I am having some issues getting audio timestamps when opening a device through dmix. When I open the hardware directly, e.g. "hw:0,0", I get all the timestamps and delay frames. However, when I open through dmix, e..g "dmix:0,0", the audio timestamps and delay frames are zero.
Below is a test application which illustrates this issue on my setup, it takes the ALSA device as its argument and I am linking against the latest stable alsa (1.0.29).
Any help with this would be much appreciated.
-Dan
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#include <asoundlib.h>
snd_pcm_t *handle;
int getFramesReady()
{
int framesReady = 0;
int error;
if ((error = snd_pcm_wait (handle, 100)) < 0) {
fprintf (stderr, "poll failed (%s)\n", strerror (errno));
return 0;
}
if ((framesReady = snd_pcm_avail_update (handle)) < 0) {
if (framesReady == -EPIPE) {
fprintf (stderr, "an xrun occured\n");
return 0;
} else {
fprintf (stderr, "unknown ALSA avail update return value (%d)\n",
framesReady);
return 0;
}
}
framesReady = framesReady > 4096 ? 4096 : framesReady;
return framesReady;
}
long timestamp2ns(snd_htimestamp_t t)
{
int64_t ns;
ns = t.tv_sec * 1000000000;
ns += t.tv_nsec;
return ns;
}
void printTimestamps()
{
int error;
snd_pcm_status_t *status;
snd_pcm_status_alloca(&status);
if ((error = snd_pcm_status(handle, status)) < 0) {
fprintf(stderr, "Stream status error: %s\n", snd_strerror(error));
exit(1);
}
snd_htimestamp_t temp_ts;
snd_pcm_status_get_htstamp(status, &temp_ts);
printf("host: %ld\n", timestamp2ns(temp_ts));
snd_pcm_status_get_audio_htstamp(status, &temp_ts);
printf("audio: %ld\n", timestamp2ns(temp_ts));
snd_pcm_status_get_trigger_htstamp(status, &temp_ts);
printf("trigger: %ld\n", timestamp2ns(temp_ts));
printf("avail: %u\n", snd_pcm_status_get_avail(status));
printf("delay: %u\n", snd_pcm_status_get_delay(status));
printf("--------------------------------------------\n");
}
int main(int argc, char *argv[])
{
char *deviceName;
int error;
snd_pcm_hw_params_t *hwParams;
snd_pcm_sw_params_t *swParams;
snd_pcm_hw_params_malloc(&hwParams);
snd_pcm_sw_params_malloc(&swParams);
if (argc != 2) {
printf("Needs alsa playback device name as input\n");
return 0;
}
deviceName = argv[1];
if ((error = snd_pcm_open(&handle, deviceName, SND_PCM_STREAM_PLAYBACK, SND_PCM_NO_AUTO_RESAMPLE)) < 0) {
printf("Alsa Device open error: %s\n", snd_strerror(error));
}
// hw
snd_pcm_hw_params_any(handle, hwParams);
if ((error = snd_pcm_hw_params_set_access (handle, hwParams, SND_PCM_ACCESS_RW_INTERLEAVED)) < 0) {
fprintf (stderr, "cannot set access type (%s)\n",
snd_strerror (error));
exit (1);
}
if ((error = snd_pcm_hw_params (handle, hwParams)) < 0) {
fprintf (stderr, "cannot set parameters (%s)\n",
snd_strerror (error));
exit (1);
}
// sw
if ((error = snd_pcm_sw_params_current (handle, swParams)) < 0) {
fprintf (stderr, "cannot initialize software parameters structure (%s)\n",
snd_strerror (error));
exit (1);
}
if ((error = snd_pcm_sw_params_set_avail_min (handle, swParams, 4096)) < 0) {
fprintf (stderr, "cannot set minimum available count (%s)\n",
snd_strerror (error));
exit (1);
}
if ((error = snd_pcm_sw_params_set_start_threshold (handle, swParams, 0U)) < 0) {
fprintf (stderr, "cannot set start mode (%s)\n",
snd_strerror (error));
exit (1);
}
if ((error = snd_pcm_sw_params_set_tstamp_mode(handle, swParams, SND_PCM_TSTAMP_ENABLE)) < 0) {
fprintf(stderr,"Unable to set tstamp mode : %s\n", snd_strerror(error));
exit(1);
}
// write sw params
if ((error = snd_pcm_sw_params (handle, swParams)) < 0) {
fprintf (stderr, "cannot set software parameters (%s)\n",
snd_strerror (error));
exit (1);
}
//start
if ((error = snd_pcm_prepare (handle)) < 0) {
fprintf (stderr, "cannot prepare audio interface for use (%s)\n",
snd_strerror (error));
exit (1);
}
char buf[102400] = {0};
while (1) {
usleep(100);
int32_t framesReady = getFramesReady();
if (framesReady) {
printTimestamps();
if ((error = snd_pcm_writei (handle, buf, framesReady)) < 0) {
fprintf (stderr, "write failed (%s)\n", snd_strerror (error));
}
}
}
}
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