Improved metronome for better xrun handling

src/audio_data.rs

@@ -9,13 +9,13 @@ pub enum AudioData {
     /// Unconsolidated linked chunks with sync offset (used during/after recording)
     Unconsolidated {
         chunks: Arc<AudioChunk>,
-        sync_offset: usize,  // samples from column start to recording start
-        length: usize,       // total samples in recording
+        sync_offset: usize, // samples from column start to recording start
+        length: usize,      // total samples in recording
     },
 
     /// Consolidated single buffer, reordered for optimal playback
     Consolidated {
-        buffer: Box<[f32]>,  // single optimized array
+        buffer: Box<[f32]>, // single optimized array
     },
 }
 
@@ -80,23 +80,20 @@ impl AudioData {
                 output_slice.fill(0.0);
                 Ok(())
             }
-            Self::Unconsolidated { chunks, sync_offset, length } => {
-                self.copy_unconsolidated_samples(
-                    chunks, 
-                    *sync_offset, 
-                    *length, 
-                    output_slice, 
-                    logical_position, 
-                    volume
-                )
-            }
+            Self::Unconsolidated {
+                chunks,
+                sync_offset,
+                length,
+            } => self.copy_unconsolidated_samples(
+                chunks,
+                *sync_offset,
+                *length,
+                output_slice,
+                logical_position,
+                volume,
+            ),
             Self::Consolidated { buffer } => {
-                self.copy_consolidated_samples(
-                    buffer, 
-                    output_slice, 
-                    logical_position, 
-                    volume
-                )
+                self.copy_consolidated_samples(buffer, output_slice, logical_position, volume)
             }
         }
     }
@@ -104,9 +101,11 @@ impl AudioData {
     /// Get underlying chunk for post-record processing
     pub fn get_chunk_for_processing(&self) -> Option<(Arc<AudioChunk>, usize)> {
         match self {
-            Self::Unconsolidated { chunks, sync_offset, .. } => {
-                Some((chunks.clone(), *sync_offset))
-            }
+            Self::Unconsolidated {
+                chunks,
+                sync_offset,
+                ..
+            } => Some((chunks.clone(), *sync_offset)),
             _ => None,
         }
     }
@@ -114,7 +113,9 @@ impl AudioData {
     /// Replace with consolidated buffer from post-record processing
     pub fn set_consolidated_buffer(&mut self, buffer: Box<[f32]>) -> Result<()> {
         match self {
-            Self::Unconsolidated { length: old_length, .. } => {
+            Self::Unconsolidated {
+                length: old_length, ..
+            } => {
                 if buffer.len() != *old_length {
                     return Err(LooperError::OutOfBounds(std::panic::Location::caller()));
                 }
@@ -248,7 +249,11 @@ mod tests {
         let audio_data = AudioData::new_unconsolidated(&mut factory, sync_offset).unwrap();
 
         match audio_data {
-            AudioData::Unconsolidated { sync_offset: offset, length, .. } => {
+            AudioData::Unconsolidated {
+                sync_offset: offset,
+                length,
+                ..
+            } => {
                 assert_eq!(offset, 100);
                 assert_eq!(length, 0);
             }
@@ -284,7 +289,9 @@ mod tests {
         let audio_data = AudioData::new_empty();
         let mut output = vec![99.0; 4]; // Fill with non-zero to verify silence
 
-        audio_data.copy_samples_to_output(&mut output, 0, 1.0).unwrap();
+        audio_data
+            .copy_samples_to_output(&mut output, 0, 1.0)
+            .unwrap();
 
         assert_eq!(output, vec![0.0, 0.0, 0.0, 0.0]);
     }
@@ -299,7 +306,9 @@ mod tests {
         audio_data.append_samples(&samples, &mut factory).unwrap();
 
         let mut output = vec![0.0; 4];
-        audio_data.copy_samples_to_output(&mut output, 0, 1.0).unwrap();
+        audio_data
+            .copy_samples_to_output(&mut output, 0, 1.0)
+            .unwrap();
 
         assert_eq!(output, vec![1.0, 2.0, 3.0, 4.0]);
     }
@@ -316,7 +325,9 @@ mod tests {
         audio_data.append_samples(&samples, &mut factory).unwrap();
 
         let mut output = vec![0.0; 4];
-        audio_data.copy_samples_to_output(&mut output, 0, 1.0).unwrap(); // Start at logical beat 1
+        audio_data
+            .copy_samples_to_output(&mut output, 0, 1.0)
+            .unwrap(); // Start at logical beat 1
 
         // Should get: [C, D, A, B] = [30.0, 40.0, 10.0, 20.0]
         assert_eq!(output, vec![30.0, 40.0, 10.0, 20.0]);
@@ -331,7 +342,9 @@ mod tests {
         audio_data.append_samples(&samples, &mut factory).unwrap();
 
         let mut output = vec![0.0; 4];
-        audio_data.copy_samples_to_output(&mut output, 0, 0.5).unwrap(); // 50% volume
+        audio_data
+            .copy_samples_to_output(&mut output, 0, 0.5)
+            .unwrap(); // 50% volume
 
         assert_eq!(output, vec![0.5, 1.0, 1.5, 2.0]);
     }
@@ -345,7 +358,9 @@ mod tests {
         audio_data.append_samples(&samples, &mut factory).unwrap();
 
         let mut output = vec![0.0; 6]; // Request more samples than available
-        audio_data.copy_samples_to_output(&mut output, 0, 1.0).unwrap();
+        audio_data
+            .copy_samples_to_output(&mut output, 0, 1.0)
+            .unwrap();
 
