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for(i=0; i<forward_ptr - length_of_non_reserved; i++)
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stuffing f(8)
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forward_ptr
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backward_ptr
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pointer to the next / previous packet
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pointers are relative and backward pointer is implicitelly negative
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Note: a frame with 0 bytes means that its skiped
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Note: the forward pointer is equal to the size of this packet including
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the header
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the backward pointer is equal to the size of the previous packet
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Example:
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0
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size1 (size of frame1 including header)
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frame1
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size1
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size2
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frame2
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size2
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size3
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frame3
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*_startcode
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the first bit is allways set
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version
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0 for now
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file_size
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size in bytes, can be 0 if not meaningfull (realtime streams, ...)
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length_in_msec
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length of the file in milli seconds (can be 0 if realtime or such)
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index_flag
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1 indicates that this file has an index
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Note, all files MUST have an index at the end except, (realtime) streams
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stream_id
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Note: streams with a lower relative class MUST have a lower relative id
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so a stream with class 0 MUST allways have a id which is lower then any
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stream with class > 0
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streams should use low ids
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stream_class
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0 video
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32 audio
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64 subtiles
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Note the remaining values are reserved and MUST NOT be used
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a decoder MUST ignore streams with reserved classes
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fourcc
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identification for the codec
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example: "H264"
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MUST contain 4 bytes, note, this might be increasd in the future if
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needed
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language_code
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ISO 639 and ISO 3166 for language/country code
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something like "usen" (US english), can be 0
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if unknown
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see http://www.loc.gov/standards/iso639-2/englangn.html
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and http://www.din.de/gremien/nas/nabd/iso3166ma/codlstp1/en_listp1.html
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time_base_nom / time_base_denom = time_base
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the number of timer ticks per second, this MUST be equal to the fps
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if the fixed_fps is 1
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time_base_denom MUST not be 0
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time_base_nom and time_base_denom MUST be relative prime
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time_base_nom MUST be < 2^15
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examples:
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fps time_base_nom time_base_denom
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30 30 1
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29.97 30000 1001
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23.976 24000 1001
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lsb_timestamp_length
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length in bits of the lsb_timestamp
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MUST be <16
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fixed_fps
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1 indicates that the fps is fixed
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codec_specific_data
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private global data for a codec (could be huffman tables or ...)
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msb_timestamp_flag
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indicates that the msb_timestamp is coded
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MUST be 1 for keyframes
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msb_timestamp
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most significant bits of the timestamp, SHOULD be 0 for the first frame
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lsb_timestamp
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most significant bits of the timestamp in time_base precission, with
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lsb_timestamp_length bits
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Example: IBBP display order
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keyframe msb_timestamp=0 lsb_timestamp=0 -> timestamp=0
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frame lsb_timestamp=3 -> timestamp=3
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frame lsb_timestamp=1 -> timestamp=1
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frame lsb_timestamp=2 -> timestamp=2
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...
