[vlc-devel] Re: vlc sound playback breaks for USB between ALSA 1.0.9b and 1.0.10rc2

[Benjamin Pracht]

On Mon, Oct 31, 2005, Matthew Hodgson wrote :
> Hi all,
> 
> I spent a while wrestling with getting audio playback to work with my 
> M-Audio Transit USB soundcard today - when playing back 44.1kHz or 48kHz 
> sound with ALSA ~1.0.10rc2 I was getting:
> 
> [00000838] main audio output debug: audio output is starving (35064), 
> playing silence
> [00000838] alsa audio output warning: recovered from buffer underrun
> [00000838] main audio output debug: audio output is starving (32402), 
> playing silence
> [00000838] alsa audio output warning: recovered from buffer underrun
> [00000838] main audio output debug: audio output is starving (41727), 
> playing silence
> [00000838] alsa audio output warning: recovered from buffer underrun
> 
> with --aout alsa and similar for --aout oss.  The timestamp diff in the 
> starvation warning message is consistently ~40ms, and no sound was output.
> 
> VLC does however play back 22kHz files correctly (and at the right pitch).
> 
> I've reported this to the ALSA list 
> (http://article.gmane.org/gmane.linux.alsa.user/20764), as the problem 
> didn't happen with 1.0.9b - but as aplay and mplayer behave fine, i think a 
> problem may hhave been exposed in VLC's aout code with the more recent 
> ALSA. This happens with all VLCs from at least 0.8.1 through to today's 
>  svn.
> 
> Any thoughts would be very much appreciated (and thanks again to those on 
> IRC who gave assistance earlier :)
> 

Well, mplayer sends 16 bits samples to the soundcard by default, AFAIK,
VLC 32 bits samples. That may explain the difference...

I cannot see any easy way to force VLC to send 16 bits samples to the
soundcard without patching the code...

On recent svn, using the --aout-rate 44001 option with alsa should have
this side effect, but the use of a non standard rate may cause other
issues. Could you please try however and see it that makes any change ?

-- 
BigBen

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