         // Should loop: [1.0, 2.0, 1.0, 2.0, 1.0, 2.0]
         assert_eq!(output, vec![1.0, 2.0, 1.0, 2.0, 1.0, 2.0]);
@@ -363,7 +378,9 @@ mod tests {
         audio_data.append_samples(&samples, &mut factory).unwrap();
 
         let mut output = vec![0.0; 6]; // Request 2 full loops
-        audio_data.copy_samples_to_output(&mut output, 0, 1.0).unwrap();
+        audio_data
+            .copy_samples_to_output(&mut output, 0, 1.0)
+            .unwrap();
 
         // Should get: [B, C, A, B, C, A] = [20.0, 30.0, 10.0, 20.0, 30.0, 10.0]
         assert_eq!(output, vec![20.0, 30.0, 10.0, 20.0, 30.0, 10.0]);
@@ -377,7 +394,9 @@ mod tests {
         let audio_data = AudioData::Consolidated { buffer };
 
         let mut output = vec![0.0; 4];
-        audio_data.copy_samples_to_output(&mut output, 0, 1.0).unwrap();
+        audio_data
+            .copy_samples_to_output(&mut output, 0, 1.0)
+            .unwrap();
 
         assert_eq!(output, vec![1.0, 2.0, 3.0, 4.0]);
     }
@@ -417,7 +436,9 @@ mod tests {
         // Create consolidated buffer with same length
         let consolidated_buffer = vec![10.0, 20.0, 30.0, 40.0].into_boxed_slice();
 
-        audio_data.set_consolidated_buffer(consolidated_buffer).unwrap();
+        audio_data
+            .set_consolidated_buffer(consolidated_buffer)
+            .unwrap();
 
         // Should now be Consolidated variant
         match audio_data {

src/audio_engine.rs

@@ -1,16 +1,17 @@
 mod allocator;
 mod audio_chunk;
 mod audio_data;
+mod beep;
 mod chunk_factory;
 mod connection_manager;
 mod looper_error;
 mod metronome;
 mod midi;
 mod notification_handler;
+mod persistence_manager;
 mod post_record_handler;
 mod process_handler;
 mod state;
-mod persistence_manager;
 mod track;
 
 use std::sync::Arc;
@@ -18,19 +19,19 @@ use std::sync::Arc;
 use allocator::Allocator;
 use audio_chunk::AudioChunk;
 use audio_data::AudioData;
+use beep::generate_beep;
 use chunk_factory::ChunkFactory;
 use connection_manager::ConnectionManager;
 use looper_error::LooperError;
 use looper_error::Result;
 use metronome::Metronome;
-use metronome::generate_beep;
 use notification_handler::JackNotification;
 use notification_handler::NotificationHandler;
-use post_record_handler::PostRecordHandler;
+use persistence_manager::PersistenceManager;
 use post_record_handler::PostRecordController;
+use post_record_handler::PostRecordHandler;
 use process_handler::ProcessHandler;
 use state::State;
-use persistence_manager::PersistenceManager;
 use track::Track;
 use track::TrackState;
 use track::TrackTiming;
@@ -58,14 +59,15 @@ async fn main() {
     let notification_handler = NotificationHandler::new();
     let mut notification_channel = notification_handler.subscribe();
 
-    let (mut persistence_manager, state_watch) = PersistenceManager::new(notification_handler.subscribe());
+    let (mut persistence_manager, state_watch) =
+        PersistenceManager::new(notification_handler.subscribe());
 
     // Load state values for metronome configuration
     let initial_state = state_watch.borrow().clone();
 
     // Create post-record handler and get controller for ProcessHandler
-    let (mut post_record_handler, post_record_controller) = PostRecordHandler::new()
-        .expect("Could not create post-record handler");
+    let (mut post_record_handler, post_record_controller) =
+        PostRecordHandler::new().expect("Could not create post-record handler");
 
     let process_handler = ProcessHandler::new(
         ports,
@@ -73,7 +75,8 @@ async fn main() {
         beep_samples,
         &initial_state,
         post_record_controller,
-    ).expect("Could not create process handler");
+    )
+    .expect("Could not create process handler");
 
     let mut connection_manager = ConnectionManager::new(
         state_watch,

src/beep.rs

@@ -0,0 +1,25 @@
+use crate::*;
+
+/// Generate a 100ms sine wave beep at 1000Hz
+pub fn generate_beep<F: ChunkFactory>(
+    sample_rate: u32,
+    chunk_factory: &mut F,
+) -> Result<Arc<AudioChunk>> {
+    const FREQUENCY_HZ: f32 = 1000.0;
+    const DURATION_MS: f32 = 100.0;
+
+    let sample_count = ((sample_rate as f32) * (DURATION_MS / 1000.0)) as usize;
+    let mut samples = Vec::with_capacity(sample_count);
+
+    for i in 0..sample_count {
+        let t = i as f32 / sample_rate as f32;
+        let sample = (std::f32::consts::TAU * FREQUENCY_HZ * t).sin();
+        samples.push(sample);
+    }
+
+    // Create AudioChunk and fill it with samples
+    let mut chunk = chunk_factory.create_chunk()?;
+    chunk.append_samples(&samples, chunk_factory)?;
+
+    Ok(chunk)
+}

src/metronome.rs

@@ -1,123 +1,368 @@
 use crate::*;
-use std::f32::consts::TAU;
 
 pub struct Metronome {
     // Audio playback
-    beep_samples: Arc<AudioChunk>,
-    click_volume: f32,               // 0.0 to 1.0
+    click_samples: Arc<AudioChunk>,
+    click_volume: f32,
 
