Repeater

src/allocator.rs

@@ -1,26 +1,43 @@
-use std::sync::Arc;
-use crate::AudioChunk;
+use crate::*;
 
 pub struct Allocator {
-    buffer_size: usize,
-    allocated_buffer_sender: tokio::sync::mpsc::Sender<Arc<AudioChunk>>,
+    channel: tokio::sync::mpsc::Receiver<Arc<AudioChunk>>,
 }
 
 impl Allocator {
-    pub fn new(buffer_size: usize, allocated_buffer_sender: tokio::sync::mpsc::Sender<Arc<AudioChunk>>) -> Self {
-        while allocated_buffer_sender.try_send(AudioChunk::allocate(buffer_size)).is_ok() {}
-        Self {
-            buffer_size,
-            allocated_buffer_sender,
-        }
-    }
-    
-    pub async fn run(self) {
-        loop {
-            let chunk = AudioChunk::allocate(self.buffer_size);
-            if self.allocated_buffer_sender.send(chunk).await.is_err() {
-                break;
+    pub fn spawn(buffer_size: usize, pool_size: usize) -> (Self, tokio::task::JoinHandle<()>) {
+        let (allocated_buffer_sender, allocated_buffer_receiver) =
+            tokio::sync::mpsc::channel(pool_size);
+
+        // Pre-fill the channel with initial buffers
+        while allocated_buffer_sender
+            .try_send(AudioChunk::allocate(buffer_size))
+            .is_ok()
+        {}
+
+        let allocator = Allocator {
+            channel: allocated_buffer_receiver,
+        };
+
+        // Spawn the background task that continuously allocates buffers
+        let join_handle = tokio::runtime::Handle::current().spawn(async move {
+            loop {
+                let chunk = AudioChunk::allocate(buffer_size);
+                if allocated_buffer_sender.send(chunk).await.is_err() {
+                    break;
+                }
             }
+        });
+
+        (allocator, join_handle)
+    }
+}
+
+impl ChunkFactory for Allocator {
+    fn create_chunk(&mut self) -> Result<std::sync::Arc<AudioChunk>> {
+        match self.channel.try_recv() {
+            Ok(chunk) => Ok(chunk),
+            Err(_) => Err(LooperError::ChunkAllocation(std::panic::Location::caller())),
         }
     }
-}
+}

