mirror of
https://github.com/mpv-player/mpv
synced 2025-04-01 23:00:41 +00:00
some comments and whitespace changes by (Luca Barbato <lu_zero gentoo org>)
git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@14855 b3059339-0415-0410-9bf9-f77b7e298cf2
This commit is contained in:
michael
parent
28eb814b53
commit
f4462dccd7
@ -37,12 +37,37 @@ SHOULD its recommanded to be done that way but its not strictly required
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Syntax:
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Since nut heavly uses variable lenght fields the simplest way to describe it
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is using a pseudocode approach.
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Conventions:
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The data tipes have a name, used in the bitstream syntax description, a short
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text description and a pseudocode (functional) definition, optional notes may
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follow:
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name (text description)
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functional definition
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[Optional notes]
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The bitream syntax element have a tagname and a functional definition, they are
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presented in a bottom up approach, again optional notes may follow and are reproduced in the tag description:
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name: (optional note)
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functional definition
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[Optional notes]
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The in-depth tag description follows the bitstream syntax.
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The functional definition has a C like syntax.
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Type definitions:
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f(x) n fixed bits in big-endian order
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u(x) unsigned number encoded in x bits in MSB first order
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v
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f(n) (n fixed bits in big-endian order)
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u(n) (unsigned number encoded in n bits in MSB first order)
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v (variable length value, unsigned)
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value=0
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do{
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more_data u(1)
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@ -50,38 +75,43 @@ v
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value= 128*value + data
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}while(more_data)
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s
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s (variable length value, signed)
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temp v
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temp++
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if(temp&1) value= -(temp>>1)
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else value= (temp>>1)
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b (binary data or string)
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b (binary data or string, to be use in vb, see below)
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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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[Note: strings MUST be encoded in utf8]
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vb
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vb (variable lenght binary data or string)
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length v
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value b
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Bitstream syntax:
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packet header
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Common elements:
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packet header:
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forward ptr v
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align_byte
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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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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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a demuxer MUST ignore any reserved bytes
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[a demuxer MUST ignore any reserved bytes
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a muxer MUST NOT write any reserved bytes, as this would make it
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inpossible to add new fields at the end of packets in the future in
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a compatible way
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impossible to add new fields at the end of packets in the future in
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a compatible way]
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Headers:
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main header:
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main_startcode f(64)
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@ -152,8 +182,9 @@ audio_stream_header:
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reserved_bytes
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checksum u(32)
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Basic Packets:
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frame
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frame:
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frame_code f(8)
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if(stream_id_plus1[frame_code]==0){
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stream_id v
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@ -168,7 +199,7 @@ frame
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reserved v
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data
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Index:
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index:
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index_startcode f(64)
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packet header
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stream_id v
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@ -200,11 +231,13 @@ info_packet: (optional)
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reserved_bytes
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checksum u(32)
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sync_point
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sync_point:
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frame_startcode f(64)
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global_timestamp v
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file
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Complete definition:
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file:
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file_id_string
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while(!eof && next_code != index_startcode){
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main_header
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@ -226,9 +259,14 @@ file
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}
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index
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Tag description:
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forward_ptr
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size of the packet (exactly the distance from the first byte of the
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startcode of the current packet to the first byte of the following packet
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startcode of the current packet to the first byte of the following
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packet
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file_id_string
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"nut/multimedia container\0"
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@ -238,13 +276,16 @@ file_id_string
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main_startcode
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0x7A561F5F04ADULL + (((uint64_t)('N'<<8) + 'M')<<48)
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stream_starcode
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0x11405BF2F9DBULL + (((uint64_t)('N'<<8) + 'S')<<48)
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frame_startcode
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0xE4ADEECA4569ULL + (((uint64_t)('N'<<8) + 'K')<<48)
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frame_startcodes SHOULD be placed immedeatly before a keyframe if the
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previous frame of the same stream was a non-keyframe, unless such
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non-keyframe - keyframe tansitions are very frequent
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non-keyframe - keyframe transitions are very frequent
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index_startcode
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0xDD672F23E64EULL + (((uint64_t)('N'<<8) + 'X')<<48)
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@ -252,25 +293,27 @@ info_startcode
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0xAB68B596BA78ULL + (((uint64_t)('N'<<8) + 'I')<<48)
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version
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2 for now
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NUT version, the current values is 2
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max_distance
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max distance of frame_startcodes, the distance may only be larger if
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there is only a single frame between the 2 frame_startcodes
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this can be used by the demuxer to detect damaged frame headers if the
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damage results in a too long chain
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SHOULD be set to <=32768 or at least <=65536 unless there is a very good
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reason to set it higher otherwise reasonable error recovery will be
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impossible
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there is only a single frame between the 2 frame_startcodes this can
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be used by the demuxer to detect damaged frame headers if the damage
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results in a too long chain
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SHOULD be set to <=32768 or at least <=65536 unless there is a very
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good reason to set it higher otherwise reasonable error recovery will
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be impossible
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max_index_distance
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max distance of keyframes which are represented in the index, the
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distance between consecutive entries A and B may only be larger if
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there are no keyframes within this stream between A and B
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SHOULD be set to <=32768 or at least <=65536 unless there is a very good
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reason to set it higher
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SHOULD be set to <=32768 or at least <=65536 unless there is a very
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good reason to set it higher
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stream_id[FIXME]
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Stream identifier
