fix: use with_buffer_size() after with_supported_config() to prevent underruns

rodio 0.22's with_supported_config() resets buffer_size to Default via
..Default::default(), so our BufferSize settings in StreamConfig were
never reaching CPAL. MixerDeviceSink has zero internal buffering, making
CPAL's buffer the ONLY buffer between the mixer and audio hardware.

Chain .with_buffer_size(Fixed(sample_rate/10)) AFTER with_supported_config()
to actually pass ~100ms buffer to CPAL, matching old vendored cpal behavior.

crates/qbz-audio/src/pipewire_backend.rs

@@ -246,17 +246,12 @@ impl AudioBackend for PipeWireBackend {
         );
 
         // Create StreamConfig with desired sample rate
+        // Note: buffer_size here is unused — with_supported_config() resets it.
+        // The actual buffer size is set via with_buffer_size() below.
         let stream_config = StreamConfig {
             channels: config.channels,
             sample_rate: config.sample_rate,
-            buffer_size: if config.exclusive_mode {
-                BufferSize::Fixed(512)  // Lower latency for exclusive mode
-            } else {
-                // PipeWire manages its own buffer scheduling via quantum;
-                // forcing a fixed buffer size here conflicts and causes underruns
-                // at high sample rates (192kHz)
-                BufferSize::Default
-            },
+            buffer_size: BufferSize::Default,
         };
 
         // Check if device supports this configuration
@@ -296,10 +291,24 @@ impl AudioBackend for PipeWireBackend {
             SampleFormat::F32,
         );
 
+        // Compute buffer size — must be applied AFTER with_supported_config()
+        // because that method resets buffer_size to Default via ..Default::default().
+        // MixerDeviceSink has zero internal buffering, so CPAL's buffer is the
+        // ONLY buffer between the mixer and audio hardware.
+        let cpal_buffer_size = if config.exclusive_mode {
+            BufferSize::Fixed(512)  // Low latency for exclusive mode
+        } else {
+            // ~100ms buffer, matching old vendored cpal period size.
+            // Prevents underruns at high sample rates (192kHz = 19200 frames).
+            BufferSize::Fixed(config.sample_rate / 10)
+        };
+        log::info!("[PipeWire Backend] Buffer size: {:?}", cpal_buffer_size);
+
         // Create MixerDeviceSink with custom config
         let mixer_sink = DeviceSinkBuilder::from_device(device)
             .map_err(|e| format!("Failed to create device sink builder: {}", e))?
             .with_supported_config(&supported_config)
+            .with_buffer_size(cpal_buffer_size)
             .open_stream()
             .map_err(|e| format!("Failed to create output stream at {}Hz: {}", config.sample_rate, e))?;
 

crates/qbz-player/src/player/mod.rs

@@ -352,14 +352,12 @@ fn create_output_stream_with_config(
     );
 
     // Create StreamConfig with desired sample rate
+    // Note: buffer_size here is unused — with_supported_config() resets it.
+    // The actual buffer size is set via with_buffer_size() below.
     let config = StreamConfig {
         channels,
         sample_rate,
-        buffer_size: if exclusive_mode {
-            BufferSize::Fixed(512)  // Lower latency for exclusive mode
-        } else {
-            BufferSize::Default
-        },
+        buffer_size: BufferSize::Default,
     };
 
     // Check if device supports this configuration
@@ -399,10 +397,25 @@ fn create_output_stream_with_config(
         SampleFormat::F32,
     );
 
+    // Compute buffer size — must be applied AFTER with_supported_config()
+    // because that method resets buffer_size to Default via ..Default::default().
+    // MixerDeviceSink has zero internal buffering, so CPAL's buffer is the
+    // ONLY buffer between the mixer and audio hardware.
+    let cpal_buffer_size = if exclusive_mode {
+        BufferSize::Fixed(512)  // Low latency for exclusive mode
+    } else {
+        // ~100ms buffer, matching old vendored cpal period size.
+        // Prevents underruns at high sample rates (192kHz = 19200 frames).
+        BufferSize::Fixed(sample_rate / 10)
+    };
+    log::info!("Buffer size: {:?}", cpal_buffer_size);
+
     // Create MixerDeviceSink with custom config
     match DeviceSinkBuilder::from_device(device) {
         Ok(builder) => {
-            match builder.with_supported_config(&supported_config).open_stream() {
+            match builder.with_supported_config(&supported_config)
+                .with_buffer_size(cpal_buffer_size)
+                .open_stream() {
                 Ok(mixer_sink) => {
                     log::info!("MixerDeviceSink created successfully at {}Hz", sample_rate);
                     Ok(mixer_sink)

src-tauri/src/player/mod.rs

@@ -379,16 +379,12 @@ fn create_output_stream_with_config(
     );
 
     // Create StreamConfig with desired sample rate
+    // Note: buffer_size here is unused — with_supported_config() resets it.
+    // The actual buffer size is set via with_buffer_size() below.
     let config = StreamConfig {
         channels,
         sample_rate,
-        buffer_size: if exclusive_mode {
-            BufferSize::Fixed(512) // Lower latency for exclusive mode
-        } else {
-            // PipeWire manages its own buffer scheduling;
-            // forcing a fixed size causes underruns at high sample rates
-            BufferSize::Default
-        },
+        buffer_size: BufferSize::Default,
     };
 
     // Check if device supports this configuration
@@ -428,10 +424,25 @@ fn create_output_stream_with_config(
         SampleFormat::F32,
     );
 
+    // Compute buffer size — must be applied AFTER with_supported_config()
+    // because that method resets buffer_size to Default via ..Default::default().
+    // MixerDeviceSink has zero internal buffering, so CPAL's buffer is the
+    // ONLY buffer between the mixer and audio hardware.
+    let cpal_buffer_size = if exclusive_mode {
+        BufferSize::Fixed(512)  // Low latency for exclusive mode
+    } else {
+        // ~100ms buffer, matching old vendored cpal period size.
+        // Prevents underruns at high sample rates (192kHz = 19200 frames).
+        BufferSize::Fixed(sample_rate / 10)
+    };
+    log::info!("Buffer size: {:?}", cpal_buffer_size);
+
     // Create MixerDeviceSink with custom config
     match DeviceSinkBuilder::from_device(device) {
         Ok(builder) => {
-            match builder.with_supported_config(&supported_config).open_stream() {
+            match builder.with_supported_config(&supported_config)
+                .with_buffer_size(cpal_buffer_size)
+                .open_stream() {
                 Ok(mixer_sink) => {
                     log::info!("MixerDeviceSink created successfully at {}Hz", sample_rate);
                     Ok(mixer_sink)