src/audio_chunk.rs

@@ -8,10 +8,10 @@ use crate::*;
 pub struct AudioChunk {
     /// Fixed-size audio buffer
     pub samples: Box<[f32]>,
-    
+
     /// Number of valid samples (≤ samples.len())
     pub sample_count: usize,
-    
+
     /// Next chunk in linked list
     pub next: Option<Arc<AudioChunk>>,
 }
@@ -25,7 +25,7 @@ impl AudioChunk {
             next: None,
         })
     }
-    
+
     /// Consolidate a linked list of chunks into a single optimized chunk
     pub fn consolidate(this: &Arc<AudioChunk>) -> Arc<Self> {
         // Calculate total sample count
@@ -35,7 +35,7 @@ impl AudioChunk {
             total_samples += chunk.sample_count;
             current = chunk.next.clone();
         }
-        
+
         // Create consolidated buffer
         let mut consolidated_samples = Vec::with_capacity(total_samples);
         let mut current = Some(this.clone());
@@ -43,50 +43,69 @@ impl AudioChunk {
             consolidated_samples.extend_from_slice(&chunk.samples[..chunk.sample_count]);
             current = chunk.next.clone();
         }
-        
+
         Arc::new(Self {
             samples: consolidated_samples.into_boxed_slice(),
             sample_count: total_samples,
             next: None,
         })
     }
-    
-    /// Write samples into this chunk and additional chunks as needed.
+
+    /// Add samples to this chunk and allocate additional chunks as needed.
     /// Uses the factory to get pre-allocated chunks when current chunk fills up.
-    pub fn write_samples<F>(this: &mut Arc<Self>, samples: &[f32], mut chunk_factory: F) -> Result<(), LooperError>
-    where 
-        F: FnMut() -> Result<Arc<AudioChunk>, LooperError>
-    {
-        let sample_count = samples.len();
-        
-        if sample_count > 0 {
-            let available_space = this.samples.len();
-            let samples_to_write = sample_count.min(available_space);
-            
-            // Get mutable access to write samples
-            let chunk_mut = Arc::get_mut(this).ok_or(LooperError::ChunkOwnership)?;
-            
-            // Write what fits
-            if let Some(dest) = chunk_mut.samples.get_mut(..samples_to_write) {
-                dest.copy_from_slice(&samples[..samples_to_write]);
-                chunk_mut.sample_count = samples_to_write;
-            }
-            
-            // Handle remaining samples if any
-            if samples_to_write < sample_count {
-                // Need a new chunk for remaining samples
-                let mut new_chunk = chunk_factory()?;
-                let remaining_samples = &samples[samples_to_write..];
-                
-                // Recurse on the new chunk
-                Self::write_samples(&mut new_chunk, remaining_samples, chunk_factory)?;
-                
+    pub fn append_samples<F: ChunkFactory>(
+        self: &mut Arc<Self>,
+        samples: &[f32],
+        chunk_factory: &mut F,
+    ) -> Result<()> {
+        let mut_self = Arc::get_mut(self)
+            .ok_or(LooperError::ChunkOwnership(std::panic::Location::caller()))?;
+        if let Some(next) = &mut mut_self.next {
+            // Not the last chunk, recurse
+            next.append_samples(samples, chunk_factory)
+        } else {
+            // Add to this chunk first
+            let available_space = mut_self.samples.len() - mut_self.sample_count;
+            let samples_to_append_to_this_chunk = samples.len().min(available_space);
+            let dest = &mut mut_self.samples
+                [mut_self.sample_count..mut_self.sample_count + samples_to_append_to_this_chunk];
+            dest.copy_from_slice(&samples[..samples_to_append_to_this_chunk]);
+            mut_self.sample_count += samples_to_append_to_this_chunk;
+            // Handle remaining samples by recursion
+            if samples_to_append_to_this_chunk < samples.len() {
+                let mut new_chunk = chunk_factory.create_chunk()?;
+                let remaining_samples = &samples[samples_to_append_to_this_chunk..];
+                new_chunk.append_samples(remaining_samples, chunk_factory)?;
                 // Link the new chunk
-                chunk_mut.next = Some(new_chunk);
+                mut_self.next = Some(new_chunk);
+                Ok(())
+            } else {
+                Ok(())
             }
         }
-        
-        Ok(())
+    }
+
+    pub fn copy_samples(self: &Arc<Self>, dest: &mut [f32], start: usize) -> Result<()> {
+        if start < self.sample_count {
+            // Copy from this chunk
+            let end = start + dest.len();
+            if end <= self.sample_count {
+                dest.copy_from_slice(&self.samples[start..end]);
+            } else if let Some(next) = self.next.as_ref() {
+                let sample_count_from_this_chunk = self.sample_count - start;
+                dest[..sample_count_from_this_chunk]
+                    .copy_from_slice(&self.samples[start..self.sample_count]);
+                next.copy_samples(&mut dest[sample_count_from_this_chunk..], 0)?;
+            } else {
+                return Err(LooperError::OutOfBounds(std::panic::Location::caller()));
+            }
+            Ok(())
+        } else if let Some(next) = &self.next {
+            // Copy from next chunk
+            next.copy_samples(dest, start - self.sample_count)
+        } else {
+            Err(LooperError::OutOfBounds(std::panic::Location::caller()))
+        }
     }
 }
 
