mpv/DOCS/tech/mpcf.txt

		NUT Open Container Format DRAFT 20030906
		----------------------------------------


                
			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 ~8 bytes
Error resistant
	seeking / playback without an index
	headers & index can be repeated
	audio packet reshuffle
	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
	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
	shuffle_type				v
	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(keyframe){
		keyframe_startcode		f(64)
	}
	zero_bit				f(1)
	priority				u(2)
	checksum_flag				u(1)
	msb_timestamp_flag			u(1)
	subpacket_type				u(2)
	reserved				u(1)
	packet header
	stream_id				v
	if(msb_timestamp_flag)
		msb_timestamp			v
	lsb_timestamp				s
	if(sub_packet_type==01)
		sub_packet[0]
	else{
		subpacket_count			v
		if(sub_packet_type&01)
		    for(i=0; ; i++)
			keyframe_run[i]		v
		for(i=0; ; i++){
		    timestamp_diff[i]		v
		    if(timestamp_diff[i] & 1)
			timestamp_diff_run[i]	v
		}
		if(sub_packet_type&10){
		    for(i=0; i<subpacket_count-1; i++)
			subpacket_size_diff[i]	s
		}
		for(i=0; i<subpacket_count; i++)
		    subpacket[i]
		}
	}
	if(checksum_flag)
		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

file_size
	size in bytes. 0 invalidates the field

length_in_msec
	length of the file in milli seconds (0 invalidates the field)
 
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 ...)
        
msb_timestamp_flag
	indicates that the msb_timestamp is coded
	MUST be 1 for keyframes
        
subpacket_type
		subpacket_count	subpacket_size	keyframe_flag
	00	>1		constant	constant
	01	1		NA		NA
	10	>1		variable	constant
	11	>1		variable	variable
	the only legal subpacket_type for video streams is 01, so video streams
	MUST NOT contain multiple subpackets per packet
	Note, if there are multiple subpackets then the timestamp of the packet
	is the timestamp of the first subpacket
	Note, if multiple subpackets are stored in one frame then the resulting
	framesize SHOULD be < 16kbyte and not more then 0.5 sec of data SHOULD
	be put in a single packet

subpacket_count
	the number of subpackets, if not pressent then 1

keyframe_run[i]
	the number of subpackets with an identical keyframe_flag
	Note, the value of first flag is stored in the packet header
	is equal to subpacket count if not coded

timestamp_diff[i]
	the difference from the last subpacket timestamp to the current one in
	time_base precission
	the lowwest bit is used to indicate if timestamp_diff_run[i] is coded

timestamp_diff_run[i]
	the number of subpackets which have the same timestamp_diff
	if not coded than 1
	0 is forbidden
        
subpacket_size_diff
	the difference between the predicted size of this subpacket and the
	actual size
	the predicted size is 64 for the first subpacket in a packet
	otherwise it is MAX(64, last_subpacket_size)
	the size of the last subpacket is not coded and is simply the space left
	Note a subpacket MUST be in exactly one packet, it cannot be split
       
msb_timestamp
	most significant bits of the timestamp, SHOULD be 0 for the first frame
 
lsb_timestamp
	difference from the msb_timestamp in time_base precission
        Example: IBBP display order
		keyframe msb_timestamp=0 lsb_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=1 lsb_timestamp=1 -> timestamp=257
		frame                    lsb_timestamp=-1-> 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
        
priority
	if 0 then the frame isnt used as reference (b frame) and can be droped
	MUST be > 0 for keyframes

shuffle_type
	audio is often encoded in small subpackets, and to increase the
	error robustness these can be shuffled
	0 -> no shuffle
	1-16 -> interleave packets by 2^n 

checksum
	crc32 checksum using the generator polynomial 0x104c11db7 (same as ogg)

checksum_flag
	indicates that the frame_checksum is coded
	must be 1 for the last non keyframe before a keyframe
        
frame_checksum
	identical to checksum, but instead of covering just the current 
	packet, it covers all frames of the same stream id since the last
	frame_checksum
	this field is only coded if checksum_flag=1
        
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
	"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;
}

static inline int put_s(BufferContext *bc, uint64_t val){
	if(val<=0) return put_v(bc, -2*val  );
	else       return put_v(bc,  2*val-1);
}

static inline int64_t get_s(BufferContext *bc){
	int64_t v= get_v(bc) + 1;
	if(v&1) return -(v>>1);
	else    return  (v>>1);
}

                
			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)