AUDIO SYNC AND DXR3 CARDS FAQ

Version 1.1 4th November, 2002

Getting audio in sync with the dxr3 card can difficult.  The problem
is that the video decoding can take a different amount of time than
outputting the audio.

To start with, you need to understand how the dxr3 works with mplayer
and xine.  For MPEG 1 and 2 format video, the MPEG video data is sent
directly to the dxr3 card and decoded in hardware.  For other formats
of video, the video stream is decoded and then re-encoded as MPEG and
sent to the card.  This means for different types of video you will
get different delays in processing so the audio might run more or less
ahead of the video.

For this reason you may need to try different methods for different
video codec types and formats.

GENERAL

Here are some things to try to get your audio just right so that it
doesn't seem like you're watching a badly dubbed kung-fu movie.

* Make sure you're using the latest combination of dxr3 drivers and
  video player (xine or mplayer) as constant improvements are being
  made.

* Check that it's not the video file itself.  Many divx and other
  files found on the net can have poor sync internally.  Make sure
  you're working with good sources.  Try playing it to your computer
  screen (not through the dxr3) and see if that is in sync.

* Try all the different audio drivers.  I particularly find that the
  SDL driver can work better, which is odd but works.
  In mplayer: mplayer -ao <audio driver>

* If you're using your computer's sound card, try using the dxr3
  card's audio output instead.
  In mplayer: mplayer -ao oss:/dev/em8300_ma-0 (replace "0" with
  the number of dxr3 card you want to use.)

* If you're running some audio server like artsd (KDE) or esd (Gnome),
  try playing without that and taalking directly to the sound hardware
  instead.

* Your machine might have trouble keeping up, particularly playing
  non-MPEG video such as divx.  Try:
  In mplayer: mplayer -framedrop

* Newer versions of MPlayer have some special options for sync with
  the dxr3.  Try this for anything other than mpeg:
  In mplayer: mplayer -vo dxr3:prebuf:sync -vop lavc=1:29.97

  And for standard mpeg 1 or 2 (including DVDs):
  -vo dxr3:prebuf:sync

* Experiment with delays on the audio.  You should work with something
  very dialogue-based to test this.  An episode of the West Wing works
  well.  Again, make sure you're using a good video file.
  In mplayer: mplayer -delay <secs> (delay can be a floating point
  value)

AVI FILES

Some AVI files have peculiar problems with audio sync which can be
helped with the following options.

* Use a non-interleaved AVI parser.  Normally, audio and video are
  interleaved in the avi file, so you can read the file
  sequentially. For some broken avis, however, you need to read the
  audio and video stream separately. If you use this option and the
  file is badly interleaved, playing directly from a cd might be
  impossible, because your drive has to jump around a lot.  In these
  cases, you have to copy the file to your harddisk first.
  In mplayer: mplayer -ni

* Some AVI files have broken headers and this can be fixed.
  mplayer -nobps

* The audio can get seriously out of whack and to get it back in sync
  may require a more extreme correction than the default.  Setting the
  maximum correction to something like three seconds works well.
  mplayer -mc <number in seconds>

Finally, there are many, especially older avis out there (> 1.5 years)
that  have really fucked up a/v sync and even don't play right under
Windows.  If you get in contact with such a file, there's little you
can do but look for a better copy.

Maintained by Simon Rumble <simon.dxr3@rumble.net>
Thanks for the input from Michael Hunold <hunold-ml@web.de>.