@@ -97,34 +116,34 @@ mod tests {
     #[test]
     fn test_allocate_creates_empty_chunk() {
         let chunk = AudioChunk::allocate(1024);
-        
+
         assert_eq!(chunk.samples.len(), 1024);
         assert_eq!(chunk.sample_count, 0);
         assert!(chunk.next.is_none());
-        
+
         // All samples should be initialized to 0.0
         assert!(chunk.samples.iter().all(|&x| x == 0.0));
     }
-    
+
     #[test]
     fn test_consolidate_single_chunk() {
         let mut chunk = AudioChunk::allocate(10);
-        
+
         // Write some sample data
         let samples = vec![1.0, 2.0, 3.0, 4.0, 5.0];
-        let factory = || panic!("Factory should not be called");
-        let result = AudioChunk::write_samples(&mut chunk, &samples, factory);
+        let mut factory = || panic!("Factory should not be called");
+        let result = AudioChunk::append_samples(&mut chunk, &samples, &mut factory);
         assert!(result.is_ok());
-        
+
         let consolidated = AudioChunk::consolidate(&chunk);
-        
+
         assert_eq!(consolidated.samples.len(), 5);
         assert_eq!(consolidated.sample_count, 5);
         assert!(consolidated.next.is_none());
         assert_eq!(consolidated.samples[0], 1.0);
         assert_eq!(consolidated.samples[4], 5.0);
     }
-    
+
     #[test]
     fn test_consolidate_linked_chunks() {
         // Create first chunk
@@ -133,21 +152,21 @@ mod tests {
             sample_count: 3,
             next: None,
         });
-        
+
         // Create second chunk
         let chunk2 = Arc::new(AudioChunk {
             samples: vec![4.0, 5.0].into_boxed_slice(),
             sample_count: 2,
             next: None,
         });
-        
+
         // Create third chunk
         let chunk3 = Arc::new(AudioChunk {
             samples: vec![6.0, 7.0, 8.0, 9.0].into_boxed_slice(),
             sample_count: 4,
             next: None,
         });
-        
+
         // Link them together
         let chunk1 = Arc::new(AudioChunk {
             samples: chunk1.samples.clone(),
@@ -158,17 +177,17 @@ mod tests {
                 next: Some(chunk3),
             })),
         });
-        
+
         let consolidated = AudioChunk::consolidate(&chunk1);
-        
+
         assert_eq!(consolidated.samples.len(), 9);
         assert_eq!(consolidated.sample_count, 9);
         assert!(consolidated.next.is_none());
-        
+
         let expected = vec![1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0];
         assert_eq!(consolidated.samples.as_ref(), expected.as_slice());
     }
-    
+
     #[test]
     fn test_consolidate_partial_chunks() {
         // Test chunks where sample_count < samples.len()
@@ -177,48 +196,48 @@ mod tests {
             sample_count: 3, // Only first 3 samples are valid
             next: None,
         });
-        
+
         let chunk2 = Arc::new(AudioChunk {
             samples: vec![4.0, 5.0, 0.0].into_boxed_slice(),
             sample_count: 2, // Only first 2 samples are valid
             next: None,
         });
-        
+
         let chunk1 = Arc::new(AudioChunk {
             samples: chunk1.samples.clone(),
             sample_count: chunk1.sample_count,
             next: Some(chunk2),
         });
-        
+
         let consolidated = AudioChunk::consolidate(&chunk1);
-        
+
         assert_eq!(consolidated.samples.len(), 5);
         assert_eq!(consolidated.sample_count, 5);
-        
+
         let expected = vec![1.0, 2.0, 3.0, 4.0, 5.0];
         assert_eq!(consolidated.samples.as_ref(), expected.as_slice());
     }
-    
+
     #[test]
-    fn test_write_samples_empty() {
+    fn test_append_samples_empty() {
         let mut chunk = AudioChunk::allocate(5);
-        
-        let factory = || panic!("Factory should not be called for empty samples");
-        let result = AudioChunk::write_samples(&mut chunk, &[], factory);
-        
+
+        let mut factory = || panic!("Factory should not be called for empty samples");
+        let result = AudioChunk::append_samples(&mut chunk, &[], &mut factory);
+
         assert!(result.is_ok());
         assert_eq!(chunk.sample_count, 0);
         assert!(chunk.next.is_none());
     }
-    
+
     #[test]
-    fn test_write_samples_fits_in_one_chunk() {
+    fn test_append_samples_fits_in_one_chunk() {
         let mut chunk = AudioChunk::allocate(5);
-        
-        let factory = || panic!("Factory should not be called when samples fit");
+
+        let mut factory = || panic!("Factory should not be called when samples fit");
         let samples = vec![1.0, 2.0, 3.0];
-        let result = AudioChunk::write_samples(&mut chunk, &samples, factory);
-        
+        let result = AudioChunk::append_samples(&mut chunk, &samples, &mut factory);
+
         assert!(result.is_ok());
         assert_eq!(chunk.sample_count, 3);
         assert_eq!(chunk.samples[0], 1.0);
@@ -226,15 +245,15 @@ mod tests {
         assert_eq!(chunk.samples[2], 3.0);
         assert!(chunk.next.is_none());
     }
-    
+
     #[test]
-    fn test_write_samples_exactly_fills_chunk() {
+    fn test_append_samples_exactly_fills_chunk() {
         let mut chunk = AudioChunk::allocate(3);
-        
-        let factory = || panic!("Factory should not be called when samples exactly fit");
+
+        let mut factory = || panic!("Factory should not be called when samples exactly fit");