     // Timing state
-    samples_per_beat: u32,
-    beat_time: u32,
+    frames_per_beat: u32,
+    frames_since_last_beat: u32, // Where we are in the current beat cycle
+    last_frame_time: Option<u32>, // For xrun detection
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct BufferTiming {
+    /// Beat index within the current buffer (if any)
+    pub beat_in_buffer: Option<u32>,
+
+    /// Number of frames missed due to xrun (0 if no xrun)
+    pub missed_frames: u32,
+
+    /// Beat index within the missed frames (if any)
+    pub beat_in_missed: Option<u32>,
 }
 
 impl Metronome {
-    pub fn new(beep_samples: Arc<AudioChunk>, state: &State) -> Self {
+    pub fn new(click_samples: Arc<AudioChunk>, state: &State) -> Self {
         Self {
-            beep_samples,
+            click_samples,
             click_volume: state.metronome.click_volume,
-            samples_per_beat: state.metronome.samples_per_beat,
-            beat_time: 0,
+            frames_per_beat: state.metronome.frames_per_beat,
+            frames_since_last_beat: 0,
+            last_frame_time: None,
         }
     }
 
-    pub fn samples_per_beat(&self) -> u32 {
-        self.samples_per_beat
+    pub fn frames_per_beat(&self) -> u32 {
+        self.frames_per_beat
     }
 
     /// Process audio for current buffer, writing to output slice
-    /// Returns the sample index where a beat occurred, if any
-    pub fn process(&mut self, ps: &jack::ProcessScope, ports: &mut JackPorts) -> Result<Option<u32>> {
-        if 0 == self.beat_time {
-            self.beat_time = ps.last_frame_time();
+    pub fn process(
+        &mut self,
+        ps: &jack::ProcessScope,
+        ports: &mut JackPorts,
+    ) -> Result<BufferTiming> {
+        let buffer_size = ps.n_frames();
+        let current_frame_time = ps.last_frame_time();
+
+        // Calculate timing for this buffer
+        let timing = self.calculate_timing(current_frame_time, buffer_size)?;
+
+        // Get output buffer for click track
+        let click_output = ports.click_track_out.as_mut_slice(ps);
+
+        self.render_click(buffer_size, current_frame_time, &timing, click_output);
+
+        Ok(timing)
+    }
+
+    fn render_click(
+        &mut self,
+        buffer_size: u32,
+        current_frame_time: u32,
+        timing: &BufferTiming,
+        click_output: &mut [f32],
+    ) {
+        // Calculate current position within the beep (frames since last beat started)
+        let frames_since_beat_start = current_frame_time - self.frames_since_last_beat;
+        let click_length = self.click_samples.sample_count as u32;
+
+        if let Some(beat_offset) = timing.beat_in_buffer {
+            // Write silence up to beat boundary
+            let silence_end = beat_offset.min(buffer_size);
+            click_output[0..silence_end as _].fill(0.0);
+
+            // Write click samples from boundary onward
+            if beat_offset < buffer_size {
+                let remaining_buffer = buffer_size - beat_offset;
+                let samples_to_write = remaining_buffer.min(click_length);
+
+                // Copy click samples in bulk
+                let dest = &mut click_output
+                    [beat_offset as usize..beat_offset as usize + samples_to_write as usize];
+                if self.click_samples.copy_samples(dest, 0).is_ok() {
+                    // Apply volume scaling with iterators
+                    dest.iter_mut()
+                        .for_each(|sample| *sample *= self.click_volume);
+                }
+
+                // Fill remaining buffer with silence
+                click_output[(beat_offset as usize + samples_to_write as usize)..].fill(0.0);
+            }
+        } else if frames_since_beat_start < click_length {
+            // Continue playing click from previous beat if still within beep duration
+            let click_start_offset = frames_since_beat_start;
+            let remaining_click_samples = click_length - click_start_offset;
+            let samples_to_write = buffer_size.min(remaining_click_samples);
+
+            // Copy remaining beep samples in bulk
+            let dest = &mut click_output[0..samples_to_write as _];
+            if self
+                .click_samples
+                .copy_samples(dest, click_start_offset as _)
+                .is_ok()
+            {
+                // Apply volume scaling with iterators
+                dest.iter_mut()
+                    .for_each(|sample| *sample *= self.click_volume);
+            }
+
+            // Fill remaining buffer with silence
+            click_output[samples_to_write as _..].fill(0.0);
+        } else {
+            click_output.fill(0.0);
         }
+    }
 
-        let time_since_last_beat = ps.last_frame_time() - self.beat_time;
+    pub fn calculate_timing(
+        &mut self,
+        current_frame_time: u32,
+        buffer_size: u32,
+    ) -> Result<BufferTiming> {
+        // Detect xrun
+        let (missed_samples, beat_in_missed) = if let Some(last) = self.last_frame_time {
+            let expected = last.wrapping_add(buffer_size); // Handle u32 wrap
+            if current_frame_time != expected {
+                // We have a gap
+                let missed = current_frame_time.wrapping_sub(expected);
 
-        if time_since_last_beat >= (2 * self.samples_per_beat) && self.beat_time != 0 {
-            return Err(LooperError::Xrun(std::panic::Location::caller()));
-        }
+                // Check if we missed multiple beats
+                let total_samples = self.frames_since_last_beat + missed + buffer_size;
+                if total_samples >= 2 * self.frames_per_beat {
+                    return Err(LooperError::Xrun(std::panic::Location::caller()));
+                }
 
