104 lines
3.0 KiB
Rust
104 lines
3.0 KiB
Rust
/// Diagnostics returned by render downmix helpers.
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#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
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pub(crate) struct RenderDownmixStats {
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/// Peak absolute sample magnitude after i16 conversion.
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pub peak_i16: i16,
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/// Samples clipped while applying output gain.
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pub clipped_samples: u64,
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}
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/// Downmix interleaved stereo f32 samples into mono i16 samples.
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///
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/// The helper is allocation-free and safe for realtime render callbacks.
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/// If the stereo source is shorter than expected, the remainder of `out`
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/// is filled with silence.
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pub(crate) fn downmix_stereo_f32_to_mono_i16(
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stereo: &[f32],
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out: &mut [i16],
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gain: f32,
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muted: bool,
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) -> RenderDownmixStats {
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if muted {
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out.fill(0);
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return RenderDownmixStats::default();
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}
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let available_frames = stereo.len() / 2;
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if available_frames < out.len() {
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out.fill(0);
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}
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let mut peak = 0_u16;
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let mut clipped_samples = 0_u64;
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for (dst, lr) in out.iter_mut().zip(stereo.chunks_exact(2)) {
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let mono = (lr[0] + lr[1]) * 0.5 * gain;
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let clamped = mono.clamp(-1.0, 1.0);
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if (mono - clamped).abs() > f32::EPSILON {
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clipped_samples = clipped_samples.saturating_add(1);
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}
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let sample = (clamped * i16::MAX as f32) as i16;
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*dst = sample;
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peak = peak.max(sample.unsigned_abs());
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}
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RenderDownmixStats {
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peak_i16: peak.min(i16::MAX as u16) as i16,
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clipped_samples,
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}
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}
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/// Downmix interleaved stereo f32 samples into mono f32 samples.
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///
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/// Used for software-AEC render references and debug WAV taps.
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#[cfg(any(target_os = "ios", test))]
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pub(crate) fn downmix_stereo_f32_to_mono_f32(stereo: &[f32], out: &mut [f32]) {
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let available_frames = stereo.len() / 2;
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if available_frames < out.len() {
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out.fill(0.0);
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}
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for (dst, lr) in out.iter_mut().zip(stereo.chunks_exact(2)) {
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*dst = (lr[0] + lr[1]) * 0.5;
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn downmix_i16_applies_gain_and_reports_clipping() {
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let stereo = [1.0_f32, 1.0, 0.25, -0.25, -2.0, -2.0];
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let mut out = [0_i16; 3];
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let stats = downmix_stereo_f32_to_mono_i16(&stereo, &mut out, 2.0, false);
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assert_eq!(out[0], i16::MAX);
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assert_eq!(out[1], 0);
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assert_eq!(out[2], -i16::MAX);
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assert_eq!(stats.peak_i16, i16::MAX);
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assert_eq!(stats.clipped_samples, 2);
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}
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#[test]
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fn downmix_i16_mutes_output() {
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let stereo = [1.0_f32, 1.0, -1.0, -1.0];
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let mut out = [123_i16; 2];
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let stats = downmix_stereo_f32_to_mono_i16(&stereo, &mut out, 1.0, true);
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assert_eq!(out, [0, 0]);
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assert_eq!(stats, RenderDownmixStats::default());
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}
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#[test]
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fn downmix_f32_fills_missing_tail_with_silence() {
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let stereo = [1.0_f32, -1.0];
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let mut out = [9.0_f32; 2];
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downmix_stereo_f32_to_mono_f32(&stereo, &mut out);
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assert_eq!(out, [0.0, 0.0]);
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}
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}
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