3bd167771d
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@5970 a1c6a512-1295-4272-9138-f99709370657
180 lines
6.1 KiB
Text
180 lines
6.1 KiB
Text
|
|
|
|
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.
|
|
|
|
* VideoLAN (http://www.videolan.org/) - video streaming over an
|
|
ethernet network, can also be used as a standalone 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.
|
|
|
|
* TCVP (http://tcvp.sf.net) - video and music player for unix.
|
|
|
|
* bd4go (http://denisx.dyndns.org/bd4go/) - another graphical
|
|
interface for macintosh osX.
|
|
|
|
* drip (http://drip.sourceforge.net/) - a DVD to DIVX transcoder.
|
|
|
|
* 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 !
|
|
|
|
|
|
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, as published by the ATSC, is available at
|
|
http://www.atsc.org/standards/a_52a.pdf
|
|
|
|
|
|
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.
|