         let samples = vec![1.0, 2.0, 3.0];
-        let result = AudioChunk::write_samples(&mut chunk, &samples, factory);
-        
+        let result = AudioChunk::append_samples(&mut chunk, &samples, &mut factory);
+
         assert!(result.is_ok());
         assert_eq!(chunk.sample_count, 3);
         assert_eq!(chunk.samples[0], 1.0);
@@ -242,25 +261,23 @@ mod tests {
         assert_eq!(chunk.samples[2], 3.0);
         assert!(chunk.next.is_none());
     }
-    
+
     #[test]
-    fn test_write_samples_requires_new_chunk() {
+    fn test_append_samples_requires_new_chunk() {
         let mut chunk = AudioChunk::allocate(2);
-        
-        use std::cell::RefCell;
-        let available_chunks = RefCell::new(vec![AudioChunk::allocate(3)]);
-        let factory = || available_chunks.borrow_mut().pop().ok_or(LooperError::ChunkAllocation);
-        
+
+        let mut factory = chunk_factory::mock::MockFactory::new(vec![AudioChunk::allocate(3)]);
+
         let samples = vec![1.0, 2.0, 3.0, 4.0]; // 4 samples, first chunk holds 2
-        let result = AudioChunk::write_samples(&mut chunk, &samples, factory);
-        
+        let result = AudioChunk::append_samples(&mut chunk, &samples, &mut factory);
+
         assert!(result.is_ok());
-        
+
         // First chunk: 2 samples
         assert_eq!(chunk.sample_count, 2);
         assert_eq!(chunk.samples[0], 1.0);
         assert_eq!(chunk.samples[1], 2.0);
-        
+
         // Second chunk: remaining 2 samples
         let chunk2 = chunk.next.as_ref().unwrap();
         assert_eq!(chunk2.sample_count, 2);
@@ -268,34 +285,32 @@ mod tests {
         assert_eq!(chunk2.samples[1], 4.0);
         assert!(chunk2.next.is_none());
     }
-    
+
     #[test]
-    fn test_write_samples_multiple_chunks_cascade() {
+    fn test_append_samples_multiple_chunks_cascade() {
         let mut chunk = AudioChunk::allocate(2);
-        
-        use std::cell::RefCell;
-        let available_chunks = RefCell::new(vec![
+
+        let mut factory = chunk_factory::mock::MockFactory::new(vec![
             AudioChunk::allocate(2),
             AudioChunk::allocate(2),
         ]);
-        let factory = || available_chunks.borrow_mut().pop().ok_or(LooperError::ChunkAllocation);
-        
+
         let samples = vec![1.0, 2.0, 3.0, 4.0, 5.0, 6.0]; // 6 samples, each chunk holds 2
-        let result = AudioChunk::write_samples(&mut chunk, &samples, factory);
-        
+        let result = AudioChunk::append_samples(&mut chunk, &samples, &mut factory);
+
         assert!(result.is_ok());
-        
+
         // First chunk
         assert_eq!(chunk.sample_count, 2);
         assert_eq!(chunk.samples[0], 1.0);
         assert_eq!(chunk.samples[1], 2.0);
-        
+
         // Second chunk
         let chunk2 = chunk.next.as_ref().unwrap();
         assert_eq!(chunk2.sample_count, 2);
         assert_eq!(chunk2.samples[0], 3.0);
         assert_eq!(chunk2.samples[1], 4.0);
-        
+
         // Third chunk
         let chunk3 = chunk2.next.as_ref().unwrap();
         assert_eq!(chunk3.sample_count, 2);
@@ -303,42 +318,48 @@ mod tests {
         assert_eq!(chunk3.samples[1], 6.0);
         assert!(chunk3.next.is_none());
     }
-    
+
     #[test]
-    fn test_write_samples_factory_failure() {
+    fn test_append_samples_factory_failure() {
         let mut chunk = AudioChunk::allocate(2);
-        
-        let factory = || Err(LooperError::ChunkAllocation);
+
+        let mut factory = || Err(LooperError::ChunkAllocation(std::panic::Location::caller()));
         let samples = vec![1.0, 2.0, 3.0]; // 3 samples, chunk only holds 2
-        let result = AudioChunk::write_samples(&mut chunk, &samples, factory);
-        
+        let result = AudioChunk::append_samples(&mut chunk, &samples, &mut factory);
+
         assert!(result.is_err());
-        assert!(matches!(result.unwrap_err(), LooperError::ChunkAllocation));
-        
+        assert!(matches!(
+            result.unwrap_err(),
+            LooperError::ChunkAllocation(_)
+        ));
+
         // First chunk should have been written before factory failure
         assert_eq!(chunk.sample_count, 2);
         assert_eq!(chunk.samples[0], 1.0);
         assert_eq!(chunk.samples[1], 2.0);
         assert!(chunk.next.is_none());
     }
-    
+
     #[test]
-    fn test_write_samples_ownership_failure() {
+    fn test_append_samples_ownership_failure() {
         let chunk = AudioChunk::allocate(3);
         let chunk_clone = chunk.clone(); // Create another reference
         let mut chunk_original = chunk;
-        
-        let factory = || panic!("Factory should not be called");
+
+        let mut factory = || panic!("Factory should not be called");
         let samples = vec![1.0, 2.0];
-        let result = AudioChunk::write_samples(&mut chunk_original, &samples, factory);
-        
+        let result = AudioChunk::append_samples(&mut chunk_original, &samples, &mut factory);
+
         assert!(result.is_err());
-        assert!(matches!(result.unwrap_err(), LooperError::ChunkOwnership));
-        
+        assert!(matches!(
+            result.unwrap_err(),
+            LooperError::ChunkOwnership(_)
+        ));
+
         // Chunk should be unchanged
         assert_eq!(chunk_original.sample_count, 0);
-        
+
         // Clean up the clone reference to avoid unused variable warning
         drop(chunk_clone);
     }
-}
+}

