Underrun

Underrun

[Irfan Shaikh]

Hello All,

A)     I am getting many under-run in my audio capture and playback application.

         1) My CAPTURE buffer is of 1024 * 8 (Period size * no of periods), PLAYBACK buffer is of (512 * 16)
         2) I try to read 8 K frames each time and write returned frames to playback device.
         3) Stereo audio, sample size 2 bytes, frame size 4 bytes, 48000 Hz

I have done following to reduce under run :
         1) Increased the number of periods on playback device (to increase playback latency).
         2) optimized my code

Please sugest me some more way so that i can avoid underrun of my playback device


B) Can i use snd_pcm_prepare() twice in two consecutive lines

For eg :
{
snd_pcm_prepare(pcm);
 snd_pcm_prepare(pcm);
}

        I just want to know if this is OK for playback device state.

Regards




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Re: Underrun

[Clemens Ladisch]

Irfan Shaikh wrote:
> I am getting many under-run in my audio capture and playback application.
> 
> 1) My CAPTURE buffer is of 1024 * 8 (Period size * no of periods), PLAYBACK buffer is of (512 * 16)
> 2) I try to read 8 K frames each time and write returned frames to playback device.

If you wait until the capture buffer is full, it's likely that you
get over/underruns at this moment.  You have to do the processing in
smaller chunks.

Typically, in loops like this, the normal state is that the capture
buffer is almost empty, and the playback buffer almost full.  You read
one period from the capture buffer (waiting for it if necessary),
process it, and write it to the playback buffer.  You need at least two
period per buffer so that one can be captured/played while the other one
is being processed, and maybe more periods as safety against delays.

> B) Can i use snd_pcm_prepare() twice in two consecutive lines

Yes (if the driver isn't buggy).

Regards,
Clemens


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