Adapt playback speed to chunk audio boundary

Signed-off-by: John Tennant <johnmatthewtennant@gmail.com>

desktop/src-tauri/examples/tts_speed_probe.rs

@@ -13,26 +13,19 @@ fn main() {
             (2.0 * std::f32::consts::PI * 220.0 * index as f32 / SAMPLE_RATE as f32).sin() * 0.25
         })
         .collect();
-    let mut input = Vec::with_capacity(SENTENCE_LEAD_IN_SAMPLES + tone.len());
-    input.resize(SENTENCE_LEAD_IN_SAMPLES, 0.0);
-    input.extend_from_slice(&tone);
 
     let compensated_lookahead = playback_speed_dsp::compensated_output_latency_samples(SAMPLE_RATE);
     let compensated_lookahead_ms = compensated_lookahead as f64 * 1_000.0 / SAMPLE_RATE as f64;
+    let fixed_lead_in_ms = SENTENCE_LEAD_IN_SAMPLES as f64 * 1_000.0 / SAMPLE_RATE as f64;
 
     for speed in [0.75_f32, 1.25, 1.5] {
         let started = Instant::now();
-        let output = playback_speed_dsp::process_complete_chunk_preserving_lead_in(
-            &input,
-            SENTENCE_LEAD_IN_SAMPLES,
-            speed,
-            SAMPLE_RATE,
-        )
-        .expect("process production-shaped buffer");
+        let output = playback_speed_dsp::process_complete_chunk(&tone, speed, SAMPLE_RATE)
+            .expect("process synthesized model audio");
         let elapsed = started.elapsed();
         println!(
             "{speed:.2}x: processing={:.2}ms, {:.3}% realtime, output={} samples, compensated \
-             lookahead={compensated_lookahead_ms:.1}ms",
+             lookahead={compensated_lookahead_ms:.1}ms, fixed playback lead-in={fixed_lead_in_ms:.1}ms",
             elapsed.as_secs_f64() * 1_000.0,
             elapsed.as_secs_f64() / TONE_SECONDS * 100.0,
             output.len(),

desktop/src-tauri/src/huddle/playback_speed.rs

@@ -21,12 +21,12 @@ use crate::app_state::AppState;
 
 #[path = "playback_speed_dsp.rs"]
 mod playback_speed_dsp;
-pub(crate) use playback_speed_dsp::process_complete_chunk_preserving_lead_in;
+pub(crate) use playback_speed_dsp::process_complete_chunk;
 use playback_speed_dsp::{validate_speed, DEFAULT_PLAYBACK_SPEED};
 
 const SETTINGS_FILE: &str = "tts-playback-settings.json";
 #[cfg(test)]
-use playback_speed_dsp::{process_complete_chunk, UNITY_EPSILON};
+use playback_speed_dsp::UNITY_EPSILON;
 
 /// Lock-free shared control read by the TTS worker before each synthesis chunk.
 #[derive(Clone, Debug)]

desktop/src-tauri/src/huddle/playback_speed_dsp.rs

@@ -71,27 +71,6 @@ pub fn process_complete_chunk(
     Ok(output[0][start..end].to_vec())
 }
 
-/// Preserve a fixed device lead-in while pitch-preserving the remaining audio.
-pub(crate) fn process_complete_chunk_preserving_lead_in(
-    input: &[f32],
-    fixed_lead_in_samples: usize,
-    speed: f32,
-    sample_rate: u32,
-) -> Result<Vec<f32>, String> {
-    if fixed_lead_in_samples > input.len() {
-        return Err(format!(
-            "fixed lead-in of {fixed_lead_in_samples} samples exceeds input length {}",
-            input.len()
-        ));
-    }
-
-    let processed = process_complete_chunk(&input[fixed_lead_in_samples..], speed, sample_rate)?;
-    let mut output = Vec::with_capacity(fixed_lead_in_samples + processed.len());
-    output.extend_from_slice(&input[..fixed_lead_in_samples]);
-    output.extend_from_slice(&processed);
-    Ok(output)
-}
-
 /// Return Signalsmith's compensated output lookahead for descriptive reporting.
 #[allow(dead_code)]
 pub(crate) fn compensated_output_latency_samples(sample_rate: u32) -> usize {