On Thu, 17 Jul 2003, Chris Raphael wrote:
> Thanks to the many people who have helped with my earlier questions.
>
> I am working on an application that simultaneously collects and plays
> sound. About 4 out of 5 times the program runs fine, but occasionally
> I have a problem with the input audio and output audio drifting apart.
> This seems to happen when I get playing underruns, although not all
> underruns seem to affect the synchronization. It isn't possible for
> me to completely avoid underruns, because my application can only
> compute the output audio about 20 ms before it is actually played.
>
> What I would like is for the audio driver to plays sample from the ring buffer in
> a circular manner, *whether or not there is an underrun*. That is,
> if there is an underrun, I would like the driver to continue writing
> samples in a circular fashion, even though some of them are garbage.
> In the event of an underrun, I don't care what is played before
> my application supplies the driver with audio data. But when the
> driver gets the audio I would like it to put it in the appropriate
> place in the ring buffer even though some garbage samples are *substituted*
> for my audio data.
>
> Put another way, I would like the driver to ignore underruns and simply
> allow the start and end pointers to cross over one another.
>
> Is this possible (or clear)?
Why not? Simply set start_threshold from sw_params to boundary wrapper
value. The nice example code is in alsa-lib/src/pcm/pcm_direct.c - look
for snd_pcm_sw_params_get_boundary() and lines around it.
A side note: You might move the read pointer (capture) manually
via the snd_pcm_forward() function to replace the garbage with silence or
something better (in case of underrun of course).
Jaroslav
-----
Jaroslav Kysela <[EMAIL PROTECTED]>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs
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