feat: add hardware latency reporting to ASIO, CoreAudio, JACK, WASAPI, and WebAudio

Author: roderickvd

CHANGELOG.md

@@ -31,7 +31,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **ALSA**: Polling errors trigger underrun recovery instead of looping.
 - **ALSA**: Try to resume from hardware after a system suspend.
 - **ASIO**: `Device::driver`, `asio_streams`, and `current_callback_flag` are no longer `pub`.
+- **ASIO**: Timestamps now include driver-reported hardware latency.
+- **CoreAudio**: Timestamps now include device latency and safety offset.
+- **JACK**: Timestamps now use the precise hardware deadline.
 - **Linux/BSD**: Default host now is, in order from first to last available: PipeWire, PulseAudio, ALSA.
+- **WASAPI**: Timestamps now include hardware pipeline latency.
+- **WebAudio**: Timestamps now include base and output latency.
 
 ### Fixed
 

asio-sys/CHANGELOG.md

@@ -5,6 +5,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Added
+- Added `Driver::latencies()`
+
 ## [0.2.6] - 2026-02-18
 
 ### Fixed
@@ -82,6 +87,7 @@ Initial release.
 - Support for MSVC toolchain on Windows
 - Basic error types: `AsioError`, `LoadDriverError`
 
+[Unreleased]: https://github.com/RustAudio/cpal/compare/asio-sys-v0.2.6...HEAD
 [0.2.6]: https://github.com/RustAudio/cpal/compare/asio-sys-v0.2.5...asio-sys-v0.2.6
 [0.2.5]: https://github.com/RustAudio/cpal/compare/asio-sys-v0.2.4...asio-sys-v0.2.5
 [0.2.4]: https://github.com/RustAudio/cpal/compare/asio-sys-v0.2.3...asio-sys-v0.2.4

asio-sys/asio_stub_bindings.rs

@@ -137,6 +137,13 @@ pub unsafe extern "C" fn ASIOGetChannels(_ins: *mut c_long, _outs: *mut c_long)
     0
 }
 #[no_mangle]
+pub unsafe extern "C" fn ASIOGetLatencies(
+    _in_latency: *mut c_long,
+    _out_latency: *mut c_long,
+) -> ASIOError {
+    0
+}
+#[no_mangle]
 pub unsafe extern "C" fn ASIOGetChannelInfo(_info: *mut ASIOChannelInfo) -> ASIOError {
     0
 }

asio-sys/build.rs

@@ -228,6 +228,7 @@ fn create_bindings(cpal_asio_dir: &PathBuf) {
         .allowlist_function("ASIOGetChannels")
         .allowlist_function("ASIOGetChannelInfo")
         .allowlist_function("ASIOGetBufferSize")
+        .allowlist_function("ASIOGetLatencies")
         .allowlist_function("ASIOGetSamplePosition")
         .allowlist_function("ASIOOutputReady")
         .allowlist_function("get_sample_rate")

asio-sys/src/bindings/mod.rs

@@ -458,6 +458,19 @@ impl Driver {
         Ok(channel)
     }
 
+    /// Get the input and output hardware latency in frames.
+    pub fn latencies(&self) -> Result<(c_long, c_long), AsioError> {
+        let mut input_latency: c_long = 0;
+        let mut output_latency: c_long = 0;
+        unsafe {
+            asio_result!(ai::ASIOGetLatencies(
+                &mut input_latency,
+                &mut output_latency
+            ))?;
+        }
+        Ok((input_latency, output_latency))
+    }
+
     /// Get the min and max supported buffersize of the driver.
     pub fn buffersize_range(&self) -> Result<(c_long, c_long), AsioError> {
         let buffer_sizes = asio_get_buffer_sizes()?;

src/host/asio/stream.rs

@@ -96,6 +96,12 @@ impl Device {
         let playing = Arc::clone(&stream_playing);
         let asio_streams = self.asio_streams.clone();
 
+        // Query hardware input latency (order matters: needs buffers created above).
+        let hardware_input_latency = driver
+            .latencies()
+            .map(|(input, _)| input.max(0) as usize)
+            .unwrap_or(0);
+
         // Set the input callback.
         // This is most performance critical part of the ASIO bindings.
         let callback_id = driver.add_callback(move |callback_info| unsafe {
@@ -113,6 +119,7 @@ impl Device {
 
