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Re: [livid-dev] audio bug

On Sat, Feb 03, 2001 at 04:47:57PM -0500, Andrew Molloy wrote:
> I think I have found a problem with the audio.  It appears that 48KHz
> audio is being played as 44.1KHz.  I'm watching "The Matrix" and its
> average framerate is exactly 22.05 fps.  The audio plays at a lower
> pitch than it should and it is slightly too slow, but it does not skip
> at all.  To support my claim note that 22.05 fps / 24 fps == 44.1KHz /
> 48 KHz.  I have checked in Windows and the DVD is in fact using 48KHz
> audio.  With audio set to null, I get ~45 fps with SDL and ~65 fps with
> X11.  Dual PIII 600MHz, Nvidia GeForce2 Ultra, Soundblaster Vibra 16XV
> (aka Soundblaster 16), X 4.0.2

That's because the SB16-based (EMU-8xxx) cards are limited to 16-bit,
44100-khz output (CD-rates).  The newer cards with SB Live (EMU10k-based)
engines operate at 48000 khz sampling rate max.

I have an AWE64 card myself, so I know the symptoms quite well, and it occurs
with all the A/V apps I've tried under linux.  There are two solutions:

1)  Get a modern soundcard that supports 48k :) But I'm cheap, so haven't
done that yet.

2)  Do software downsampling- CPU intensive, trade-off between CPU usage
and interpolation quality.  I was considering doing this myself, but
got distracted by my TV-card.  If the audio decoding is done as a separate
thread (I think it is), it should be fine on my dual 550 or your dual 600 
(oms barely touches my 2nd cpu), but may increase the single cpu hw 
requirements.  There are downsampling routines in sox, but you can't just 
pipe it to sox and expect much in the way of synch.

R C