-        let beat_sample_index = if time_since_last_beat >= self.samples_per_beat {
-            self.beat_time += self.samples_per_beat;
-            Some(self.beat_time - ps.last_frame_time())
+                // Check if a beat occurred in the missed section
+                let beat_in_missed = if self.frames_since_last_beat + missed >= self.frames_per_beat
+                {
+                    Some(self.frames_per_beat - self.frames_since_last_beat)
+                } else {
+                    None
+                };
+
+                (missed, beat_in_missed)
+            } else {
+                (0, None)
+            }
+        } else {
+            // First call
+            (0, None)
+        };
+
+        // Check for beat in current buffer
+        // We need to account for any missed samples here too
+        let start_position = (self.frames_since_last_beat + missed_samples) % self.frames_per_beat;
+        let beat_in_buffer = if start_position + buffer_size >= self.frames_per_beat {
+            Some(self.frames_per_beat - start_position)
         } else {
             None
         };
 
-        // Get output buffer for click track
-        let click_output = ports.click_track_out.as_mut_slice(ps);
-        let buffer_size = click_output.len();
+        // Update state - advance by total samples (missed + buffer)
+        self.frames_since_last_beat =
+            (self.frames_since_last_beat + missed_samples + buffer_size) % self.frames_per_beat;
+        self.last_frame_time = Some(current_frame_time);
 
-        // Calculate current position within the beep (frames since last beat started)
-        let frames_since_beat_start = ps.last_frame_time() - self.beat_time;
-        let beep_length = self.beep_samples.sample_count as u32;
+        Ok(BufferTiming {
+            beat_in_buffer,
+            missed_frames: missed_samples,
+            beat_in_missed,
+        })
+    }
+}
 
-        if let Some(beat_offset) = beat_sample_index {
-            let beat_offset = beat_offset as usize;
+#[cfg(test)]
+mod tests {
+    use super::*;
 
-            // Write silence up to beat boundary
-            let silence_end = beat_offset.min(buffer_size);
-            click_output[0..silence_end].fill(0.0);
+    fn create_test_metronome(samples_per_beat: u32) -> Metronome {
+        let beep_samples = Arc::new(AudioChunk {
+            samples: vec![1.0; 100].into_boxed_slice(),
+            sample_count: 100,
+            next: None,
+        });
 
-            // Write beep samples from boundary onward
-            if beat_offset < buffer_size {
-                let remaining_buffer = buffer_size - beat_offset;
-                let samples_to_write = remaining_buffer.min(beep_length as usize);
-                
-                // Copy beep samples in bulk
-                let dest = &mut click_output[beat_offset..beat_offset + samples_to_write];
-                if self.beep_samples.copy_samples(dest, 0).is_ok() {
-                    // Apply volume scaling with iterators
-                    dest.iter_mut().for_each(|sample| *sample *= self.click_volume);
-                }
-                
-                // Fill remaining buffer with silence
-                click_output[(beat_offset + samples_to_write)..].fill(0.0);
-            }
-        } else if frames_since_beat_start < beep_length {
-            // Continue playing beep from previous beat if still within beep duration
-            let beep_start_offset = frames_since_beat_start as usize;
-            let remaining_beep_samples = beep_length as usize - beep_start_offset;
-            let samples_to_write = buffer_size.min(remaining_beep_samples);
-            
-            // Copy remaining beep samples in bulk
-            let dest = &mut click_output[0..samples_to_write];
-            if self.beep_samples.copy_samples(dest, beep_start_offset).is_ok() {
-                // Apply volume scaling with iterators
-                dest.iter_mut().for_each(|sample| *sample *= self.click_volume);
-            }
-            
-            // Fill remaining buffer with silence
-            click_output[samples_to_write..].fill(0.0);
-        } else {
-            click_output.fill(0.0);
+        Metronome {
+            click_samples: beep_samples,
+            click_volume: 1.0,
+            frames_per_beat: samples_per_beat,
+            frames_since_last_beat: 0,
+            last_frame_time: None,
         }
-
-        Ok(beat_sample_index)
-    }
-}
-
-/// Generate a 100ms sine wave beep at 1000Hz
-pub fn generate_beep<F: ChunkFactory>(
-    sample_rate: u32,
-    chunk_factory: &mut F,
-) -> Result<Arc<AudioChunk>> {
-    const FREQUENCY_HZ: f32 = 1000.0;
-    const DURATION_MS: f32 = 100.0;
-    
-    let sample_count = ((sample_rate as f32) * (DURATION_MS / 1000.0)) as usize;
-    let mut samples = Vec::with_capacity(sample_count);
-    
-    for i in 0..sample_count {
-        let t = i as f32 / sample_rate as f32;
-        let sample = (TAU * FREQUENCY_HZ * t).sin();
-        samples.push(sample);
     }
 
-    // Create AudioChunk and fill it with samples
-    let mut chunk = chunk_factory.create_chunk()?;
-    chunk.append_samples(&samples, chunk_factory)?;
+    #[test]
+    fn test_first_call_initialization() {
+        let mut metronome = create_test_metronome(1000);
 
