181 lines
6.1 KiB
Text
181 lines
6.1 KiB
Text
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ABOUT LIBA52
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liba52 is a free library for decoding ATSC A/52 streams. It is
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released under the terms of the GPL license. The A/52 standard is used
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in a variety of applications, including digital television and DVD. It
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is also known as AC-3.
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The main goals in liba52 development are:
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* Portability - Currently all of the code is written in C, and
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when we write platform-specific optimizations we will always
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keep a generic C routine to fall back on.
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* Reuseability - we do not want liba52 to include any
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project-specific code, but it should still include enough
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features to be used by very diverse projects.
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* Precision - We are trying to implement all of the A/52
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standard, and to have a very precise output by doing all the
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calculations in floating point. We have a test suite that
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detects any deviation in the output when compared to previous
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versions. We do not have access to official A/52 test vectors
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though, so we have to use our judgement to ensure that such
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deviations are only intruduced when we fix bugs !
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* Speed - liba52 is really fast, on any modern PC it should take
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only a few percent of CPU time.
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The project homepage is at http://liba52.sourceforge.net/
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A52DEC
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a52dec is a test program for liba52. It decodes ATSC A/52 streams, and
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also includes a demultiplexer for mpeg-1 and mpeg-2 program streams.
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The liba52 source code is always distributed in the a52dec package, to
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make sure it easier for people to test it.
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The basic usage is to just type "a52dec file" where file is an ATSC
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A/52 file.
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The "-s" option must be used for multiplexed (audio and video) mpeg-2
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files. These files are usualy found on the internet or on unencrypted
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DVDs.
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The "-o" option is used to select a given output layer. By default
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a52dec does a stereo downmix and outputs to your speakers, but you can
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try other choices using this option. This is also used for performance
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testing and conformance testing.
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The "-c" option is used to disable all optimizations (currently only djbfft).
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The "-r" option is used to disable the dynamic range compression.
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OTHER PROJECTS USING LIBA52
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liba52 (and its ancestor libac3) is being used by various other
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projects, including:
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* xine (http://xine.sourceforge.net/) - started as a simple
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mpeg-2 audio and video decoder, but it since became a
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full-featured DVD and video media player.
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* VideoLAN (http://www.videolan.org/) - video streaming over an
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ethernet network, can also be used as a standalone player.
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* MPlayer (http://www.MPlayerHQ.hu) - another good player, it is
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also very robust against damaged streams.
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* movietime (http://movietime.sourceforge.net/) - still quite
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young, but it looks very promising !
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* ffmpeg (http://ffmpeg.sourceforge.net/) - a nice audio/video
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encoder and transcoder, uses liba52 for decoding A/52 streams.
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* Ogle (http://www.dtek.chalmers.se/groups/dvd/) - a good DVD
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player with menu support
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* a52decX (http://homepage1.nifty.com/~toku/software_en.html) -
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a graphical interface for a52dec in macintosh osX.
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* TCVP (http://tcvp.sf.net) - video and music player for unix.
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* bd4go (http://denisx.dyndns.org/bd4go/) - another graphical
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interface for macintosh osX.
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* drip (http://drip.sourceforge.net/) - a DVD to DIVX transcoder.
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* OMS (http://www.linuxvideo.org/oms/)
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* XMPS (http://xmps.sourceforge.net/)
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* GStreamer (http://www.gstreamer.net/) - a framework for
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streaming media; it has an A/52 decoding plugin based on liba52.
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* mpeglib (http://mpeglib.sourceforge.net/) - a video decoding
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library that usess liba52 when decoding A/52 streams.
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If you use liba52 in another project, let us know !
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TASKS
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There are several places where we could easily use some help:
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* Web design: This site sucks ! at the very least, we'd like to
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come up with a nicer background picture and a logo.
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* Testing: If you find any stream that does not decode right
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with liba52, let us know ! The best thing would be to mail to
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the liba52-devel mailing list. Also if you have access to
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encoders, we'd love to get test streams that would be free of
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rights - so that we can put them on this server.
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* Coding: you can have a look in the TODO file first ! The most
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important item is probably to make the code fully reentrant.
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* Porting: If you're porting to a new architecture, you might
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want to experiment with the compile flags defined in
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configure.in . When you figure out whats fastest on your
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platform, send us a patch !
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REFERENCES
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The A/52 standard, as published by the ATSC, is available at
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http://www.atsc.org/standards/a_52a.pdf
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CVS SNAPSHOTS
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A daily snapshot is created using "make distcheck" every night and
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uploaded to http://liba52.sourceforge.net/files/a52dec-snapshot.tar.gz .
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It is easier to use than the CVS repository, because you do not need
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to have the right versions of automake, autoconf and libtool
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installed. It might be convenient when working on a liba52 port for
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example.
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CVS REPOSITORY
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The latest liba52 and a52dec source code can always be found by
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anonymous CVS:
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# export CVSROOT=:pserver:anonymous@cvs.liba52.sourceforge.net:/cvsroot/liba52
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# cvs login (Just press Return when prompted for a password)
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# cvs checkout a52dec
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You can also browse the latest changes online at
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http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/liba52/a52dec/
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The other CVS modules are ac3dec-livid for the CVS history of the
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project while it was still hosted on the linuxvideo.org servers, and
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ac3dec for the CVS history of the project while the linuxvideo.org
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servers were down and before the library switched its name to liba52.
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MAILING LISTS
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See the subscription information at http://liba52.sourceforge.net/lists.html
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liba52-devel
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This is the main mailing list for technical discussion about
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liba52. Anyone wanting to work on liba52, or maybe just stay informed
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about the development process, should probably subscribe to this list.
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liba52-checkins
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All liba52 checkins are announced there. This is a good way to keep
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track of what goes into CVS.
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liba52-announce
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This is a very low traffic mailing list, only for announcements of new
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versions of liba52. Only project administrators can post there.
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