RepoMirrors/mpv
1
0
Fork 0
mirror of https://github.com/mpv-player/mpv synced 2024-12-24 15:52:25 +00:00
Code Issues Releases Wiki Activity

ao_alsa: handle --audio-stream-silence

Browse Source 
push.c does not handle this automatically, and AOs using push.c have to
handle it themselves. Also, ALSA is low-level enough that it needs
explicit support in user code. At least I haven't found any option that
does this.

We still can get away relatively cheaply by abusing underflow-handling
for this. ao_alsa.c already configures ALSA to handle underflows by
playing silence. So we purposely induce an underflow when opening the
device, as well as when pausing or resetting the device.

This introduces minor misbehavior: it doesn't account for the additional
delay the initial silence adds, unless the device has fully played the
fragment of silence when the player starts sending data to it. But
nobody cares.
This commit is contained in:
wm4 2016-08-09 16:35:33 +02:00
parent 062349ff5b
commit 2ded41d2be
1 changed files with 51 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

60
audio/out/ao_alsa.c
View File

@ -53,6 +53,7 @@ struct priv {
bool device_lost;
snd_pcm_format_t alsa_fmt;
bool can_pause;
bool pretend_pause;
snd_pcm_sframes_t prepause_frames;
double delay_before_pause;
snd_pcm_uframes_t buffersize;
@ -785,6 +786,14 @@ static int init_device(struct ao *ao, int mode)
MP_VERBOSE(ao, "buffersize: %d samples\n", (int)p->buffersize);
MP_VERBOSE(ao, "period size: %d samples\n", (int)p->outburst);
ao->device_buffer = p->buffersize;
// ao_alsa implements this by relying on underrun behavior (no data means
// underrun, during which silence is played). Trigger by playing some
// initial silence.
if (ao->stream_silence)
ao_play_silence(ao, p->outburst);
return 0;
alsa_error:
@ -874,7 +883,7 @@ static double get_delay(struct ao *ao)
struct priv *p = ao->priv;
snd_pcm_sframes_t delay;
if (snd_pcm_state(p->alsa) == SND_PCM_STATE_PAUSED)
if (snd_pcm_state(p->alsa) == SND_PCM_STATE_PAUSED || p->pretend_pause)
return p->delay_before_pause;
if (snd_pcm_delay(p->alsa, &delay) < 0)
@ -888,12 +897,34 @@ static double get_delay(struct ao *ao)
return delay / (double)ao->samplerate;
}
// For stream-silence mode: replace remaining buffer with silence.
// Tries to cause an instant buffer underrun.
static void soft_reset(struct ao *ao)
{
struct priv *p = ao->priv;
snd_pcm_sframes_t frames = snd_pcm_rewindable(p->alsa);
if (frames > 0 && snd_pcm_state(p->alsa) == SND_PCM_STATE_RUNNING) {
frames = snd_pcm_rewind(p->alsa, frames);
if (frames < 0) {
int err = frames;
CHECK_ALSA_WARN("pcm rewind error");
}
}
}
static void audio_pause(struct ao *ao)
{
struct priv *p = ao->priv;
int err;
if (p->can_pause) {
if (ao->stream_silence) {
if (snd_pcm_state(p->alsa) == SND_PCM_STATE_RUNNING) {
p->delay_before_pause = get_delay(ao);
p->prepause_frames = p->delay_before_pause * ao->samplerate;
soft_reset(ao);
p->pretend_pause = true;
}
} else if (p->can_pause) {
if (snd_pcm_state(p->alsa) == SND_PCM_STATE_RUNNING) {
p->delay_before_pause = get_delay(ao);
err = snd_pcm_pause(p->alsa, 1);
@ -932,7 +963,12 @@ static void audio_resume(struct ao *ao)
resume_device(ao);
if (p->can_pause) {
if (ao->stream_silence) {
p->pretend_pause = false;
get_delay(ao); // recovers from underrun (as a side-effect)
if (p->prepause_frames)
ao_play_silence(ao, p->prepause_frames);
} else if (p->can_pause) {
if (snd_pcm_state(p->alsa) == SND_PCM_STATE_PAUSED) {
err = snd_pcm_pause(p->alsa, 0);
CHECK_ALSA_ERROR("pcm resume error");
@ -953,12 +989,18 @@ static void reset(struct ao *ao)
struct priv *p = ao->priv;
int err;
p->prepause_frames = 0;
p->delay_before_pause = 0;
err = snd_pcm_drop(p->alsa);
CHECK_ALSA_ERROR("pcm prepare error");
err = snd_pcm_prepare(p->alsa);
CHECK_ALSA_ERROR("pcm prepare error");
p->pretend_pause = false;
if (ao->stream_silence) {
soft_reset(ao);
} else {
p->prepause_frames = 0;
p->delay_before_pause = 0;
err = snd_pcm_drop(p->alsa);
CHECK_ALSA_ERROR("pcm prepare error");
err = snd_pcm_prepare(p->alsa);
CHECK_ALSA_ERROR("pcm prepare error");
}
alsa_error: ;
}