             /// 1. Write from the ASIO buffer to the interleaved CPAL buffer.
             /// 2. Deliver the CPAL buffer to the user callback.
+            #[allow(clippy::too_many_arguments)]
             unsafe fn process_input_callback<A, D, F>(
                 data_callback: &mut D,
                 interleaved: &mut [u8],
@@ -121,6 +128,7 @@ impl Device {
                 sample_rate: crate::SampleRate,
                 format: SampleFormat,
                 from_endianness: F,
+                hardware_latency_frames: usize,
             ) where
                 A: Copy,
                 D: FnMut(&Data, &InputCallbackInfo) + Send + 'static,
@@ -147,6 +155,7 @@ impl Device {
                     asio_info,
                     sample_rate,
                     format,
+                    hardware_latency_frames,
                 );
             }
 
@@ -160,6 +169,7 @@ impl Device {
                         config.sample_rate,
                         SampleFormat::I16,
                         from_le,
+                        hardware_input_latency,
                     );
                 }
                 (&sys::AsioSampleType::ASIOSTInt16MSB, SampleFormat::I16) => {
@@ -171,6 +181,7 @@ impl Device {
                         config.sample_rate,
                         SampleFormat::I16,
                         from_be,
+                        hardware_input_latency,
                     );
                 }
 
@@ -183,6 +194,7 @@ impl Device {
                         config.sample_rate,
                         SampleFormat::F32,
                         from_le,
+                        hardware_input_latency,
                     );
                 }
                 (&sys::AsioSampleType::ASIOSTFloat32MSB, SampleFormat::F32) => {
@@ -194,6 +206,7 @@ impl Device {
                         config.sample_rate,
                         SampleFormat::F32,
                         from_be,
+                        hardware_input_latency,
                     );
                 }
 
@@ -206,6 +219,7 @@ impl Device {
                         config.sample_rate,
                         SampleFormat::I32,
                         from_le,
+                        hardware_input_latency,
                     );
                 }
                 (&sys::AsioSampleType::ASIOSTInt32MSB, SampleFormat::I32) => {
@@ -217,6 +231,7 @@ impl Device {
                         config.sample_rate,
                         SampleFormat::I32,
                         from_be,
+                        hardware_input_latency,
                     );
                 }
 
@@ -229,6 +244,7 @@ impl Device {
                         config.sample_rate,
                         SampleFormat::F64,
                         from_le,
+                        hardware_input_latency,
                     );
                 }
                 (&sys::AsioSampleType::ASIOSTFloat64MSB, SampleFormat::F64) => {
@@ -240,6 +256,7 @@ impl Device {
                         config.sample_rate,
                         SampleFormat::F64,
                         from_be,
+                        hardware_input_latency,
                     );
                 }
 
@@ -251,6 +268,7 @@ impl Device {
                         callback_info,
                         config.sample_rate,
                         true,
+                        hardware_input_latency,
                     );
                 }
                 (&sys::AsioSampleType::ASIOSTInt24MSB, SampleFormat::I24) => {
@@ -261,6 +279,7 @@ impl Device {
                         callback_info,
                         config.sample_rate,
                         false,
+                        hardware_input_latency,
                     );
                 }
 
@@ -334,6 +353,12 @@ impl Device {
         let playing = Arc::clone(&stream_playing);
         let asio_streams = self.asio_streams.clone();
 
+        // Query hardware input latency (order matters: needs buffers created above).
+        let hardware_output_latency = driver
+            .latencies()
+            .map(|(_, output)| output.max(0) as usize)
+            .unwrap_or(0);
+
         let callback_id = driver.add_callback(move |callback_info| unsafe {
             // If not playing, return early.
             if !playing.load(Ordering::SeqCst) {
@@ -372,6 +397,7 @@ impl Device {
                 sample_rate: crate::SampleRate,
                 format: SampleFormat,
                 mix_samples: F,
+                hardware_latency_frames: usize,
             ) where
                 A: Copy,
                 D: FnMut(&mut Data, &OutputCallbackInfo) + Send + 'static,
@@ -385,6 +411,7 @@ impl Device {
                     asio_info,
                     sample_rate,
                     format,
+                    hardware_latency_frames,
                 );
                 let n_channels = interleaved.len() / asio_stream.buffer_size as usize;
                 let buffer_index = asio_info.buffer_index as usize;
@@ -415,6 +442,7 @@ impl Device {
                         |old_sample, new_sample| {
                             from_le(old_sample).saturating_add(new_sample).to_le()
                         },
+                        hardware_output_latency,
                     );
                 }
                 (SampleFormat::I16, &sys::AsioSampleType::ASIOSTInt16MSB) => {
@@ -429,6 +457,7 @@ impl Device {
                         |old_sample, new_sample| {
                             from_be(old_sample).saturating_add(new_sample).to_be()
                         },
+                        hardware_output_latency,
                     );
                 }
                 (SampleFormat::F32, &sys::AsioSampleType::ASIOSTFloat32LSB) => {
@@ -445,6 +474,7 @@ impl Device {
                                 .to_bits()
                                 .to_le()
                         },
+                        hardware_output_latency,
                     );
                 }
 
