[MPlayer-users] Channel swapping with sotware AC3 decoding (CM8738)

Stefan Lange hoirkman at gmx.de
Thu Feb 27 01:03:53 CET 2003

Hi there!
A long time ago I already reported a bug concerning channel swapping 
during playback of 6-channel sound with a cmedia 8738 soundcard, using 
software AC3 decoding and analog output, which was fixed soon after (see 
for example)

I realized that channel-swapping still occurs however in certain 
situations. The symptoms are the same as they used to be in the old 
report: channels get swapped (center-content is output from rear-left 
for example). Pausing and unpausing again can be used to re-correct the 
channel setup.

The bug is triggered when there is heavy ide io-traffic while playing 
back a file, which results in mplayer getting stuck for little while. 
After it resumes playing, channels will be swapped. I assume that it 
happens when mplayer's file cache runs empty during playback. Increasing 
the -cache size to a large value is a workaround for the problem, as far 
as I could test. I don't really know whether this is a sound-driver bug, 
or a bug in mplayer, but maybe it can be fixed.

Brief system info (detailed info in attachment):

Distro: debian unstable
mplayer: cvs from a few minutes ago
linux-2.4.20, Athlon XP 1800+, Radeon 8500 graphics card, C-Media 8738 
soundcard, using kernel oss driver (using -ao oss with mplayer)


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