src/chunk_factory.rs

@@ -0,0 +1,40 @@
+use crate::*;
+
+/// Creates a new chunk of audio data.
+pub trait ChunkFactory: Send {
+    fn create_chunk(&mut self) -> Result<std::sync::Arc<AudioChunk>>;
+}
+
+impl<F> ChunkFactory for F
+where
+    F: FnMut() -> Result<std::sync::Arc<AudioChunk>> + Send,
+{
+    fn create_chunk(&mut self) -> Result<std::sync::Arc<AudioChunk>> {
+        self()
+    }
+}
+
+#[cfg(test)]
+pub mod mock {
+    use super::*;
+
+    pub struct MockFactory {
+        chunks: Vec<std::sync::Arc<AudioChunk>>,
+    }
+
+    impl MockFactory {
+        pub fn new(chunks: Vec<std::sync::Arc<AudioChunk>>) -> Self {
+            Self { chunks }
+        }
+    }
+
+    impl ChunkFactory for MockFactory {
+        fn create_chunk(&mut self) -> Result<std::sync::Arc<AudioChunk>> {
+            if let Some(chunk) = self.chunks.pop() {
+                Ok(chunk)
+            } else {
+                Err(LooperError::ChunkAllocation(std::panic::Location::caller()))
+            }
+        }
+    }
+}

