Thanks, Trent, I've been playing a bit with snd_pcm_drain, snd_pcm_writei, blocking mode, non-blocking mode, etc. but even if I fill a full last period, audio does not play from the beginning to end unless I call snd_pcm_drain just before closing the stream. I think there is some concept that I'm missing about how ALSA works, or maybe my driver/ALSA configuration is broken (I'm using Arch Linux).
Do you have a brief example of playing a short WAV file using ALSA?
On Tue, Nov 13, 2012 at 5:45 AM, Trent Piepho tpiepho@gmail.com wrote:
snd_pcm_drain() will drain all the pending periods. In effect, it rounds up however many frames are left in the buffer to the next whole period. There is no way to just drain a partially full period.
If you always wrote full periods, and didn't use non-blocking mode so that each writei call always wrote everything before returning, then you shouldn't have a partially filled period at the end of the buffer.
ALSA has the exact buffer pointer value of the app pointer and also when a period should elapse, and could easily tell you the buffer fill value mod period size, but I don't think there is any API for that.
On Mon, Nov 12, 2012 at 7:15 PM, Daniel Sanz daniellsanz2@gmail.com wrote:
Can I expect that there won't be any pending frames (so no need to call snd_pcm_drain) if I always use snd_pcm_writei to write multiples of the period size?
And what if the sound is very short or the period size is big? the latency of hardware is negligible?
Thanks,
On Mon, Nov 12, 2012 at 9:57 PM, Trent Piepho tpiepho@gmail.com wrote:
You do have to fill to a full period before calling drain, or it won't work in a very useful way. It only stops when periods elapse. So if you have a half full period of audio at the end of the buffer you'll get garbage when it plays to the end of that period before stopping.
On Mon, Nov 12, 2012 at 2:36 AM, Clemens Ladisch clemens@ladisch.de wrote:
Enno Fennema wrote:
I want to close the pcm AFTER the sound finished.
Then close it after snd_pcm_drain() has returned.
The docs say calling drain() puts the pcm in the DRAINING state.
It also waits until the device has drained (unless the device is in non-blocking mode).
When I obtain the state immediately after drain() it is already SETUP. I hoped a state change from DRAINING to SETUP would be the right time to close the pcm but there appears to be no such state change.
That change happens immediately before snd_pcm_drain() returns.
Regards, Clemens _______________________________________________ Alsa-devel mailing list Alsa-devel@alsa-project.org http://mailman.alsa-project.org/mailman/listinfo/alsa-devel