mpeg2dec.doc

MPEG-2 has 7 distinct parts as well. The first part is the Systems section which defines the contain

                                 mpeg2decode
                                 ===========

                   MPEG-2 Video Decoder, Version 1.1, June 1994

                        MPEG Software Simulation Group
                             ([e-mail])



The program mpeg2decode is our implementation of an ISO/IEC DIS 13818-2
decoder. It converts MPEG-1 and MPEG-2 video bitstreams into uncompressed
video.


Features
========

+ decodes non-scalable, spatial scalable, SNR scalable and data partitioning
  MPEG-2 video bitstreams

+ supports Simple, Main, SNR Scalable and Spatially Scalable Profile streams
  at all defined levels

+ decodes MPEG-1 (ISO/IEC IS 11172-2) video bitstreams (except D-picture
  sequences)

+ several output formats: separate and interleaved Y,U,V component,
  Truevision TGA, PBMPLUS PPM, X11 display

+ 8 bit ordered dither and interlaced to progressive scan conversion
  for X11 display

+ optional output of detailed decoding information

+ robustness against stream syntax errors

+ fast IEEE 1180-1990 compliant integer arithmetic inverse DCT

+ optional double precision floating point inverse DCT


Missing Features
================

- spatial scalability other than interlaced -> interlaced

- D-picture MPEG-1 sequences

- temporal scalability

- error concealment

- repeat_field_first and other mostly display process oriented features


Introduction
============

mpeg2decode takes one or more ISO/IEC DIS 13818-2 [1] MPEG-2 video bitstreams
and converts them to uncompressed video. Since MPEG-2 is (by definition)
forward compatible with MPEG-1, mpeg2decode also decodes MPEG-1 sequences
(ISO/IEC IS 11172-2 [2]).

The decoder is not optimized for speed, although some parts (e.g. variable
length decoding, inverse DCT) are based on relatively fast algorithms. The
emphasis was on correct implementation of the standard and simple structure
of the program. Its main purpose is to demonstrate a sample implementation of
an MPEG-2 decoder and to serve as an educational tool. Our hope is that this
implementation makes it easier to understand the relatively complex details
of the standard.

As you can deduce from the list of missing features, mpeg2decode is still under
development. However, we considered the current version to be complete
enough to justify a public release.

The decoder has been extensively tested on bitstreams produced by a variety
of encoders from the MPEG research community to ascertain validity of the
implementation. Of course we can't guarantee complete compliance with the
standard.


Usage
=====

mpeg2decode {options} input.m2v {upper.m2v} {outfile}

Options:

-vn  verbose output (n: level)

Instructs mpeg2decode to generate informative ouput about the sequence
to stdout. Increasing level (-v1, -v2, etc.) results in more detailed
output.

-on  output format (0: YUV, 1: SIF, 2: TGA, 3:PPM, 4:X11, 5:X11 HiQ)

To choose a file format for the decoded pictures. Default is 0 (YUV).
The following formats are currently supported:

YUV: three headerless files, one for each component. The luminance component
     is stored with an extension of .Y, the chrominance components are
     stored as .U and .V respectively. Size of the chrominance files depends
     on the chroma_format used by the sequence. In case of 4:2:0 they have
     half resolution in both dimensions, in case of 4:2:2 they are subsampled
     in horizontal direction only, while 4:4:4 uses full chrominance
     resolution. All components are stored in row storage from top left to
     bottom right.

SIF: one headerless file, with interleaved components. Component order
     is Cb, Y, Cr, Y. This format is also known as Abekas or CCIR Rec. 656
     format. The chrominance components have half resolution in horizontal
     direction (4:2:2) and are aligned with the even luminance samples.
     File extension is .SIF.

TGA: Truevision TGA [4] 24 bit R,G,B format in uncompressed (no run length
     coding) format with .tga extension.

PPM: Portable PixMap format as defined in PBMPLUS [5], a graphics package by
     Jef Poskanzer. Extension is .ppm.

X11: display decoded video on an X Window System server. The current version
     supports only 8 bit color display. You can use the DISPLAY environment
     variable to select a (non-default) display. The output routines perform
     8 bit dithering and interlaced to progressive scan conversion. You can
     choose among two different scan conversion algorithms (only for 4:2:0
     interlaced streams):

     - a high quality slow algorithm (-o5, X11 HiQ)
     - a faster but less accurate algorithm (-o4, X11)

-f   store interlaced frames in frame format

By default, interlaced video is stored field by field. The -f option
permits to store both fields of a frame into one file.

-r   use double precision reference IDCT

The -r option selects a double precision inverse DCT which is primarily
useful for comparing results from different decoders. The default is to
use a faster integer arithmetic only IDCT implementation which meets the
criteria of IEEE 1180-1990 [3].

-s infile  spatial scalable sequence

Spatial scalable video is decoded in two passes. The -s option specifies
the names of the output files from the first (lower layer) pass to the
second (enhancement layer) pass. 'infile' describes the name format of the
lower layer pictures for spatial scalable sequences in a format similar to
outfile as described below.

-q

Set this switch to suppress output of warnings to stderr. Usually a bad idea.

-t

Setting this option activates low level tracing to stdout. This is mainly for
debugging purposes. Output is extremely voluminous. It currently doesn't
cover all syntactic elements.

outfile

This parameter has to be specified for output types -o0 to -o3 only. It
describes the names of the output files as a printf format string. It has to
contain exactly one integer format descriptor (e.g. %d, %02d) and, except
for frame storage (-f option or progressive video), a %c descriptor

example: out%02d_%c generates files

	out00_a.*, out00_b.*, out01_a.*, ...

	('a' denotes the top field, 'b' the bottom field,
	 .* is the suffix appropriate for the output format)


upper.m2v

is the name of the upper layer bitstream of an SNR scalable stream or a
data partioning scalable bitstream (input.m2v is the lower layer).


Examples
========

non-scalable stream (one layer, one pass):

	mpeg2decode base.m2v f%d%c

SNR-scalable stream (two layers, one pass):

	mpeg2decode base.m2v snr.m2v f%d%c

spatial-scalable stream (two layers, two passes):

	mpeg2decode base.m2v l%d%c
	mpeg2decode -s l%d%c spatial.m2v f%d%c

hybrid spatial/SNR-scalable stream (three layers, two passes):

	mpeg2decode base.m2v l%d%c
	mpeg2decode -s l%d%c spatial.m2v snr.m2v f%d%c

hybrid SNR/spatial-scalable stream (three layers, two passes):

	mpeg2decode base.m2v snr.m2v l%d%c
	mpeg2decode -s l%d%c spatial.m2v f%d%c

hybrid SNR/spatial/SNR-scalable stream (four layers, two passes):

	mpeg2decode base.m2v snr1.m2v l%d%c
	mpeg2decode -s l%d%c spatial.m2v snr2.m2v f%d%c

etc.


References
==========

[1] Draft International Standard ISO/IEC DIS 13818: Generic Coding of
    Moving Pictures and Associated Audio, Part 2: Video.

[2] International Standard ISO/IEC IS 11172: Coding of moving pictures
    and associated audio for digital storage media up to about 1,5 Mbit/s,
    Part 2: Video.

[3] IEEE Standard Specifications for the Implementations of 8 by 8
    Inverse Discrete Cosine Transform, IEEE Std 1180-1990, December 6, 1990.

[4] Truevision TGA (TM) File Format Specification Version 2.0, January 1991.

[5] Jef Poskanzer: PBMPLUS, Extended Portable Bitmap Toolkit, December 10, 1991.