

ABOUT LIBA52

liba52 is a free library for decoding ATSC A/52 streams. It is
released under the terms of the GPL license. The A/52 standard is used
in a variety of applications, including digital television and DVD. It
is also known as AC-3.

The main goals in liba52 development are:

      *	Portability - Currently all of the code is written in C, and
	when we write platform-specific optimizations we will always
	keep a generic C routine to fall back on.

      *	Reuseability - we do not want liba52 to include any
	project-specific code, but it should still include enough
	features to be used by very diverse projects.

      *	Precision - We are trying to implement all of the A/52
	standard, and to have a very precise output by doing all the
	calculations in floating point. We have a test suite that
	detects any deviation in the output when compared to previous
	versions. We do not have access to official A/52 test vectors
	though, so we have to use our judgement to ensure that such
	deviations are only intruduced when we fix bugs !

      *	Speed - liba52 is really fast, on any modern PC it should take
	only a few percent of CPU time.

The project homepage is at http://liba52.sourceforge.net/


A52DEC

a52dec is a test program for liba52. It decodes ATSC A/52 streams, and
also includes a demultiplexer for mpeg-1 and mpeg-2 program streams.

The liba52 source code is always distributed in the a52dec package, to
make sure it easier for people to test it.

The basic usage is to just type "a52dec file" where file is an ATSC
A/52 file.

The "-s" option must be used for multiplexed (audio and video) mpeg-2
files. These files are usualy found on the internet or on unencrypted
DVDs.

The "-o" option is used to select a given output layer. By default
a52dec does a stereo downmix and outputs to your speakers, but you can
try other choices using this option. This is also used for performance
testing and conformance testing.

The "-c" option is used to disable all optimizations (currently only djbfft).

The "-r" option is used to disable the dynamic range compression.


OTHER PROJECTS USING LIBA52

liba52 (and its ancestor libac3) is being used by various other
projects, including:

      *	xine (http://xine.sourceforge.net/) - started as a simple
	mpeg-2 audio and video decoder, but it since became a
	full-featured DVD and video media player.

      *	MPlayer (http://www.MPlayerHQ.hu) - another good player, it is
	also very robust against damaged streams.

      *	movietime (http://movietime.sourceforge.net/) - still quite
	young, but it looks very promising !

      *	ffmpeg (http://ffmpeg.sourceforge.net/) - a nice audio/video
	encoder and transcoder, uses liba52 for decoding A/52 streams.

      *	Ogle (http://www.dtek.chalmers.se/groups/dvd/) - a good DVD
	player with menu support

      *	OMS (http://www.linuxvideo.org/oms/)

      *	XMPS (http://xmps.sourceforge.net/)

      *	GStreamer (http://www.gstreamer.net/) - a framework for
	streaming media; it has an A/52 decoding plugin based on liba52.

      *	mpeglib (http://mpeglib.sourceforge.net/) - a video decoding
	library that usess liba52 when decoding A/52 streams.

If you use liba52 in another project, let us know !

VideoLAN (http://www.videolan.org/) does not use liba52, but this is
still a cool project :)


TASKS

There are several places where we could easily use some help:

      *	Web design: This site sucks ! at the very least, we'd like to
	come up with a nicer background picture and a logo.

      *	Testing: If you find any stream that does not decode right
	with liba52, let us know ! The best thing would be to mail to
	the liba52-devel mailing list. Also if you have access to
	encoders, we'd love to get test streams that would be free of
	rights - so that we can put them on this server.

      *	Coding: you can have a look in the TODO file first ! The most
	important item is probably to make the code fully reentrant.

      *	Porting: If you're porting to a new architecture, you might
	want to experiment with the compile flags defined in
	configure.in . When you figure out whats fastest on your
	platform, send us a patch !


REFERENCES

The A/52 standard is publically available at these locations:

      *	http://www.atsc.org/standards/a_52a.pdf - The main part of the
	standard, as published by the ATSC.

      *	http://www.dolby.com/tech/ATSC_err.pdf - A list of erratas in
	the ATSC standard, published by Dolby. It applies to the
	previous revision of the standard (A/52 not A/52a), but some
	erratas have not been fixed in the updated standard yet !


CVS SNAPSHOTS

A daily snapshot is created using "make distcheck" every night and
uploaded to http://liba52.sourceforge.net/files/a52dec-snapshot.tar.gz .
It is easier to use than the CVS repository, because you do not need
to have the right versions of automake, autoconf and libtool
installed. It might be convenient when working on a liba52 port for
example.


CVS REPOSITORY

The latest liba52 and a52dec source code can always be found by
anonymous CVS:

# export CVSROOT=:pserver:anonymous@cvs.liba52.sourceforge.net:/cvsroot/liba52
# cvs login (Just press Return when prompted for a password)
# cvs checkout a52dec

You can also browse the latest changes online at
http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/liba52/a52dec/

The other CVS modules are ac3dec-livid for the CVS history of the
project while it was still hosted on the linuxvideo.org servers, and
ac3dec for the CVS history of the project while the linuxvideo.org
servers were down and before the library switched its name to liba52.


MAILING LISTS

See the subscription information at http://liba52.sourceforge.net/lists.html

liba52-devel

This is the main mailing list for technical discussion about
liba52. Anyone wanting to work on liba52, or maybe just stay informed
about the development process, should probably subscribe to this list.

liba52-checkins

All liba52 checkins are announced there. This is a good way to keep
track of what goes into CVS.

liba52-announce

This is a very low traffic mailing list, only for announcements of new
versions of liba52. Only project administrators can post there.