-    Ok(chunk)
+        let result = metronome.calculate_timing(5000, 128).unwrap();
+
+        assert_eq!(metronome.frames_since_last_beat, 128);
+        assert_eq!(metronome.last_frame_time, Some(5000));
+        assert_eq!(result.missed_frames, 0);
+        assert_eq!(result.beat_in_missed, None);
+        assert_eq!(result.beat_in_buffer, None);
+    }
+
+    #[test]
+    fn test_normal_buffer_no_beat() {
+        let mut metronome = create_test_metronome(1000);
+
+        // Initialize at time 1000
+        metronome.calculate_timing(1000, 128).unwrap();
+        assert_eq!(metronome.frames_since_last_beat, 128);
+
+        // Next buffer at 1128 - no beat expected
+        let result = metronome.calculate_timing(1128, 128).unwrap();
+
+        assert_eq!(metronome.frames_since_last_beat, 256);
+        assert_eq!(result.missed_frames, 0);
+        assert_eq!(result.beat_in_missed, None);
+        assert_eq!(result.beat_in_buffer, None);
+    }
+
+    #[test]
+    fn test_beat_in_buffer() {
+        let mut metronome = create_test_metronome(1000);
+
+        // Initialize at time 0
+        metronome.calculate_timing(0, 512).unwrap();
+        assert_eq!(metronome.frames_since_last_beat, 512);
+
+        // Next buffer: 512 -> 1024, beat at 1000 (offset 488)
+        let result = metronome.calculate_timing(512, 512).unwrap();
+
+        assert_eq!(result.missed_frames, 0);
+        assert_eq!(result.beat_in_missed, None);
+        assert_eq!(result.beat_in_buffer, Some(488)); // 1000 - 512
+        assert_eq!(metronome.frames_since_last_beat, 24); // (512 + 512) % 1000
+    }
+
+    #[test]
+    fn test_xrun_no_missed_beat() {
+        let mut metronome = create_test_metronome(1000);
+
+        // Initialize at time 1000
+        metronome.calculate_timing(1000, 128).unwrap();
+        assert_eq!(metronome.frames_since_last_beat, 128);
+
+        // Normal buffer at 1128
+        metronome.calculate_timing(1128, 128).unwrap();
+        assert_eq!(metronome.frames_since_last_beat, 256);
+
+        // Xrun: expected 1256 but got 1428 (172 samples missed)
+        let result = metronome.calculate_timing(1428, 128).unwrap();
+
+        assert_eq!(result.missed_frames, 172);
+        assert_eq!(result.beat_in_missed, None);
+        assert_eq!(result.beat_in_buffer, None);
+        assert_eq!(metronome.frames_since_last_beat, 556); // 256 + 172 + 128
+    }
+
+    #[test]
+    fn test_xrun_with_missed_beat() {
+        let mut metronome = create_test_metronome(1000);
+
+        // Initialize at time 1000
+        metronome.calculate_timing(1000, 128).unwrap();
+        assert_eq!(metronome.frames_since_last_beat, 128);
+
+        // Normal buffer at 1128
+        metronome.calculate_timing(1128, 128).unwrap();
+        assert_eq!(metronome.frames_since_last_beat, 256);
+
+        // Xrun: expected 1256 but got 2228 (972 samples missed)
+        // We're at position 256, miss 972 samples = 1228 total
+        // Beat occurs at position 1000, so beat_in_missed = 1000 - 256 = 744
+        let result = metronome.calculate_timing(2228, 128).unwrap();
+
+        assert_eq!(result.missed_frames, 972);
+        assert_eq!(result.beat_in_missed, Some(744)); // 1000 - 256
+        assert_eq!(result.beat_in_buffer, None);
+        assert_eq!(metronome.frames_since_last_beat, 356); // (256 + 972 + 128) % 1000
+    }
+
+    #[test]
+    fn test_xrun_with_missed_beat_and_upcoming_beat() {
+        let mut metronome = create_test_metronome(1000);
+
+        // Initialize at time 1000
+        metronome.calculate_timing(1000, 128).unwrap();
+
+        // Normal buffer at 1128
+        metronome.calculate_timing(1128, 128).unwrap();
+        assert_eq!(metronome.frames_since_last_beat, 256);
+
+        // Xrun: expected 1256 but got 2078 (822 samples missed)
+        // We're at position 256, miss 822 samples = 1078 total
+        // Beat occurs at position 1000, so beat_in_missed = 1000 - 256 = 744
+        // After missed: position = 78, buffer = 128, no beat in buffer
+        let result = metronome.calculate_timing(2078, 128).unwrap();
+
+        assert_eq!(result.missed_frames, 822);
+        assert_eq!(result.beat_in_missed, Some(744)); // 1000 - 256
+        assert_eq!(result.beat_in_buffer, None); // 78 + 128 < 1000
+        assert_eq!(metronome.frames_since_last_beat, 206); // (256 + 822 + 128) % 1000
+    }
+
+    #[test]
+    fn test_xrun_multiple_beats_error() {
+        let mut metronome = create_test_metronome(1000);
+
+        // Initialize at time 1000
+        metronome.calculate_timing(1000, 128).unwrap();
+
+        // Normal buffer at 1128
+        metronome.calculate_timing(1128, 128).unwrap();
+
+        // Xrun: expected 1256 but got 3328 (2072 samples missed)
+        // Total advancement would be 256 + 2072 + 128 = 2456 samples
+        // That's more than 2 beats (2000 samples), so error
+        let result = metronome.calculate_timing(3328, 128);
+
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn test_consecutive_buffers_with_beat() {
+        let mut metronome = create_test_metronome(1000);
+
+        // First buffer - initialization
+        let result1 = metronome.calculate_timing(0, 512).unwrap();
+        assert_eq!(result1.beat_in_buffer, None);
+        assert_eq!(metronome.frames_since_last_beat, 512);
+
+        // Second buffer - beat should occur at position 1000
+        let result2 = metronome.calculate_timing(512, 512).unwrap();
+        assert_eq!(result2.beat_in_buffer, Some(488)); // 1000 - 512
+        assert_eq!(metronome.frames_since_last_beat, 24); // (512 + 512) % 1000
+
+        // Third buffer - no beat
+        let result3 = metronome.calculate_timing(1024, 512).unwrap();
+        assert_eq!(result3.beat_in_buffer, None);
+        assert_eq!(metronome.frames_since_last_beat, 536);
+
+        // Fourth buffer - next beat at position 1000 again
+        let result4 = metronome.calculate_timing(1536, 512).unwrap();
+        assert_eq!(result4.beat_in_buffer, Some(464)); // 1000 - 536
+        assert_eq!(metronome.frames_since_last_beat, 48); // (536 + 512) % 1000
+    }
+
+    #[test]
+    fn test_u32_wrapping() {
+        let mut metronome = create_test_metronome(1000);
+
+        // Initialize near u32::MAX
+        let start_time = u32::MAX - 100;
+        metronome.calculate_timing(start_time, 128).unwrap();
+
+        // Next buffer wraps around
+        let next_time = start_time.wrapping_add(128);
+        let result = metronome.calculate_timing(next_time, 128).unwrap();
+
+        assert_eq!(result.missed_frames, 0);
+        assert_eq!(metronome.frames_since_last_beat, 256);
+    }
 }

