liba52 - a free ATSC A/52 stream decoder

News

July 27, 2002: a52dec-0.7.4 is released ! With full reentrancy, win32 output, al file output, gain control, and a few portability fixes.

February 20, 2002: a52dec-0.7.3 is released ! With 40% to 80% improved speed, some bugfixes, and a few new output modules.

December 16, 2001: a52dec-0.7.2 is released ! This release adds wav format output, and an improved demuxer which makes it easier to use a52dec as a pipe. Also, lots of minor bugfixes and performance/portability enhancements.

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.

Other projects using liba52

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

• xine - started as a simple mpeg-2 audio and video decoder, but it since became a full-featured DVD and video media player.
• VideoLAN - video streaming over an ethernet network, can also be used as a standalone player.
• MPlayer - another good player, it is also very robust against damaged streams.
• movietime - still quite young, but it looks very promising !
• ffmpeg - a nice audio/video encoder and transcoder, uses liba52 for decoding A/52 streams.
• Ogle - a good DVD player with menu support.
• TCVP - video and music player for unix.
• a52decX - a graphical interface for a52dec for macintosh osX.
• bd4go - another graphical interface for macintosh osX.
• drip - a DVD to DIVX transcoder.
• OMS
• XMPS
• GStreamer - a framework for streaming media; it has an A/52 decoding plugin based on liba52.
• mpeglib - a video decoding library that usess liba52 when decoding A/52 streams.

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

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: There is a small TODO list in the a52dec package, you can have a look there !
• 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, as published by the ATSC, is available at http://www.atsc.org/standards/a_52a.pdf