[vlc-devel] ALSA problems

Rémi Denis-Courmont remi at remlab.net
Wed Jul 21 13:15:38 CEST 2010


For several years, there have been reports that VLC outputs choppy sound
with ALSA. Last week end, I managed to reliably trigger the problem. I
simply had to select an explicit ALSA device as output (i.e. vlc
--alsa-audio-device hw:0,0), and the audio sample rate is 44100 Hz.
Interestingly, if I leave the default, the sound is fine. Also, if I force
the output to 48kHz with --aout-rate 48000, the sound is fine. I get the
same problem with both "hw:0,0" and "plughw:0,0".

I am using an Intel ICH6 audio card. This was quite common a few years ago,
and should be similar to many other Intel motherboards.

I suppose ALSA automatically resamples to 48kHz when the "default" output
is used, otherwise I cannot explain this. I could not figure out the timing
logic in the ALSAFill function from our ALSA plugin.  The alsa-lib
documentation is not exactly great either. So I have been unable to address
this issue. I don't even know if it is a hardware, driver, ALSA-lib, or VLC

IOW, help is needed.

Rémi Denis-Courmont

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