src/looper_error.rs

@@ -1,8 +1,13 @@
 #[derive(Debug, thiserror::Error)]
 pub enum LooperError {
     #[error("Failed to allocate new audio chunk")]
-    ChunkAllocation,
-    
+    ChunkAllocation(&'static std::panic::Location<'static>),
+
     #[error("Cannot modify chunk with multiple references")]
-    ChunkOwnership,
-}
+    ChunkOwnership(&'static std::panic::Location<'static>),
+
+    #[error("Index out of bounds")]
+    OutOfBounds(&'static std::panic::Location<'static>),
+}
+
+pub type Result<T> = std::result::Result<T, LooperError>;

src/main.rs

@@ -1,30 +1,49 @@
-mod audio_chunk;
-mod looper_error;
 mod allocator;
+mod audio_chunk;
+mod chunk_factory;
+mod looper_error;
+mod process_handler;
+mod track;
+
+use std::sync::Arc;
 
-use audio_chunk::AudioChunk;
-use looper_error::LooperError;
 use allocator::Allocator;
+use audio_chunk::AudioChunk;
+use chunk_factory::ChunkFactory;
+use looper_error::LooperError;
+use looper_error::Result;
+use process_handler::ProcessHandler;
+use track::Track;
 
-fn main() {
-    let (allocated_buffer_sender, mut allocated_buffer_receiver) = tokio::sync::mpsc::channel(1);
-    let allocator = Allocator::new(3, allocated_buffer_sender);
-    let mut factory = move || {
-        match allocated_buffer_receiver.try_recv() {
-            Ok(chunk) => Ok(chunk),
-            Err(_) => Err(LooperError::ChunkAllocation),
-        }
-    };
+#[tokio::main]
+async fn main() {
+    let (allocator, factory_handle) = Allocator::spawn(5000, 100);
 
-    let handle = std::thread::spawn(move || {
-        let mut chunk = factory().unwrap();
-        std::thread::sleep(std::time::Duration::from_millis(100));
-        let samples = vec![1.0, 2.0, 3.0, 4.0, 5.0, 6.0]; // 6 samples, each chunk holds 2
-        AudioChunk::write_samples(&mut chunk, &samples, factory).unwrap();
-        AudioChunk::consolidate(&chunk);
-    });
+    let (jack_client, jack_status) =
+        jack::Client::new("looper", jack::ClientOptions::NO_START_SERVER)
+            .expect("Could not create Jack client");
+    if !jack_status.is_empty() {
+        println!("Could not start jack client: {jack_status:?}");
+        return;
+    }
 
-    let tokio_runtime = tokio::runtime::Builder::new_current_thread().build().unwrap();
-    tokio_runtime.block_on(allocator.run());
-    handle.join().unwrap();
-}
+    let audio_in = jack_client
+        .register_port("audio_in", jack::AudioIn::default())
+        .expect("Could not create audio_in port");
+    let audio_out = jack_client
+        .register_port("audio_out", jack::AudioOut::default())
+        .expect("Could not create audio_out port");
+
+    let process_handler = ProcessHandler::new(audio_in, audio_out, allocator)
+        .expect("Could not create process handler");
+
+    let async_client = jack_client
+        .activate_async((), process_handler)
+        .expect("Could not activate Jack");
+
+    factory_handle.await.unwrap();
+
+    async_client
+        .deactivate()
+        .expect("Could not deactivate Jack");
+}

