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Fix for issue #60, works now with Focusrite 2i4 #70

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Fix for issue #60, works now with Focusrite 2i4 #70

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44 changes: 41 additions & 3 deletions src-tauri/src/audio.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -186,6 +186,24 @@ fn probe_supported_rates(pcm: &alsa::PCM) -> Vec<u32> {
}
}

/// Probe the native channel count of an ALSA device.
/// USB audio interfaces (e.g. Focusrite Scarlett) often expose a fixed
/// channel count that differs from stereo (2ch). Returns the device's
/// minimum supported channels — for USB audio this equals the maximum
/// (the descriptor specifies a single channel count).
#[cfg(target_os = "linux")]
fn probe_native_channels(pcm: &alsa::PCM) -> u32 {
use alsa::pcm::HwParams;

let Ok(hwp) = HwParams::any(pcm) else {
return 2;
};
let ch_min = hwp.get_channels_min().unwrap_or(2);
let ch_max = hwp.get_channels_max().unwrap_or(2);
log::debug!("[audio] DAC channel range: {ch_min}-{ch_max}");
ch_min
}

// ── ALSA writer thread ─────────────────────────────────────────────────

#[cfg(target_os = "linux")]
Expand Down Expand Up @@ -281,8 +299,18 @@ fn configure_alsa_hwparams(
));
}
}
hwp.set_channels(fmt.channels)
.map_err(|e| format!("set_channels({}): {e}", fmt.channels))?;
let hw_channels = if hwp.test_channels(fmt.channels).is_ok() {
fmt.channels
} else {
let native = hwp.get_channels_min().unwrap_or(fmt.channels);
log::info!(
"[audio] DAC doesn't support {}ch, using {}ch",
fmt.channels, native
);
native
};
hwp.set_channels(hw_channels)
.map_err(|e| format!("set_channels({hw_channels}): {e}"))?;
hwp.set_buffer_time_near(500_000, ValueOr::Nearest)
.map_err(|e| format!("set_buffer_time: {e}"))?;
hwp.set_period_time_near(50_000, ValueOr::Nearest)
Expand Down Expand Up @@ -342,7 +370,7 @@ fn configure_alsa_hwparams(
.unwrap_or(fmt.sample_rate);
Ok(PcmFormat {
sample_rate: actual_rate,
channels: fmt.channels,
channels: hw_channels,
gst_format: gst_fmt_str.to_string(),
bytes_per_sample: bps,
})
Expand Down Expand Up @@ -382,6 +410,9 @@ fn spawn_alsa_writer(
let supported_rates = probe_supported_rates(&pcm);
log::debug!("[alsa-writer] DAC supported rates: {:?}", supported_rates);

let native_channels = probe_native_channels(&pcm);
log::debug!("[alsa-writer] DAC native channels: {}", native_channels);

// Adjust initial format to something the DAC actually supports.
// This is a placeholder — the real format arrives via FormatHint/pad_added
// once GStreamer decodes the stream. We just need the DAC to accept it.
Expand All @@ -405,6 +436,13 @@ fn spawn_alsa_writer(
);
fmt.sample_rate = fallback;
}
if fmt.channels != native_channels {
log::info!(
"[alsa-writer] DAC native channels={}, adjusting from {}ch",
native_channels, fmt.channels
);
fmt.channels = native_channels;
}
fmt
};

Expand Down