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keyframe msb_timestamp=1 lsb_timestamp=1 -> timestamp=257
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frame msb_timestamp=0 lsb_timestamp=255->timestamp=255
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frame msb_timestamp=1 lsb_timestamp=0 -> timestamp=256
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frame lsb_timestamp=4 -> timestamp=260
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frame lsb_timestamp=2 -> timestamp=258
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frame lsb_timestamp=3 -> timestamp=259
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width/height
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MUST be set to the coded width/height
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sample_width/sample_height (aspect ratio)
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sample_width is the horizontal distance between samples
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sample_width and sample_height MUST be relative prime if not zero
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MUST be 0 if unknown
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depth
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for compatibility with some win32 codecs
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zero_bit
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MUST be 0, its there to distinguish non keyframes from other packets,
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Note: all packets have a 64-bit startcode except non-keyframes to reduce
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their size, and all startcodes start with a 1 bit
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priority
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if 0 then the frame isnt used as reference (b frame) and can be droped
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MUST be > 0 for keyframes
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sub_packet_size
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size of an audio packet
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Note a subpacket MUST be in exactly one packet, it cannot be split
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shuffle_type
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audio is often encoded in small fixed size packets, and to increase the
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error robustness these can be shuffled
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0 -> no shuffle
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1-16 -> interleave packets by 2^n
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checksum
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crc32 checksum using the generator polynomial 0x104c11db7 (same as ogg)
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checksum_flag
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indicates that the frame_checksum is coded
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must be 1 for the last non keyframe before a keyframe
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frame_checksum
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identical to checksum, but instead of covering just the current
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packet, it covers all frames of the same stream id since the last
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frame_checksum
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this field is only coded if checksum_flag=1
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index_timestamp
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value in time_base precission, relative to the last index_timestamp
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index_position
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position in bytes of the first byte of the keyframe header, relative
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to the last index_position
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start_time, stop_time
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the time range in msecs to which the info applies
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Note: can be used to mark chapters
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start_stream_id / end_stream_id
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the stream(s) to which the info packet applies
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type
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the fourcc of the type
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for example: "UTF8" -> String or "JPEG" -> jpeg image
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0 length means end
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name
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the name of the info entry, valid names are
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"Author"
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"Description"
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"Copyright"
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"Encoder" the name& version of the software used for encoding
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"Title"
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"CDCover" an image of the cd cover (preferable PNG or JPEG)
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"Source" "DVD", "VCD", "CD", "MD", "FM radio", "VHS", "TV",
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"LD"
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"CaptureDevice" "BT878", "BT848", "webcam", ... (more exact names are fine too)
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"CreationTime" "2003-01-20 20:13:15Z", ...
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(ISO 8601 format, see http://www.cl.cam.ac.uk/~mgk25/iso-time.html)
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Note: dont forget the timezone
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Note: if someone needs some others, please tell us about them, so we can
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add them to the official standard (if they are sane)
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value
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stuffing
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0xFF
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Structure:
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the headers MUST be in exactly the following order (to simplify demuxer design)
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main header
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stream_header (id=0)
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stream_header (id=1)
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...
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stream_header (id=n)
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headers may be repated, but if they are then they MUST all be repeated together
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and repeated headers MUST be identical
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headers MUST be repeated every 10sec at least ? FIXME
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headers MUST be repeated at least twice (so they exist 3 times in a file)
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Index
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the index can be repeated but there MUST be at least one at the end
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Note: in case of realtime streaming there is no end, so no index there either
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Info packets
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the info_packet can be repeated, it can also contain different names & values
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each time but only if allso the time is different
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Info packets can be used to describe the file or some part of it (chapters)
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info packets, SHOULD be placed at the begin of the file at least
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for realtime streaming info packets will normally be transmitted when they apply
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for example, the current song title & artist of the currently shown music video
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Stuffing packets
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can be used as a filler, for example to leave some empty space at the begin for