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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 always have a id which is lower then any
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stream with class > 0
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@ -281,7 +324,7 @@ stream_class
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1 audio
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2 subtiles
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3 metadata
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Note the remaining values are reserved and MUST NOT be used
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Note: the remaining values are reserved and MUST NOT be used
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a demuxer MUST ignore streams with reserved classes
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fourcc
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@ -305,8 +348,9 @@ time_base_nom / time_base_denom = time_base
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44100 1 44100 1
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44100 64 11025 16
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48000 1024 375 8
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Note: the advantage to using a large sample_rate_mul is that the
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timestamps need fewer bits
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Note: the advantage to using a large sample_rate_mul is that
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the timestamps need fewer bits
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global_time_base_nom / global_time_base_denom = global_time_base
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the number of timer ticks per second
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@ -316,14 +360,15 @@ global_time_base_nom / global_time_base_denom = global_time_base
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global_timestamp
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timestamp in global_time_base units
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when a global_timestamp is encountered the last_timestamp of all streams
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is set to the following:
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when a global_timestamp is encountered the last_timestamp of all
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streams is set to the following:
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ln= global_time_base_denom*time_base_nom
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sn= global_timestamp
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d1= global_time_base_nom
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d2= time_base_denom
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last_timestamp= (ln/d1*sn + ln%d1*sn/d1)/d2
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Note, this calculation MUST be done with unsigned 64 bit integers, and
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Note: this calculation MUST be done with unsigned 64 bit integers, and
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is equivalent to (ln*sn)/(d1*d2) but this would require a 96bit integer
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msb_timestamp_shift
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@ -331,10 +376,10 @@ msb_timestamp_shift
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MUST be <16
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decode_delay
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maximum time between input and output for a codec, used to generate dts
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from pts
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is 0 for streams without b frames, and 1 for streams with b frames, may
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be larger for future codecs
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maximum time between input and output for a codec, used to generate
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dts from pts
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is set to 0 for streams without b frames, and set to 1 for streams with
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b frames, may be larger for future codecs
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fixed_fps
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1 indicates that the fps is fixed
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@ -348,17 +393,17 @@ frame_code
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different from the first byte of any startcode
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flags[frame_code]
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the bits of the flags from MSB to LSB are KD
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first of the flags from MSB to LSB are called KD
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if D is 1 then data_size_msb is coded, otherwise data_size_msb is 0
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K is the keyframe_type
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0-> no keyframe,
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1-> keyframe,
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flags=4 can be used to mark illegal frame_code bytes
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frame_code=78 must have flags=4
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* frames MUST not depend(1) upon frames prior to the last
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Note: frames MUST not depend(1) upon frames prior to the last
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frame_startcode
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depend(1) means dependancy on the container level (NUT) not dependancy
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on the codec level
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Important: depend(1) means dependancy on the container level (NUT) not
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dependancy on the codec level
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stream_id_plus1[frame_code]
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must be <250
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@ -377,8 +422,8 @@ data_size
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data_size= data_size_lsb + data_size_msb*data_size_mul;
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coded_timestamp
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if coded_timestamp < (1<<msb_timestamp_shift) then its a
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lsb timestamp, otherwise its a full timestamp + (1<<msb_timestamp_shift)
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if coded_timestamp < (1<<msb_timestamp_shift) then its a lsb
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timestamp, otherwise its a full timestamp + (1<<msb_timestamp_shift)
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lsb timestamps are converted to full timesamps by:
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mask = (1<<msb_timestamp_shift)-1;
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delta= last_timestamp - mask/2
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@ -387,7 +432,7 @@ coded_timestamp
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available after the last frame_startcode with the current stream_id
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lsb_timestamp
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least significant bits of the timestamp in time_base precission
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least significant bits of the timestamp in time_base precision
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Example: IBBP display order
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keyframe timestamp=0 -> timestamp=0
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frame lsb_timestamp=3 -> timestamp=3
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@ -405,8 +450,8 @@ lsb_timestamp
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dts
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dts are calculated by using a decode_delay+1 sized buffer for each
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stream, into which the current pts is inserted and the element with
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the smallest value is removed, this is then the current dts
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this buffer is initalized with decode_delay -1 elements
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the smallest value is removed, this is then the current dts this
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buffer is initalized with decode_delay -1 elements
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all frames with dts == timestamp must be monotone, that means a frame
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which occures later in the stream must have a larger or equal dts
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then an earlier frame
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@ -487,8 +532,7 @@ value
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value of this name/type pair
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stuffing
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0x80 can be placed infront of any type v entry for stuffing
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purposes
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0x80 can be placed in front of any type v entry for stuffing purposes
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info_table[][2]={
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{NULL , NULL }, // end
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@ -520,9 +564,9 @@ 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 MAY only repeated at the closest possible positions after 2^x where x is
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an integer and the file end, so the headers may be repeated at 4102 if thats the
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closest possition after 2^12=4096 at which the headers can be placed
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headers MAY only repeated at the closest possible positions after 2^x where x
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is an integer and the file end, so the headers may be repeated at 4102 if that
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is the closest possition after 2^12=4096 at which the headers can be placed
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headers MUST be placed at least at the begin of the file and immedeatly before
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the index or at the file end if there is no index
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@ -544,9 +588,9 @@ the info_packet can be repeated, it can also contain different names & values
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each time but only if also 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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info packets, SHOULD be placed at the begin of the file at least for realtime
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streaming info packets will normally be transmitted when they apply for
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example, the current song title & artist of the currently shown music video
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Unknown packets
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MUST be ignored by the demuxer
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@ -554,8 +598,8 @@ MUST be ignored by the demuxer
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demuxer (non-normative)
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in the absence of valid header at beginning, players SHOULD search for backup
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headers starting at offset 2^x for each x players SHOULD end their search from a
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particular offset when any startcode is found (including syncpoint)
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headers starting at offset 2^x for each x players SHOULD end their search from
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a particular offset when any startcode is found (including syncpoint)
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Sample code (GPL, & untested)
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