src/process_handler.rs

@@ -0,0 +1,80 @@
+use crate::*;
+
+pub struct ProcessHandler<F: ChunkFactory> {
+    track: Track,
+    playback_position: usize,
+    input_port: jack::Port<jack::AudioIn>,
+    output_port: jack::Port<jack::AudioOut>,
+    chunk_factory: F,
+}
+
+impl<F: ChunkFactory> ProcessHandler<F> {
+    pub fn new(
+        input_port: jack::Port<jack::AudioIn>,
+        output_port: jack::Port<jack::AudioOut>,
+        mut chunk_factory: F,
+    ) -> Result<Self> {
+        Ok(Self {
+            track: Track::new(&mut chunk_factory)?,
+            playback_position: 0,
+            input_port,
+            output_port,
+            chunk_factory,
+        })
+    }
+}
+
+impl<F: ChunkFactory> jack::ProcessHandler for ProcessHandler<F> {
+    fn process(&mut self, client: &jack::Client, ps: &jack::ProcessScope) -> jack::Control {
+        let input_buffer = self.input_port.as_slice(ps);
+        let output_buffer = self.output_port.as_mut_slice(ps);
+
+        let jack_buffer_size = client.buffer_size() as usize;
+        let recording_samples = client.sample_rate() * 5; // 5 seconds
+
+        let mut index = 0;
+
+        while index < jack_buffer_size {
+            if self.track.len() < recording_samples {
+                // recording
+                let sample_count_to_append = jack_buffer_size - index;
+                let sample_count_to_append =
+                    sample_count_to_append.min(recording_samples - self.track.len());
+                let samples_to_append = &input_buffer[index..index + sample_count_to_append];
+                if self
+                    .track
+                    .append_samples(samples_to_append, &mut self.chunk_factory)
+                    .is_err()
+                {
+                    return jack::Control::Quit;
+                };
+                output_buffer[index..(index + sample_count_to_append)].fill(0.0);
+                index += sample_count_to_append;
+            } else {
+                // playback
+                let sample_count_to_play = jack_buffer_size - index;
+                let sample_count_to_play =
+                    sample_count_to_play.min(self.track.len() - self.playback_position);
+                if self
+                    .track
+                    .copy_samples(
+                        &mut output_buffer[index..(index + sample_count_to_play)],
+                        self.playback_position,
+                    )
+                    .is_err()
+                {
+                    return jack::Control::Quit;
+                }
+                index += sample_count_to_play;
+                self.playback_position += sample_count_to_play;
+                if self.playback_position >= self.track.len() {
+                    self.playback_position = 0;
+                    if self.track.clear(&mut self.chunk_factory).is_err() {
+                        return jack::Control::Quit;
+                    }
+                }
+            }
+        }
+        jack::Control::Continue
+    }
+}

src/track.rs

@@ -0,0 +1,39 @@
+use crate::*;
+
+pub struct Track {
+    audio_chunks: Arc<AudioChunk>,
+    length: usize,
+}
+
+impl Track {
+    pub fn new<F: ChunkFactory>(chunk_factory: &mut F) -> Result<Self> {
+        Ok(Self {
+            audio_chunks: chunk_factory.create_chunk()?,
+            length: 0,
+        })
+    }
+
+    pub fn append_samples<F: ChunkFactory>(
+        &mut self,
+        samples: &[f32],
+        chunk_factory: &mut F,
+    ) -> Result<()> {
+        self.audio_chunks.append_samples(samples, chunk_factory)?;
+        self.length += samples.len();
+        Ok(())
+    }
+
+    pub fn len(&self) -> usize {
+        self.length
+    }
+
+    pub fn clear<F: ChunkFactory>(&mut self, chunk_factory: &mut F) -> Result<()> {
+        self.audio_chunks = chunk_factory.create_chunk()?;
+        self.length = 0;
+        Ok(())
+    }
+
+    pub fn copy_samples(&self, dest: &mut [f32], start: usize) -> Result<()> {
+        self.audio_chunks.copy_samples(dest, start)
+    }
+}