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a copy of the index
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Unknown packets
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MUST be ignored by the decoder
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Sample code (GPL, & untested)
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typedef BufferContext{
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uint8_t *buf;
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uint8_t *buf_ptr;
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}BufferContext;
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static inline uint64_t get_bytes(BufferContext *bc, int count){
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uint64_t val=0;
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assert(count>0 && count<9)
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for(i=0; i<count; i++){
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val <<=8;
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val += *(bc->buf_ptr++);
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}
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return val;
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}
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static inline void put_bytes(BufferContext *bc, int count, uint64_t val){
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uint64_t val=0;
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assert(count>0 && count<9)
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for(i=count-1; i>=0; i--){
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*(bc->buf_ptr++)= val >> (8*i);
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}
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return val;
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}
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static inline uint64_t get_v(BufferContext *bc){
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uint64_t val= 0;
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for(;;){
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int tmp= *(bc->buf_ptr++);
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if(tmp&0x80)
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val= (val<<7) + tmp - 0x80;
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else
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return (val<<7) + tmp;
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}
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}
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static inline void put_v(BufferContext *bc, uint64_t val){
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int i;
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assert(val);
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for(i=56;; i-=8){
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if(val>>i) break;
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}
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for(;i>0; i-=8){
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*(bc->buf_ptr++)= 0x80 | (val>>i);
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}
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*(bc->buf_ptr++)= val&0x7F;
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}
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Example stream
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main header
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video_stream_header (stream 0, video jpjp, timebase 30, lsb_timestamp_length=8)
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video_stream_header (stream 1 subtitle usen, timebase 30, lsb_timestamp_length=8)
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video_stream_header (stream 2 subtitle atde, timebase 30, lsb_timestamp_length=8)
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audio_stream_header (stream 3, audio jpjp, timebase 1 , lsb_timestamp_length=8)
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audio_stream_header (stream 4, audio usen, timebase 1 , lsb_timestamp_length=8)
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index (stream 0)
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keyframe (stream 0, msb_timestamp=0, lsb_timestamp=0)
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keyframe (stream 1, msb_timestamp=0, lsb_timestamp=0)
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keyframe (stream 2, msb_timestamp=0, lsb_timestamp=0)
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keyframe (stream 3, msb_timestamp=0, lsb_timestamp=0)
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keyframe (stream 4, msb_timestamp=0, lsb_timestamp=0)
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frame (stream 0, lsb_timestamp=1)
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frame (stream 0, lsb_timestamp=2)
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...
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frame (stream 0, lsb_timestamp=30)
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keyframe (stream 3, msb_timestamp=0, lsb_timestamp=1)
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keyframe (stream 4, msb_timestamp=0, lsb_timestamp=1)
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frame (stream 0, lsb_timestamp=31)
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frame (stream 0, lsb_timestamp=32)
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...
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frame (stream 0, lsb_timestamp=60)
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frame (stream 1, lsb_timestamp=60)
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frame (stream 2, lsb_timestamp=60)
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keyframe (stream 3, msb_timestamp=0, lsb_timestamp=2)
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keyframe (stream 4, msb_timestamp=0, lsb_timestamp=2)
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frame (stream 0, lsb_timestamp=61)
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frame (stream 0, lsb_timestamp=62)
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...
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main header
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video_stream_header (stream 0, video jpjp, timebase 30, lsb_timestamp_length=8)
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video_stream_header (stream 1 subtitle usen, timebase 30, lsb_timestamp_length=8)
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video_stream_header (stream 2 subtitle atde, timebase 30, lsb_timestamp_length=8)
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audio_stream_header (stream 3, audio jpjp, timebase 1 , lsb_timestamp_length=8)
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audio_stream_header (stream 4, audio usen, timebase 1 , lsb_timestamp_length=8)
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frame (stream 0, lsb_timestamp=255)
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frame (stream 0, msb_timestamp=1 lsb_timestamp=0)
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frame (stream 0, lsb_timestamp=1)
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frame (stream 0, lsb_timestamp=2)
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frame (stream 1, msb_timestamp=1 lsb_timestamp=2)
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frame (stream 2, msb_timestamp=1 lsb_timestamp=2)
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frame (stream 0, lsb_timestamp=3)
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frame (stream 0, lsb_timestamp=4)
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...
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keyframe (stream 3, msb_timestamp=0, lsb_timestamp=9)
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keyframe (stream 4, msb_timestamp=0, lsb_timestamp=9)
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main header
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video_stream_header (stream 0, video jpjp, timebase 30, lsb_timestamp_length=8)
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video_stream_header (stream 1 subtitle usen, timebase 30, lsb_timestamp_length=8)
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video_stream_header (stream 2 subtitle atde, timebase 30, lsb_timestamp_length=8)
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audio_stream_header (stream 3, audio jpjp, timebase 1 , lsb_timestamp_length=8)
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audio_stream_header (stream 4, audio usen, timebase 1 , lsb_timestamp_length=8)
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index (stream 0)
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