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nonsense (MPlayer container format draft 0.01)
git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@9295 b3059339-0415-0410-9bf9-f77b7e298cf2
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michael
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DOCS/tech/mpcf.txt
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415
DOCS/tech/mpcf.txt
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MPlayer container format draft 0.01
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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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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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gurantees that no mpeg startcode prefixes occur in the headers with the
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exception of codec specific headers (really?)
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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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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 v
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average_bitrate v
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language_code v
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time_base v
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lsb_timestamp_length v
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fixed_fps u(1)
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codec_specific_header_flag u(1)
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reserved u(6)
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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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codec_specific_header:
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packet_header
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codec_specific_startcode f(64)
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stream_id v
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codec_specific data
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checksum
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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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lsb_timestamp u(lsb_timestamp_length)
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stream_id u(log2_stream_count)
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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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align_byte
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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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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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checksum u(32)
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info_header: (optional)
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packet header
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info_startcode f(64)
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title sz
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author sz
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copyright sz
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description sz
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checksum u(32)
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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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value-=4
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sz (zero terminated string)
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for(i=0; next_byte != 0; i++){
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string[i] u(8)
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}
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zero_byte f(8)
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Note: the string MUST not be 0 bytes long (only a zero byte coded), instead
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{'?', 0} should be used instead
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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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forward_ptr
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backward_ptr
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pointer to the next / previous packet
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Note: a frame with 0 bytes means that its skiped
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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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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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if there is a stream with id n>0 then there MUST be a stream with id n-1
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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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fourcc
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identification for the codec
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example: 'h'<<24 + '2'<<16 + '6'<<8 + '4'
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language_code
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something like 'u'<<24 + 's'<<16 + 'e'<<8 + 'n' (US english), can be 0
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if unknown
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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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MUST be < 2^15
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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_header_flag
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1 indicates that this stream has a codec specific header
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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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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=0x04c11db7 (same as ogg)
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bit 23 is forced to 1 to avoid MPEG startcode emulation
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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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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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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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codec_specific_header (id=0)
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stream_header (id=1)
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codec_specific_header (id=1)
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...
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stream_header (id=n)
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codec_specific_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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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 - 4;
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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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val+=4;
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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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codec_specific_header (stream 0)
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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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codec_specific_header (stream 0)
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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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codec_specific_header (stream 0)
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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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