NUT Open Container Format DRAFT 20040409 ---------------------------------------- Intro: Features / goals: (supported by the format, not necessary by a specific implementation) Simple use the same encoding for nearly all fields simple decoding, so slow cpus (and embedded systems) can handle it Extendible no limit for the possible values for all fields (using universal vlc) allow adding of new headers in the future allow adding more fields at the end of headers Compact ~0.2% overhead, for normal bitrates index is <10kb per hour (1 keyframe every 3sec) a usual header for a file is about 100bytes (audio + video headers together) a packet header is about ~1-8 bytes Error resistant seeking / playback without an index headers & index can be repeated damaged files can be played back with minimal data lost and fast resyncing times Definitions: MUST the specific part must be done to conform to this standard SHOULD its recommanded to be done that way but its not strictly required Syntax: Type definitions: f(x) n fixed bits in big endian order u(x) unsigned number encoded in x bits in MSB first order v value=0 do{ more_data u(1) data u(7) value= 128*value + data }while(more_data) s temp v temp++ if(temp&1) value= -(temp>>1) else value= (temp>>1) b (binary data or string) for(i=0; i= tmp_mul){ tmp_size=0; tmp_stream++; } } } reserved_bytes checksum u(32) stream_header: stream_startcode f(64) packet_header stream_id v stream_class v fourcc vb average_bitrate v language_code vb time_base_nom v time_base_denom v msb_timestamp_shift v initial_timestamp_predictor v(3) initial_data_size_predictor v(2) fixed_fps u(1) index_flag u(1) reserved u(6) for(;;){ codec_specific_data_type v if(codec_specific_data_type==0) break; codec_specific_data vb } video_stream_header: stream_header width v height v sample_width v sample_height v colorspace_type v reserved_bytes checksum u(32) audio_stream_header: stream_header samplerate_mul v channel_count v reserved_bytes checksum u(32) frame if(frame_type == 2){ frame_type2_startcode f(64) } frame_code f(8) if(flags[frame_code]&1){ packet header } if(stream_id_plus1[frame_code]==0){ stream_id v } if(flags[frame_code]&16){ if(flags[frame_code]&4){ timestamp v }else{ lsb_timestamp v } } if(flags[frame_code]&2){ data_size_msb v } data Index: index_startcode f(64) packet header stream_id v index_length v for(i=0; i 0 stream_id MUST be < stream_count stream_class 0 video 32 audio 64 subtiles Note the remaining values are reserved and MUST NOT be used a demuxer MUST ignore streams with reserved classes fourcc identification for the codec example: "H264" MUST contain 2 or 4 bytes, note, this might be increased in the future if needed language_code ISO 639 and ISO 3166 for language/country code something like "usen" (US english), can be 0 if unknown see http://www.loc.gov/standards/iso639-2/englangn.html and http://www.din.de/gremien/nas/nabd/iso3166ma/codlstp1/en_listp1.html time_base_nom / time_base_denom = time_base the number of timer ticks per second, this MUST be equal to the fps if the fixed_fps is 1 time_base_denom MUST not be 0 time_base_nom and time_base_denom MUST be relative prime time_base_nom MUST be < 2^16 examples: fps time_base_nom time_base_denom 30 30 1 29.97 30000 1001 23.976 24000 1001 sample_rate sample_rate_mul time_base_nom time_base_denom 44100 1 44100 1 44100 64 11025 16 48000 1024 375 8 Note: the advantage to using a large sample_rate_mul is that the timestamps need fewer bits msb_timestamp_shift amount of bits msb_timestamp is shifted left before adding lsb_timestamp MUST be <16 fixed_fps 1 indicates that the fps is fixed index_flag 1 indicates that this file has an index Note, all files SHOULD have an index at the end except, (realtime) streams Note, all streams SHOULD have an index codec_specific_data_type 0 none/end 1 native 2 bitmapinfoheader 3 waveformatex 4 imagedesc 5 sounddesc "native", means a simple api & container independanet storage form, for example some mpeg4-es headers codec_specific_data private