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yuv4mpeg(5)		      MJPEG Tools Manual		   yuv4mpeg(5)

NAME
       YUV4MPEG2 - video stream	format used by pipe-based MJPEGtools

DESCRIPTION
       Many  of	 the  MJPEGtools  communicate via pipes	and act	as filters (or
       sources or sinks).  The format of video data used in the	pipes  is  re-
       ferred  to as "YUV4MPEG", or, more precisely, "YUV4MPEG2".  (The	format
       was extended and	codified during	v1.5.x of the tools.)

       The basic structure is a	stream header followed by an unlimited	number
       of  frames.   Each  frame itself	consists of a header followed by video
       data.  The headers are vaguely human-readable ASCII, but	the video data
       is simple byte-size binary.

       The  MJPEGtools distribution has	a C library (libmjpegutils) which con-
       tains functions for manipulating	YUV4MPEG2 streams.  We recommend  that
       you  use	 this  library	rather than writing your own code if possible.
       See the header file "yuv4mpeg.h"	for a description of these functions.

       Design Goals:

       o      Easy to parse both via C or sh.

       o      Extensible; easy to add new parameters while  maintaining	 back-
	      wards compatibility.

       o      Simple upgrade from original "YUV4MPEG" format.

       Drawbacks:

       o      Frame  headers  do  not  have  constant size, so streams are not
	      seekable.

GRAMMAR
       The precise description of the the YUV4MPEG2 stream format is  as  fol-
       lows:

       STREAM consists of

       -  one STREAM-HEADER

       -  unlimited number of FRAMEs

       STREAM-HEADER consists of

       -  magic	string "YUV4MPEG2"

       -  unlimited  number  of	TAGGED-FIELDs, each preceeded by a ' ' (single
	  space) separator

       -  single '\n' line terminator

       FRAME consists of

       -  one FRAME-HEADER

       -  "length" octets of planar YCbCr 4:2:0	image data (If the  stream  is
	  interlaced,  then  the  two  fields  per frame are interleaved, with
	  proper spatial ordering.)

       FRAME-HEADER consists of

       -  magic	string "FRAME"

       -  unlimited number of TAGGED-FIELDs, each preceeded by a  ' '  (single
	  space) separator

       -  single '\n' line terminator

       TAGGED-FIELD consists of

       -  single ASCII character tag

       -  VALUE	(which does not	contain	whitespace)

       VALUE consists of

       -  RATIO, or

       -  integer (base	10 ASCII representation), or

       -  single ascii character, or

       -  string (multiple ASCII characters)

       RATIO consists of

       -  numerator (base 10 ASCII integer)

       -  ':' (a colon)

       -  denominator (base 10 ASCII integer)

       Header tags fall	into three categories:	optional, required and has-de-
       fault.  Optional	tags are completely optional and may be	omitted	from a
       header.	 Required  tags	must be	present	in a header.  Has-Default tags
       have a default value which is implied if	the tag	is not present.	 Inde-
       pendent	of  these  categories,	some tags allow	an "unknown" value and
       some do not.

       The supported tags for the STREAM-HEADER:

	      W[integer] - frame width in pixels, must be > 0 (required)

	      H[integer] - frame height	in pixels, must	be > 0 (required)

	      C[string]	- chroma subsampling, image data format	(has default)
		      420jpeg  - 4:2:0 with JPEG/MPEG-1	siting (default)
		      420mpeg2 - 4:2:0 with MPEG-2 siting
		      420paldv - 4:2:0 with PAL-DV siting
		      411      - 4:1:1,	cosited
		      422      - 4:2:2,	cosited
		      444      - 4:4:4 (no subsampling)
		      444alpha - 4:4:4 with an alpha channel
		      mono     - luma (Y') plane only

	      I[char] -	interlacing specification:  (has default)
		      ?	- unknown (default)
		      p	- progressive/none
		      t	- top-field-first
		      b	- bottom-field-first
		      m	- mixed-mode: refer to 'I' tag in frame	header

	      F[ratio] - frame-rate (has default of 0:0	== unknown)

	      A[ratio] - sample	aspect ratio (has default of 0:0 == unknown)

	      X[string]	- 'metadata' (optional;	unparsed, but passed around)

       The currently supported tags for	the FRAME-HEADER:

	      I[string]	- framing and sampling (required if-and-only-if	Im  is
		     present  in  stream  header).  Value is a string of three
		     characters	"xyz" which have the following meanings:
		      x: frame presentation
			 t - top-field-first
			 T - top-field-first and repeat
			 b - bottom-field-first
			 B - bottom-field-first	and repeat
			 1 - single progressive	frame
			 2 - double progressive	frame (repeat)
			 3 - triple progressive	frame (repeat)
		      y: frame temporal	sampling
			 p - progressive (fields sampled at same time)
			 i - interlaced	(fields	sampled	at different times)
		      z: frame chroma-subsampling
			 p - progressive (subsampling over whole frame)
			 i - interlaced	(each field subsampled independently)
			 ? - unknown (allowed only for non-4:2:0 subsampling)

	      X[string]	- 'metadata' (optional;	unparsed, but passed around)

       Note that a filter application must faithfully  forward	all  "X"  tags
       from  input  pipe  to output pipe (unless it uses one of	those tags, of
       course).	 The supplied library will do this automatically if the	 func-
       tions  y4m_copy_stream_info() and y4m_copy_frame_info() are used	appro-
       priately.

NOTES ON IMAGE DATA
       All image data is in the	CCIR-601 Y'CbCr	colorspace,  presented	plane-
       by-plane	 in  row-major	order.	 Each  sample within each plane	is one
       octet (8-bits) in size.	When all planes	are present, they  are	trans-
       mitted in the order Y', Cb, Cr, potentially followed by an alpha/trans-
       parency mask plane (for the 444alpha chroma format).  The alpha channel
       data  is	follows	the same range as the Y' luma channel:	full transpar-
       ency is at 16 and full opacity is at 235.

       All Y' and alpha	planes consist of (height X width) octets.   The  size
       of the chroma planes depends on the subsampling mode:

       -  4:4:4	- (height X width) octets

       -  4:2:2	- (height X width) / 2 octets

       -  4:1:1	- (height X width) / 4 octets

       -  4:2:0	- (height X width) / 4 octets

NOTES ON FRAMING
       (More to	come here.)

SEE ALSO
       mjpegtools(1), yuv4mpeg.h

AUTHOR
       This manual page	Copyright 2004 Matthew J. Marjanovic.

MJPEG Tools Team	       25 November 2002			   yuv4mpeg(5)

NAME | DESCRIPTION | GRAMMAR | NOTES ON IMAGE DATA | NOTES ON FRAMING | SEE ALSO | AUTHOR

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