src/notification_handler.rs

@@ -63,7 +63,12 @@ impl jack::NotificationHandler for NotificationHandler {
             .expect("Could not send port connection notification");
     }
 
-    fn port_registration(&mut self, _client: &jack::Client, _port_id: jack::PortId, register: bool) {
+    fn port_registration(
+        &mut self,
+        _client: &jack::Client,
+        _port_id: jack::PortId,
+        register: bool,
+    ) {
         if register {
             let notification = JackNotification::PortRegistered {};
             self.channel

src/post_record_handler.rs

@@ -24,11 +24,20 @@ pub struct PostRecordController {
 
 impl PostRecordController {
     /// Send a post-record processing request (RT-safe)
-    pub fn send_request(&self, chunk_chain: Arc<AudioChunk>, sync_offset: u32, sample_rate: u32) -> Result<()> {
-        let request = PostRecordRequest { chunk_chain, sync_offset, sample_rate };
+    pub fn send_request(
+        &self,
+        chunk_chain: Arc<AudioChunk>,
+        sync_offset: u32,
+        sample_rate: u32,
+    ) -> Result<()> {
+        let request = PostRecordRequest {
+            chunk_chain,
+            sync_offset,
+            sample_rate,
+        };
 
         match self.request_sender.try_send(request) {
-            Ok(true) => Ok(()),  // Successfully sent
+            Ok(true) => Ok(()), // Successfully sent
             Ok(false) => Err(LooperError::ChunkAllocation(std::panic::Location::caller())), // Channel full
             Err(_) => Err(LooperError::ChunkAllocation(std::panic::Location::caller())), // Channel closed
         }
@@ -38,7 +47,7 @@ impl PostRecordController {
     pub fn try_recv_response(&self) -> Option<PostRecordResponse> {
         match self.response_receiver.try_recv() {
             Ok(Some(response)) => Some(response),
-            Ok(None) | Err(_) => None,  // No message or channel closed = None
+            Ok(None) | Err(_) => None, // No message or channel closed = None
         }
     }
 }
@@ -86,23 +95,26 @@ impl PostRecordHandler {
     }
 
     /// Process a single post-record request
-    async fn process_request(
-        &self,
-        request: PostRecordRequest,
-    ) -> Result<()> {
-        log::debug!("Processing post-record request for {} samples with sync_offset {}", 
-                   request.chunk_chain.len(), request.sync_offset);
+    async fn process_request(&self, request: PostRecordRequest) -> Result<()> {
+        log::debug!(
+            "Processing post-record request for {} samples with sync_offset {}",
+            request.chunk_chain.len(),
+            request.sync_offset
+        );
 
         // Step 1: Consolidate and reorder chunk chain based on sync offset
-        let consolidated_buffer = self.consolidate_with_sync_offset(
-            &request.chunk_chain, 
-            request.sync_offset as usize
-        )?;
+        let consolidated_buffer =
+            self.consolidate_with_sync_offset(&request.chunk_chain, request.sync_offset as usize)?;
 
-        log::debug!("Consolidated and reordered {} samples", consolidated_buffer.len());
+        log::debug!(
+            "Consolidated and reordered {} samples",
+            consolidated_buffer.len()
+        );
 
         // Step 2: Send consolidated buffer back to RT thread immediately
-        let response = PostRecordResponse { consolidated_buffer };
+        let response = PostRecordResponse {
+            consolidated_buffer,
+        };
 
         if let Err(_) = self.response_sender.send(response).await {
             log::warn!("Failed to send consolidated buffer to RT thread");
@@ -113,7 +125,10 @@ impl PostRecordHandler {
         let consolidated_chunk = AudioChunk::consolidate(&request.chunk_chain);
         let file_path = self.get_file_path();
 
-        match self.save_wav_file(&consolidated_chunk, request.sample_rate, &file_path).await {
+        match self
+            .save_wav_file(&consolidated_chunk, request.sample_rate, &file_path)
+            .await
+        {
             Ok(_) => log::info!("Saved recording to {:?}", file_path),
             Err(e) => log::error!("Failed to save recording to {:?}: {}", file_path, e),
         }
@@ -122,7 +137,11 @@ impl PostRecordHandler {
     }
 
     /// Consolidate chunk chain and reorder samples based on sync offset
-    fn consolidate_with_sync_offset(&self, chunk_chain: &Arc<AudioChunk>, sync_offset: usize) -> Result<Box<[f32]>> {
+    fn consolidate_with_sync_offset(
+        &self,
+        chunk_chain: &Arc<AudioChunk>,
+        sync_offset: usize,
+    ) -> Result<Box<[f32]>> {
         let total_length = chunk_chain.len();
 
         if total_length == 0 {
@@ -175,11 +194,13 @@ impl PostRecordHandler {
 
             // Write all samples from the chunk
             for sample in chunk_samples {
-                writer.write_sample(sample)
+                writer
+                    .write_sample(sample)
                     .map_err(|_| LooperError::StateSave(std::panic::Location::caller()))?;
             }
 
