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Constrain ALSA buffer size and start_threshold in fallback path #1703

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Constrain ALSA buffer size and start_threshold in fallback path #1703

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11 changes: 10 additions & 1 deletion playback/src/audio_backend/alsa.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -362,6 +362,11 @@ fn open_device(dev_name: &str, format: AudioFormat) -> SinkResult<(PCM, usize)>

trace!("You may experience higher than normal CPU usage and/or audio issues.");

// Still try to constrain the buffer size. Some devices default to
// very large buffers (e.g. 1M+ frames) which delays playback start
// (due to start_threshold) and blocks track changes (due to drain).
let _ = hwp_clone.set_buffer_size_near(MAX_BUFFER);

pcm.hw_params(&hwp_clone).map_err(AlsaError::Pcm)?;
} else {
pcm.hw_params(&hwp).map_err(AlsaError::Pcm)?;
Expand All @@ -376,7 +381,11 @@ fn open_device(dev_name: &str, format: AudioFormat) -> SinkResult<(PCM, usize)>

let swp = pcm.sw_params_current().map_err(AlsaError::Pcm)?;

swp.set_start_threshold(frames_per_buffer - frames_per_period)
// Cap start_threshold so that playback begins promptly even if the
// device ended up with a large buffer (e.g. after the fallback path).
// One second of latency is a reasonable upper bound.
let start_threshold = (frames_per_buffer - frames_per_period).min(SAMPLE_RATE as Frames);
swp.set_start_threshold(start_threshold)
.map_err(AlsaError::SwParams)?;

pcm.sw_params(&swp).map_err(AlsaError::Pcm)?;
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