Hey,
Op 20-04-11 15:18, David Henningsson schreef:
However if I
force underruns to occur,the state will stay running and it appears
there is still some data left in the buffer, so sound stalls entirely.
This is nothing I've heard of.
Sadly all too common here, if I feed data and it underruns, it may
appear to be running but is stalled entirely.
Could you provide a test case where this occurs? (Pulseaudio/ALSA
version, client applications/libraries, etc)
Well this could be a basic test version I suppose, although it's not
fair since it's guaranteed to underrun and doesn't work with dmix since
it specifies period sizes exactly.
Digging it up I can only
assume it's a bug in src/stream.c , but I haven't figured out why yet.
Tested with pulseaudio.c
2. Any comments on this patch for alsa-plugins?
IIRC, by setting handle_underrun to 1, you're reopening bugs of
broken/skipping audio for mpg123 and other programs, which get stuck in
an infinite loop of "write one sample, force start the stream, write
more samples, asynchronusly get an underrun, drop the stream and drop
samples already written".
There should be threads on at least alsa-devel about this, from a year
back or so.
This is exactly what my patch was addressing, I was fixing that bug by
handling underrun correctly. snd_pcm_prepare() is called when an
underrun occurs, so instead I make it only restart the stream if
underrun. Not handling underruns at all seems to allow it to stall on
xrun, while claiming to be running. This sometimes appears to happen in
other programs too though, like mplayer. Could it be because of the
weird latency value?
Ok, thanks for the clarifications. I've taken a closer look at your
patch now and have the following comments:
When you're calling pulse_start instead of continuing in pulse_prepare -
pulse_start will call uncork/trigger, won't that just cause another
underrun? Would it perhaps be better to just return without doing anything?
mpg123 was used as a test case for the original bug, and mpg123 calls
snd_pcm_drop on an underrun, so you will be regressing mpg123 by
changing handle_underrun to 1. (Now of course we could fix mpg123, but I
don't know if there are a lot of other programs out there doing similar
things?)
My main point is that the underrun is often obsolete when the message
reached the application, because more data has already been written,
therefore reporting it to the app does more harm than good.
At least until the underrun callback (and PA protocol) supports sending
the position of underrun, together with the underrun message. If we had
that position, we could compare that with the current write pointer to
determine whether the underrun is actually obsolete or not.
Well, this is a dumb unfair test program that forcibly underruns,
probably should work if you change default to hw:0, but I think dmix
doesn't allow you to set random period sizes. If I try this with the
pulseaudio default plugin, it will break.
With my patch:
~$ ./a.out
Written: 2047 - available: 2047
Successfully underrun
Written: 960 - available: 960
Successfully underrun
Written: 1890 - available: 1890
Successfully underrun
Without:
~$ ./a.out 2>/dev/null
Written: 2047 - available: 2047
Written: 0 - available: 0
Written: 0 - available: 0
Note: not any form of error checking is done here, just cobbled this
dumb program together for demonstration purposes. :)
Cheers,
Maarten
#include <stdio.h>
#include <unistd.h>
#include <asoundlib.h>
int main() {
unsigned t = 10000, rate = 44100;
char silence[4096] = {};
snd_pcm_hw_params_t *hw_parms;
snd_pcm_sw_params_t *sw_parms;
snd_pcm_t *pcm;
snd_pcm_hw_params_alloca(&hw_parms);
snd_pcm_sw_params_alloca(&sw_parms);
if (snd_pcm_open(&pcm, "default", SND_PCM_STREAM_PLAYBACK, SND_PCM_NONBLOCK) < 0) return 1;
snd_pcm_hw_params_any(pcm, hw_parms);
snd_pcm_hw_params_set_period_size(pcm, hw_parms, 512, 0);
snd_pcm_hw_params_set_periods(pcm, hw_parms, 4, 0);
snd_pcm_hw_params_set_format(pcm, hw_parms, SND_PCM_FORMAT_S16_LE);
snd_pcm_hw_params_set_rate_near(pcm, hw_parms, &rate, NULL);
snd_pcm_hw_params_set_channels(pcm, hw_parms, 1);
snd_pcm_hw_params_set_access(pcm, hw_parms, SND_PCM_ACCESS_RW_INTERLEAVED);
snd_pcm_hw_params(pcm, hw_parms);
snd_pcm_prepare(pcm);
snd_pcm_start(pcm);
snd_pcm_writei(pcm, silence, sizeof(silence)/2);
while (1) {
snd_pcm_uframes_t avail = snd_pcm_avail_update(pcm);
int state = snd_pcm_state(pcm);
if (state == SND_PCM_STATE_XRUN) {
printf("Successfully underrun\n");
avail = sizeof(silence)/2;
snd_pcm_prepare(pcm);
snd_pcm_writei(pcm, silence, avail);
} else if (state == SND_PCM_STATE_RUNNING) {
long ret = snd_pcm_writei(pcm, silence, avail);
printf("Written: %li - available: %lu\n", ret, avail);
usleep(100000);
}
usleep(10000);
}
}
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