-            writer.finalize()
+            writer
+                .finalize()
                 .map_err(|_| LooperError::StateSave(std::panic::Location::caller()))?;
 
             Ok::<(), LooperError>(())
@@ -190,8 +211,7 @@ impl PostRecordHandler {
 
     /// Create save directory and return path  
     fn create_directory() -> Result<PathBuf> {
-        let mut path = dirs::home_dir()
-            .unwrap_or_else(|| PathBuf::from("."));
+        let mut path = dirs::home_dir().unwrap_or_else(|| PathBuf::from("."));
         path.push(".fcb_looper");
 
         std::fs::create_dir_all(&path)

src/process_handler.rs

@@ -1,8 +1,8 @@
 use crate::*;
 
 // Testing constants for sync offset functionality
-const SYNC_OFFSET_BEATS: u32 = 2;  // Start recording at beat 3 (0-indexed)
-const AUTO_STOP_BEATS: u32 = 4;    // Record for 4 beats total
+const SYNC_OFFSET_BEATS: u32 = 2; // Start recording at beat 3 (0-indexed)
+const AUTO_STOP_BEATS: u32 = 4; // Record for 4 beats total
 
 pub struct ProcessHandler<F: ChunkFactory> {
     track: Track,
@@ -45,11 +45,12 @@ impl<F: ChunkFactory> ProcessHandler<F> {
 
     /// Handle auto-stop record button (Button 3)
     pub fn record_auto_stop(&mut self) -> Result<()> {
-        let samples_per_beat = self.metronome.samples_per_beat();
+        let samples_per_beat = self.metronome.frames_per_beat();
         let sync_offset = SYNC_OFFSET_BEATS * samples_per_beat;
         let target_samples = AUTO_STOP_BEATS * samples_per_beat;
 
-        self.track.queue_record_auto_stop(target_samples as usize, sync_offset as usize);
+        self.track
+            .queue_record_auto_stop(target_samples as usize, sync_offset as usize);
         Ok(())
     }
 
@@ -75,7 +76,8 @@ impl<F: ChunkFactory> jack::ProcessHandler for ProcessHandler<F> {
                 log::error!("Error processing metronome: {}", e);
                 return jack::Control::Quit;
             }
-        };
+        }
+        .beat_in_buffer;
 
         let buffer_size = client.buffer_size() as usize;
         let state_before = self.track.current_state().clone();
@@ -84,21 +86,22 @@ impl<F: ChunkFactory> jack::ProcessHandler for ProcessHandler<F> {
         let timing = self.calculate_track_timing(beat_sample_index, &state_before);
 
         // Process track audio with calculated timing
-        let should_consolidate = match self.track.process(
-            ps, 
-            &mut self.ports, 
-            timing,
-            &mut self.chunk_factory
-        ) {
-            Ok(consolidate) => consolidate,
-            Err(e) => {
-                log::error!("Error processing track: {}", e);
-                return jack::Control::Quit;
-            }
-        };
+        let should_consolidate =
+            match self
+                .track
+                .process(ps, &mut self.ports, timing, &mut self.chunk_factory)
+            {
+                Ok(consolidate) => consolidate,
+                Err(e) => {
+                    log::error!("Error processing track: {}", e);
+                    return jack::Control::Quit;
+                }
+            };
 
         // Handle post-record processing
-        if let Err(e) = self.handle_post_record_processing(should_consolidate, client.sample_rate() as u32) {
+        if let Err(e) =
+            self.handle_post_record_processing(should_consolidate, client.sample_rate() as u32)
+        {
             log::error!("Error handling post-record processing: {}", e);
             return jack::Control::Quit;
         }
@@ -112,17 +115,26 @@ impl<F: ChunkFactory> jack::ProcessHandler for ProcessHandler<F> {
 
 impl<F: ChunkFactory> ProcessHandler<F> {
     /// Handle post-record processing: send requests and swap buffers
-    fn handle_post_record_processing(&mut self, should_consolidate: bool, sample_rate: u32) -> Result<()> {
+    fn handle_post_record_processing(
+        &mut self,
+        should_consolidate: bool,
+        sample_rate: u32,
+    ) -> Result<()> {
         // Send audio data for processing if track indicates consolidation needed
         if should_consolidate {
             if let Some((chunk_chain, sync_offset)) = self.track.get_audio_data_for_processing() {
-                self.post_record_controller.send_request(chunk_chain, sync_offset as u32, sample_rate)?;
+                self.post_record_controller.send_request(
+                    chunk_chain,
+                    sync_offset as u32,
+                    sample_rate,
+                )?;
             }
         }
 
         // Check for consolidation response
         if let Some(response) = self.post_record_controller.try_recv_response() {
-            self.track.set_consolidated_buffer(response.consolidated_buffer)?;
+            self.track
+                .set_consolidated_buffer(response.consolidated_buffer)?;
         }
 
         Ok(())
@@ -203,7 +215,9 @@ impl<F: ChunkFactory> ProcessHandler<F> {
                 }
 