global data for a codec (could be huffman tables or ...) frame_code the meaning of this byte is stored in the main header the value 78 ('N') is forbidden to ensure that the byte is always different from the first byte of any startcode flags[frame_code] the bits of the flags from MSB to LSB are KKTTTDP P is 1 for type 1 and 2 packets, 0 for type 0 packets TTT is the timestamp_code, 000,001,010 use the last timestamp + the first, second and third last unique timestamp difference, so if the timestamp differences, are +3,+1,+2,+2,+1 then last diff is +1, second is +2 and third is +3 100,101 mean that the lsb or full timestamp is coded if TTT is 100, then the timestamp is calculated by mask = (1< no keyframe, 01-> keyframe, flags=1 can be used to mark illegal frame_code bytes frame_code=78 must have flags=1 frame_type 0       is indicated by (flags[frame_code]&1)==0 1       is indicated by (flags[frame_code]&1)==1 && !startcode 2       is indicated by (flags[frame_code]&1)==1 && startcode there SHOULD not be more then 0.5 seconds or 16kbyte of type 0 frames wihout a intervening frame of different frame_type * type 2 frames MUST be decodeable independantly of any other frames this means they MUST be keyframes and they MUST use a full timestamp * type 1 frames MUST not depend(1) upon any other frames, this means, they MUST use a full timestamp * type 0 frames MUST not depend(1) upon frames prior to the last type 1/2 frames depend(1) means dependancy on the container level (NUT) not dependancy on the codec level stream_id_plus1[frame_code] must be <250 if its 0 then the stream_id is coded in the frame data_size_mul[frame_code] must be <250 data_size_lsb[frame_code] must be <250 data_size if(data_size_lsb == data_size_mul) data_size= last; else if(data_size_lsb == data_size_mul+1) data_size= next_last; else if(data_size_lsb < data_size_mul) data_size= data_size_lsb + data_size_msb*data_size_mul; else reserved next_last is the second last unique data_size, for example: previous data_size: 123,500,312,500,500 last=500, next_last=312 last and next_last are reset to the initial_data_size_predictor values stored in the stream header if an frame with type > 0 is encountered lsb_timestamp least significant bits of the timestamp in time_base precission Example: IBBP display order keyframe timestamp=0 -> timestamp=0 frame lsb_timestamp=3 -> timestamp=3 frame lsb_timestamp=1 -> timestamp=1 frame lsb_timestamp=2 -> timestamp=2 ... keyframe msb_timestamp=257 -> timestamp=257 frame lsb_timestamp=255->timestamp=255 frame lsb_timestamp=0 -> timestamp=256 frame lsb_timestamp=4 -> timestamp=260 frame lsb_timestamp=2 -> timestamp=258 frame lsb_timestamp=3 -> timestamp=259 all timestamps of keyframes of a single stream MUST be monotone width/height MUST be set to the coded width/height sample_width/sample_height (aspect ratio) sample_width is the horizontal distance between samples sample_width and sample_height MUST be relative prime if not zero MUST be 0 if unknown colorspace_type 0 unknown 1 ITU Rec 624 / ITU Rec 601 Y range: 16..235 Cb/Cr range: 16..240 2 ITU Rec 709 Y range: 16..235 Cb/Cr range: 16..240 17 ITU Rec 624 / ITU Rec 601 Y range: 0..255 Cb/Cr range: 0..255 18 ITU Rec 709 Y range: 0..255 Cb/Cr range: 0..255 samplerate_mul the number of samples per second in one time_base unit samplerate = time_base*samplerate_mul zero_bit MUST be 0, its there to distinguish non keyframes from other packets, Note: all packets have a 64-bit startcode except non-keyframes to reduce their size, and all startcodes start with a 1 bit checksum adler32 checksum index_timestamp value in time_base precission, relative to the last index_timestamp index_position position in bytes of the first byte of the keyframe header, relative to the last index_position id the id of the type/name pair, so its more compact 0 means end type for example: "UTF8" -> String or "JPEG" -> jpeg image Note: nonstandard fields should be prefixed by "X-" Note: MUST be less than 6 byte long (might be increased