Sound

[Gunther Hermann]

Hi

I read a few mails on vlc concerning sound, so maybe
my experiences interest you.

I'm currently running vlc 0.2.62 on SuSE 7.1 (i.e.
with 2.4p12 kernel, alsa and sdl installed). Vlc is
compiled from sources. My soundcard is a Creative
with Ensonique 1371 chip.

Concerning sound I observed the following quirks:
(1) Sound can be shaky (frequencies go up and down).
(2) Channel mixing fucked up
(3) Noise.

To (1):
this happened when I ran vlc with alsa sound drivers
loaded but not directing vlc to use its alsa plugin 
(i.e. it wrote to /dev/dsp instead), which you can on 
the command line (i.e. --aout alsa). 
Sound was OK when using the alsa plugin or when unloading
the alsa sound drivers and loading the kernel es1371
driver, then running vlc without plugin.

To (2):
when playing DVD's, right from the start I noticed that
all dialogues where bound to the right channel, so I
compared this against output from Aaron Holtzmann's original
ac3 decoder which was quite different. Playing around
with vlc sources I found out that downmixing in the frequency
domain is fucked (i.e. it doesn't work). One can hack the
source to get it right, but that doesn't solve the real
problem (there's an 'if(doable)..else..' statement in
ipmcd.c which you can hack to always use the else branch).

To (3):
when 'pumping up the volume' I noticed quite a noise, and
one of my DVD's with only 2 sound channels (Groundhog Day)
is hardly enjoyable because of the noise (I mean you can
understand everything, but the sound isn't pure). Again I 
compared to ac3dec where output was OK. Now on this I found 
out nothing, but I think vlc's ac3 decoder has a problem.
At least it experienced considerable reengineering compared
to Holtzmann sources, and maybe that introduced some bugs ??

Apart from the sound problems (and regular crashing at the
end of input with Xlib error), vlc is REALLY GREAT. It
plays DVD's like you expect it, video is brilliant and
all in sync (poor oms people who got still lots of work
to do, but hey they're only a few !!!). The source is well
documented and its straightforward to hack for that few
things which one may be missing (for example adding command
line parameter to choose a user defined title number when 
playing DVD, overriding the default '1' which is not always
correct).

For the first time I see a real chance of throwing windoze
ultimatively away. Many thanks for this
Gunther
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