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 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. 

 

 

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

• a52decX (http://homepage1.nifty.com/~toku/software_en.html) -

a graphical interface for a52dec in macintosh osX.

• bd4go (http://denisx.dyndns.org/bd4go/) - another graphical

interface for macintosh osX.

• 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 :) 

 

 

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 ! 

 

 

The A/52 standard, as published by the ATSC, is available at http://www.atsc.org/standards/a_52a.pdf 

 

 

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. 

 

 

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. 

 

 

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

 

 

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. 

 

 

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

 

 

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

 

Decoders