                 // Check if state transition at beat affects position
-                if state_after == TrackState::Playing && !matches!(state_before, TrackState::Playing) {
+                if state_after == TrackState::Playing
+                    && !matches!(state_before, TrackState::Playing)
+                {
                     // Started playing at beat - reset position to post-beat calculation
                     self.playback_position = self.calculate_post_beat_position(state_before);
                 }

src/state.rs

@@ -16,8 +16,8 @@ pub struct ConnectionState {
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct MetronomeState {
-    pub samples_per_beat: u32,
-    pub click_volume: f32,  // 0.0 to 1.0
+    pub frames_per_beat: u32,
+    pub click_volume: f32, // 0.0 to 1.0
 }
 
 impl Default for State {
@@ -30,12 +30,9 @@ impl Default for State {
                 click_track_out: Vec::new(),
             },
             metronome: MetronomeState {
-                samples_per_beat: 96000, // 120 BPM at 192kHz sample rate
-                click_volume: 0.5,       // Default 50% volume
+                frames_per_beat: 96000, // 120 BPM at 192kHz sample rate
+                click_volume: 0.5,      // Default 50% volume
             },
         }
     }
 }
-
-
-

src/track.rs

@@ -7,21 +7,21 @@ pub enum TrackState {
     Playing,   // Currently playing (PLAY)
     Recording, // Currently recording (REC) - manual stop
     RecordingAutoStop {
-        target_samples: usize,  // Auto-stop when this many samples recorded
-        sync_offset: usize,     // Offset in samples from column start
+        target_samples: usize, // Auto-stop when this many samples recorded
+        sync_offset: usize,    // Offset in samples from column start
     },
 }
 
 #[derive(Debug)]
 pub enum TrackTiming {
     NoBeat {
-        position: usize 
+        position: usize,
     },
     Beat {
         pre_beat_position: usize,
         post_beat_position: usize,
         beat_sample_index: usize,
-    }
+    },
 }
 
 pub struct Track {
@@ -70,7 +70,7 @@ impl Track {
             TrackTiming::Beat {
                 pre_beat_position,
                 post_beat_position,
-                beat_sample_index 
+                beat_sample_index,
             } => {
                 if beat_sample_index > 0 {
                     // Process samples before beat with current state
@@ -129,7 +129,8 @@ impl Track {
             TrackState::Recording => {
                 // Record input samples (manual recording)
                 let samples_to_record = &input_buffer[start_index..end_index];
-                self.audio_data.append_samples(samples_to_record, chunk_factory)?;
+                self.audio_data
+                    .append_samples(samples_to_record, chunk_factory)?;
 
                 // Output silence during recording
                 output_buffer[start_index..end_index].fill(0.0);
@@ -147,7 +148,7 @@ impl Track {
                     if samples_to_append > 0 {
                         self.audio_data.append_samples(
                             &samples_to_record[..samples_to_append],
-                            chunk_factory
+                            chunk_factory,
                         )?;
                     }
 
@@ -175,25 +176,25 @@ impl Track {
 
     /// Apply state transition from next_state to current_state
     /// Returns true if track should be consolidated and saved
-    fn apply_state_transition<F: ChunkFactory>(
-        &mut self, 
-        chunk_factory: &mut F
-    ) -> Result<bool> {
+    fn apply_state_transition<F: ChunkFactory>(&mut self, chunk_factory: &mut F) -> Result<bool> {
         // Check if this is a recording → playing transition (consolidation trigger)
         let should_consolidate = matches!(
             (&self.current_state, &self.next_state),
-            (TrackState::Recording, TrackState::Playing) |
-            (TrackState::RecordingAutoStop { .. }, TrackState::Playing)
+            (TrackState::Recording, TrackState::Playing)
+                | (TrackState::RecordingAutoStop { .. }, TrackState::Playing)
         );
 
         // Handle transitions that require setup
         match (&self.current_state, &self.next_state) {
-            (current_state, TrackState::Recording) if !matches!(current_state, TrackState::Recording) => {
+            (current_state, TrackState::Recording)
+                if !matches!(current_state, TrackState::Recording) =>
+            {
                 // Starting manual recording - clear previous data and create new unconsolidated data
                 self.audio_data = AudioData::new_unconsolidated(chunk_factory, 0)?;
             }
             (current_state, TrackState::RecordingAutoStop { sync_offset, .. })
-                if !matches!(current_state, TrackState::RecordingAutoStop { .. }) => {
+                if !matches!(current_state, TrackState::RecordingAutoStop { .. }) =>
+            {
                 // Starting auto-stop recording - clear previous data and create new unconsolidated data with offset
                 self.audio_data = AudioData::new_unconsolidated(chunk_factory, *sync_offset)?;
             }
@@ -273,19 +274,31 @@ impl Track {
     pub fn queue_record_auto_stop(&mut self, target_samples: usize, sync_offset: usize) {
         match self.current_state {
             TrackState::Empty | TrackState::Idle => {
-                self.next_state = TrackState::RecordingAutoStop { target_samples, sync_offset };
+                self.next_state = TrackState::RecordingAutoStop {
+                    target_samples,
+                    sync_offset,
+                };
             }
             TrackState::Recording => {
                 // Switch from manual to auto-stop recording
-                self.next_state = TrackState::RecordingAutoStop { target_samples, sync_offset };
+                self.next_state = TrackState::RecordingAutoStop {
+                    target_samples,
+                    sync_offset,
+                };
             }
             TrackState::RecordingAutoStop { .. } => {
                 // Already auto-recording - update parameters
-                self.next_state = TrackState::RecordingAutoStop { target_samples, sync_offset };
+                self.next_state = TrackState::RecordingAutoStop {
+                    target_samples,
+                    sync_offset,
+                };
             }
             TrackState::Playing => {
                 // Stop playing and start auto-recording
-                self.next_state = TrackState::RecordingAutoStop { target_samples, sync_offset };
+                self.next_state = TrackState::RecordingAutoStop {
+                    target_samples,
+                    sync_offset,
+                };
             }
         }
     }