to 64 later) name the name of the info entry, valid names are "TotalTime" total length of the stream in msecs "StreamId" the stream(s) to which the info packet applies "StartTimestamp" "EndTimestamp" the time range in msecs to which the info applies "SegmentId" a unique id for the streams + time specified "Author" "Description" "Copyright" "Encoder" the name & version of the software used for encoding "Title" "Cover" an image of the (cd,dvd,vhs,..) cover (preferable PNG or JPEG) "Source" "DVD", "VCD", "CD", "MD", "FM radio", "VHS", "TV", "LD" Optional: appended PAL,NTSC,SECAM, ... in parentheses "CaptureDevice" "BT878", "BT848", "webcam", ... (more exact names are fine too) "CreationTime" "2003-01-20 20:13:15Z", ... (ISO 8601 format, see http://www.cl.cam.ac.uk/~mgk25/iso-time.html) Note: dont forget the timezone "ReplayGain" "Keywords" Note: if someone needs some others, please tell us about them, so we can add them to the official standard (if they are sane) Note: nonstandard fields should be prefixed by "X-" Note: MUST be less than 64 bytes long value value of this name/type pair stuffing 0x80 can be placed infront of any type v entry for stuffing purposes info_table[][2]={ {NULL , NULL }, // end {NULL , NULL }, {NULL , "UTF8"}, {NULL , "v"}, {NULL , "s"}, {"StreamId" , "v"}, {"SegmentId" , "v"}, {"StartTimestamp" , "v"}, {"EndTimestamp" , "v"}, {"Author" , "UTF8"}, {"Titel" , "UTF8"}, {"Description" , "UTF8"}, {"Copyright" , "UTF8"}, {"Encoder" , "UTF8"}, {"Keyword" , "UTF8"}, {"Cover" , "JPEG"}, {"Cover" , "PNG"}, }; Structure: the headers MUST be in exactly the following order (to simplify demuxer design) main header stream_header (id=0) stream_header (id=1) ... stream_header (id=n) headers may be repated, but if they are then they MUST all be repeated together and repeated headers MUST be identical headers MUST be repeated every 10sec at least ? FIXME headers MUST be repeated BEFORE keyframes headers MUST be repeated at least twice (so they exist 3 times in a file) Index the index can be repeated but there SHOULD be at least one for each stream at the end Note: in case of realtime streaming there is no end, so no index there either Info packets the info_packet can be repeated, it can also contain different names & values each time but only if allso the time is different Info packets can be used to describe the file or some part of it (chapters) info packets, SHOULD be placed at the begin of the file at least for realtime streaming info packets will normally be transmitted when they apply for example, the current song title & artist of the currently shown music video Unknown packets MUST be ignored by the demuxer Sample code (GPL, & untested) typedef BufferContext{ uint8_t *buf; uint8_t *buf_ptr; }BufferContext; static inline uint64_t get_bytes(BufferContext *bc, int count){ uint64_t val=0; assert(count>0 && count<9) for(i=0; ibuf_ptr++); } return val; } static inline void put_bytes(BufferContext *bc, int count, uint64_t val){ uint64_t val=0; assert(count>0 && count<9) for(i=count-1; i>=0; i--){ *(bc->buf_ptr++)= val >> (8*i); } return val; } static inline uint64_t get_v(BufferContext *bc){ uint64_t val= 0; for(; space_left(bc) > 0; ){ int tmp= *(bc->buf_ptr++); if(tmp&0x80) val= (val<<7) + tmp - 0x80; else return (val<<7) + tmp; } return -1; } static inline int put_v(BufferContext *bc, uint64_t val){ int i; if(space_left(bc) < 9) return -1; val &= 0x7FFFFFFFFFFFFFFFULL; // FIXME can only encode upto 63 bits currently for(i=7; ; i+=7){ if(val>>i == 0) break; } for(i-=7; i>0; i-=7){ *(bc->buf_ptr++)= 0x80 | (val>>i); } *(bc->buf_ptr++)= val&0x7F; return 0; } Authors Folks from MPlayer Developers Mailinglist (http://www.mplayehrq.hu/). Authors in ABC-order: (FIXME! Tell us if we left you out) Beregszaszi, Alex (alex@fsn.hu) Bunkus, Moritz (moritz@bunkus.org) Diedrich, Tobias (td@sim.uni-hannover.de) Franz, Fabian (FabianFranz@gmx.de) Gereoffy, Arpad (arpi@thot.banki.hu) Hess, Andreas (jaska@gmx.net) Niedermayer, Michael (michaelni@gmx.at)