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mpv/DOCS/tech/mpcf.txt

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NUT Open Container Format DRAFT 20040330
----------------------------------------
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
checksums to allow quick redownloading of damaged parts
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:
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)
length v
for(i=0; i<length; i++){
data[i] u(8)
}
Note: strings MUST be encoded in utf8
f(x) n fixed bits in big endian order
u(x) unsigned number encoded in x bits in MSB first order
Bitstream syntax:
packet header
forward ptr v
backward ptr v
align_byte
while(not byte aligned)
one f(1)
reserved_bytes
for(i=0; i<forward_ptr - length_of_non_reserved; i++)
reserved u(8)
a decoder MUST ignore any reserved bytes
a encoder MUST NOT write any reserved bytes, as this would make it
inpossible to add new fields at the end of packets in the future in
a compatible way
main header:
main_startcode f(64)
packet header
version v
stream_count v
checksum_threshold v
for(i=0; i<256; ){
tmp_flag v
tmp_stream v
tmp_mul v
tmp_size v
count v
for(j=0; j<count; j++, i++){
flags[i]= tmp_flag;
stream_id_plus1[i]= tmp_stream;
data_size_mul[i]= tmp_mul;
data_size_lsb[i]= tmp_size;
if(++tmp_size >= 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 b
average_bitrate v
language_code b
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_size v
codec_specific_data b
}
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
if(checksum_threshold < frame_type)
frame_checksum u(32)
Index:
index_startcode f(64)
packet header
stream_id v
index_length v
for(i=0; i<index_length; i++){
index_timestamp v
index_position v
}
reserved_bytes
checksum u(32)
info_packet: (optional)
info_startcode f(64)
packet header
for(;;){
id v
if(id==0) break
name= info_table[id][0]
type= info_table[id][1]
if(type==NULL)
type b
if(name==NULL)
name b
if(type=="v")
value v
else if(type=="s")
value s
else
value b
}
reserved_bytes
checksum u(32)
forward_ptr
backward_ptr
pointer to the next / previous packet
pointers are relative and backward pointer is implicitelly negative
Note: a frame with 0 bytes means that its skiped
Note: the forward pointer is equal to the size of this packet including
the header
the backward pointer is equal to the size of the previous packet
Example:
0
size1 (size of frame1 including header)
frame1
size1
size2
frame2
size2
size3
frame3
*_startcode
the first bit is allways set
version
0 for now
stream_id
Note: streams with a lower relative class MUST have a lower relative id
so a stream with class 0 MUST allways have a id which is lower then any
stream with class > 0
streams should use low ids
stream_class
0 video
32 audio
64 subtiles
Note the remaining values are reserved and MUST NOT be used
a decoder 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<<msb_timestamp_shift)-1;
delta= last_timestamp - mask/2
timestamp= ((timestamp_lsb-delta)&mask) + delta
TTT must be 100 or 101 if the packet_type is not 0
the last timestamp differences are reset to the default values
from the stream header if a packet of type not 0 in encountered
if D is 1 then data_size_msb is coded, otherwise its 0
KK is the keyframe_type
00-> no keyframe,
01-> keyframe,
10-> equal to last of the same stream,
11-> opposite from last of the same stream
KK must be 00 or 01 if the packet_type is not 0
flags=1 can be used to mark illegal frame_code bytes
frame_code=78 must have flags=1
frame_type
0<><30><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>is indicated by (flags[frame_code]&1)==0
1<><31><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>is indicated by (flags[frame_code]&1)==1 && !startcode
2<><32><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>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
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
last and next last are reset to the 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
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
crc32 checksum using the generator polynomial 0x104c11db7 (same as ogg)
frame_checksum
identical to checksum, but instead of covering just the current
packet, it covers all frames since the last frame_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
Stuffing packets
can be used as a filler, for example to leave some empty space at the begin for
a copy of the index
Unknown packets
MUST be ignored by the decoder
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; i<count; i++){
val <<=8;
val += *(bc->buf_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;
}
Example stream
main header
video_stream_header (stream 0, video jpjp, timebase 30, lsb_timestamp_length=8)
video_stream_header (stream 1 subtitle usen, timebase 30, lsb_timestamp_length=8)
video_stream_header (stream 2 subtitle atde, timebase 30, lsb_timestamp_length=8)
audio_stream_header (stream 3, audio jpjp, timebase 1 , lsb_timestamp_length=8)
audio_stream_header (stream 4, audio usen, timebase 1 , lsb_timestamp_length=8)
index (stream 0)
keyframe (stream 0, msb_timestamp=0, lsb_timestamp=0)
keyframe (stream 1, msb_timestamp=0, lsb_timestamp=0)
keyframe (stream 2, msb_timestamp=0, lsb_timestamp=0)
keyframe (stream 3, msb_timestamp=0, lsb_timestamp=0)
keyframe (stream 4, msb_timestamp=0, lsb_timestamp=0)
frame (stream 0, lsb_timestamp=1)
frame (stream 0, lsb_timestamp=2)
...
frame (stream 0, lsb_timestamp=30)
keyframe (stream 3, msb_timestamp=0, lsb_timestamp=1)
keyframe (stream 4, msb_timestamp=0, lsb_timestamp=1)
frame (stream 0, lsb_timestamp=31)
frame (stream 0, lsb_timestamp=32)
...
frame (stream 0, lsb_timestamp=60)
frame (stream 1, lsb_timestamp=60)
frame (stream 2, lsb_timestamp=60)
keyframe (stream 3, msb_timestamp=0, lsb_timestamp=2)
keyframe (stream 4, msb_timestamp=0, lsb_timestamp=2)
frame (stream 0, lsb_timestamp=61)
frame (stream 0, lsb_timestamp=62)
...
main header
video_stream_header (stream 0, video jpjp, timebase 30, lsb_timestamp_length=8)
video_stream_header (stream 1 subtitle usen, timebase 30, lsb_timestamp_length=8)
video_stream_header (stream 2 subtitle atde, timebase 30, lsb_timestamp_length=8)
audio_stream_header (stream 3, audio jpjp, timebase 1 , lsb_timestamp_length=8)
audio_stream_header (stream 4, audio usen, timebase 1 , lsb_timestamp_length=8)
frame (stream 0, lsb_timestamp=255)
frame (stream 0, msb_timestamp=1 lsb_timestamp=0)
frame (stream 0, lsb_timestamp=1)
frame (stream 0, lsb_timestamp=2)
frame (stream 1, msb_timestamp=1 lsb_timestamp=2)
frame (stream 2, msb_timestamp=1 lsb_timestamp=2)
frame (stream 0, lsb_timestamp=3)
frame (stream 0, lsb_timestamp=4)
...
keyframe (stream 3, msb_timestamp=0, lsb_timestamp=9)
keyframe (stream 4, msb_timestamp=0, lsb_timestamp=9)
main header
video_stream_header (stream 0, video jpjp, timebase 30, lsb_timestamp_length=8)
video_stream_header (stream 1 subtitle usen, timebase 30, lsb_timestamp_length=8)
video_stream_header (stream 2 subtitle atde, timebase 30, lsb_timestamp_length=8)
audio_stream_header (stream 3, audio jpjp, timebase 1 , lsb_timestamp_length=8)
audio_stream_header (stream 4, audio usen, timebase 1 , lsb_timestamp_length=8)
index (stream 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)
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