output/alsa: don't generate silence if ALSA-PCM buffer has enough data
If our `ring_buffer` is smaller than the ALSA-PCM buffer (if the
latter has more than the 4 periods we allocate), it can happen that
the start threshold is crossed and ALSA switches to
`SND_PCM_STATE_RUNNING`, but the `ring_buffer` is empty. In this
case, MPDD will generate silence, even though the ALSA-PCM buffer has
enough data. This causes stuttering (#420).
This commit amends an older workaround for a similar problem (commit
e08598e7e2
) by adding a snd_pcm_avail()
check, and only generate silence if there is less than one period of
data in the ALSA-PCM buffer.
Fixes #420
This commit is contained in:
parent
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NEWS
1
NEWS
@ -1,6 +1,7 @@
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ver 0.21.3 (not yet released)
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* output
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- alsa: fix crash bug
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- alsa: fix stuttering at start of playback
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ver 0.21.2 (2018/11/12)
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* protocol
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@ -109,6 +109,13 @@ class AlsaOutput final
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*/
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snd_pcm_uframes_t period_frames;
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/**
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* If snd_pcm_avail() goes above this value and no more data
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* is available in the #ring_buffer, we need to play some
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* silence.
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*/
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snd_pcm_sframes_t max_avail_frames;
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/**
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* Is this a buggy alsa-lib version, which needs a workaround
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* for the snd_pcm_drain() bug always returning -EAGAIN? See
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@ -482,6 +489,10 @@ AlsaOutput::Setup(AudioFormat &audio_format,
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period_frames = alsa_period_size;
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/* generate silence if there's less than once period of data
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in the ALSA-PCM buffer */
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max_avail_frames = hw_result.buffer_size - hw_result.period_size;
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silence = new uint8_t[snd_pcm_frames_to_bytes(pcm, alsa_period_size)];
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snd_pcm_format_set_silence(hw_result.format, silence,
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alsa_period_size * audio_format.channels);
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@ -933,7 +944,8 @@ try {
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CopyRingToPeriodBuffer();
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if (period_buffer.IsEmpty()) {
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if (snd_pcm_state(pcm) == SND_PCM_STATE_PREPARED) {
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if (snd_pcm_state(pcm) == SND_PCM_STATE_PREPARED ||
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snd_pcm_avail(pcm) <= max_avail_frames) {
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/* at SND_PCM_STATE_PREPARED (not yet switched
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to SND_PCM_STATE_RUNNING), we have no
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pressure to fill the ALSA buffer, because
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@ -943,6 +955,11 @@ try {
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monitoring the ALSA file descriptor, and
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let it be reactivated by Play()/Activate()
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whenever more data arrives */
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/* the same applies when there is still enough
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data in the ALSA-PCM buffer (determined by
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snd_pcm_avail()); this can happend at the
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start of playback, when our ring_buffer is
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smaller than the ALSA-PCM buffer */
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{
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const std::lock_guard<Mutex> lock(mutex);
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