NUT Open Container Format DRAFT 20050111 ---------------------------------------- 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 it's recommended to be done that way, but it's not strictly required Syntax: Since nut heavily uses variable length fields, the simplest way to describe it is using a pseudocode approach. Conventions: The data types have a name, used in the bitstream syntax description, a short text description and a pseudocode (functional) definition, optional notes may follow: name (text description) functional definition [Optional notes] The bitstream syntax elements have a tagname and a functional definition, they are presented in a bottom up approach, again optional notes may follow and are reproduced in the tag description: name: (optional note) functional definition [Optional notes] The in-depth tag description follows the bitstream syntax. The functional definition has a C like syntax. Type definitions: f(n) (n fixed bits in big-endian order) u(n) (unsigned number encoded in n bits in MSB first order) v (variable length value, unsigned) value=0 do{ more_data u(1) data u(7) value= 128*value + data }while(more_data) s (variable length value, signed) temp v temp++ if(temp&1) value= -(temp>>1) else value= (temp>>1) b (binary data or string, to be use in vb, see below) for(i=0; i0) tmp_timestamp s if(tmp_fields>1) tmp_mul v if(tmp_fields>2) tmp_stream v if(tmp_fields>3) tmp_size v else tmp_size=0 if(tmp_fields>4) tmp_res v else tmp_res=0 if(tmp_fields>5) count v else count= tmp_mul - tmp_size for(j=6; j 0 stream_id MUST be < stream_count stream_class 0 video 1 audio 2 subtiles 3 metadata 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 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 relatively prime time_base_nom MUST be < 2^31 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 global_time_base_nom / global_time_base_denom = global_time_base the number of timer ticks per second global_time_base_denom MUST NOT be 0 global_time_base_nom and global_time_base_denom MUST be relatively prime global_time_base_nom MUST be < 2^31 global_timestamp timestamp in global_time_base units when a global_timestamp is encountered the last_timestamp of all streams is set to the following: ln= global_time_base_denom*time_base_nom sn= global_timestamp d1= global_time_base_nom d2= time_base_denom last_timestamp= (ln/d1*sn + ln%d1*sn/d1)/d2 Note: this calculation MUST be done with unsigned 64 bit integers, and is equivalent to (ln*sn)/(d1*d2) but this would require a 96bit integer msb_timestamp_shift amount of bits in lsb_timestamp MUST be <16 decode_delay maximum time between input and output for a codec, used to generate dts from pts is set to 0 for streams without b frames, and set to 1 for streams with b frames, may be larger for future codecs fixed_fps 1 indicates that the fps is fixed 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] first of the flags from MSB to LSB are called KD if D is 1 then data_size_msb is coded, otherwise data_size_msb is 0 K is the keyframe_type 0-> no keyframe, 1-> keyframe, flags=4 can be used to mark illegal frame_code bytes frame_code=78 must have flags=4 Note: frames MUST NOT depend(1) upon frames prior to the last frame_startcode Important: depend(1) means dependency on the container level (NUT) not dependency on the codec level stream_id_plus1[frame_code] must be <250 if it is 0, then the stream_id is coded in the frame data_size_mul[frame_code] must be <16384 data_size_lsb[frame_code] must be <16384 timestamp_delta[frame_code] must be <16384 and >-16384 data_size data_size= data_size_lsb + data_size_msb*data_size_mul; coded_timestamp if coded_timestamp < (1< 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 dts dts is calculated by using a decode_delay+1 sized buffer for each stream, into which the current pts is inserted and the element with the smallest value is removed, this is then the current dts this buffer is initalized with decode_delay -1 elements all frames with dts == timestamp must be monotone, that means a frame which occures later in the stream must have a larger or equal dts than an earlier frame FIXME rename timestamp* to pts* ? 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 relatively 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_nom / samplerate_denom = samplerate the number of samples per second checksum adler32 checksum index_timestamp value of the timestamp of a keyframe relative to the last keyframe stored in this index index_position position in bytes of the first byte of a keyframe, relative to the last keyframe stored in this index there MUST be no keyframe with the same stream_id as this index between 2 consecutive index entries if they are more than max_index_distance apart id the id of the type/name pair, so it's 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) info packet types the name of the info entry, valid names are "StreamId" the stream(s) to which the info packet applies "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: don't forget the timezone "Keywords" "TotalTime" total length of the stream in msecs "Language" ISO 639 and ISO 3166 for language/country code something like "eng" (US english), can be 0 if unknown and "multi" if several languages see http://www.loc.gov/standards/iso639-2/englangn.html and http://www.din.de/gremien/nas/nabd/iso3166ma/codlstp1/en_listp1.html the language code "Disposition" "original", "dub" (translated), "comment", "lyrics", "karaoke" 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 in front of any type v entry for stuffing purposes info_table[][2]={ {NULL , NULL }, // end {NULL , NULL }, {NULL , "UTF8"}, {NULL , "v"}, {NULL , "s"}, {"StreamId" , "v"}, {"Author" , "UTF8"}, {"Titel" , "UTF8"}, {"Language" , "UTF8"}, {"Description" , "UTF8"}, {"Copyright" , "UTF8"}, {"Encoder" , "UTF8"}, {"Keyword" , "UTF8"}, {"Cover" , "JPEG"}, {"Cover" , "PNG"}, {"Disposition" , "UTF8"}, }; 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 repeated, but if they are, then they MUST all be repeated together and repeated headers MUST be identical headers MAY only repeat at the closest possible positions after 2^x where x is an integer and the file end, so the headers may be repeated at 4102 if that is the closest position after 2^12=4096 at which the headers can be placed headers MUST be placed at least at the start of the file and immediately before the index or at the file end if there is no index headers MUST be repeated at least twice (so they exist 3 times in a file) a demuxer MUST NOT demux a stream which contains more than one stream, or which is wrapped in a structure to facilitate more than one stream or otherwise duplicate the role of a container. any such file is to be considered invalid info packets which describe the whole file or individual streams/tracks MUST be placed before any video/audio/... frames Index Note: with realtime streaming, there is no end, so no index there either Info packets the info_packet can be repeated, and can also contain different names & values each time, but only if 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 start 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 demuxer (non-normative) in the absence of valid header at beginning, players SHOULD search for backup headers starting at offset 2^x for each x players SHOULD end their search from a particular offset when any startcode is found (including syncpoint) 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; } static int64_t get_dts(int64_t pts, int64_t *pts_cache, int delay, int reset){ if(reset) memset(pts_cache, -1, delay*sizeof(int64_t)); while(delay--){ int64_t t= pts_cache[delay]; if(t < pts){ pts_cache[delay]= pts; pts= t; } } return pts; } 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 (ranma+mplayer@tdiedrich.de) Felker, Rich (dalias@aerifal.cx) Franz, Fabian (FabianFranz@gmx.de) Gereoffy, Arpad (arpi@thot.banki.hu) Hess, Andreas (jaska@gmx.net) Niedermayer, Michael (michaelni@gmx.at)