@@ -462,6 +492,7 @@ impl Device {
                                 .to_bits()
                                 .to_be()
                         },
+                        hardware_output_latency,
                     );
                 }
 
@@ -477,6 +508,7 @@ impl Device {
                         |old_sample, new_sample| {
                             from_le(old_sample).saturating_add(new_sample).to_le()
                         },
+                        hardware_output_latency,
                     );
                 }
                 (SampleFormat::I32, &sys::AsioSampleType::ASIOSTInt32MSB) => {
@@ -491,6 +523,7 @@ impl Device {
                         |old_sample, new_sample| {
                             from_be(old_sample).saturating_add(new_sample).to_be()
                         },
+                        hardware_output_latency,
                     );
                 }
 
@@ -508,6 +541,7 @@ impl Device {
                                 .to_bits()
                                 .to_le()
                         },
+                        hardware_output_latency,
                     );
                 }
 
@@ -525,6 +559,7 @@ impl Device {
                                 .to_bits()
                                 .to_be()
                         },
+                        hardware_output_latency,
                     );
                 }
 
@@ -537,6 +572,7 @@ impl Device {
                         asio_stream,
                         callback_info,
                         config.sample_rate,
+                        hardware_output_latency,
                     );
                 }
 
@@ -549,6 +585,7 @@ impl Device {
                         asio_stream,
                         callback_info,
                         config.sample_rate,
+                        hardware_output_latency,
                     );
                 }
 
@@ -853,6 +890,7 @@ fn i24_bytes_to_i32(i24_bytes: &[u8; 3], little_endian: bool) -> i32 {
     }
 }
 
+#[allow(clippy::too_many_arguments)]
 unsafe fn process_output_callback_i24<D>(
     data_callback: &mut D,
     interleaved: &mut [u8],
@@ -861,6 +899,7 @@ unsafe fn process_output_callback_i24<D>(
     asio_stream: &mut sys::AsioStream,
     asio_info: &sys::CallbackInfo,
     sample_rate: crate::SampleRate,
+    hardware_latency_frames: usize,
 ) where
     D: FnMut(&mut Data, &OutputCallbackInfo) + Send + 'static,
 {
@@ -873,6 +912,7 @@ unsafe fn process_output_callback_i24<D>(
         asio_info,
         sample_rate,
         format,
+        hardware_latency_frames,
     );
 
     // Size of samples in the ASIO buffer (has to be 3 in this case)
@@ -930,6 +970,7 @@ unsafe fn process_input_callback_i24<D>(
     asio_info: &sys::CallbackInfo,
     sample_rate: crate::SampleRate,
     little_endian: bool,
+    hardware_latency_frames: usize,
 ) where
     D: FnMut(&Data, &InputCallbackInfo) + Send + 'static,
 {
@@ -969,6 +1010,7 @@ unsafe fn process_input_callback_i24<D>(
         asio_info,
         sample_rate,
         format,
+        hardware_latency_frames,
     );
 }
 
@@ -980,6 +1022,7 @@ unsafe fn apply_output_callback_to_data<A, D>(
     asio_info: &sys::CallbackInfo,
     sample_rate: crate::SampleRate,
     sample_format: SampleFormat,
+    hardware_latency_frames: usize,
 ) where
     A: Copy,
     D: FnMut(&mut Data, &OutputCallbackInfo) + Send + 'static,
@@ -990,7 +1033,10 @@ unsafe fn apply_output_callback_to_data<A, D>(
         sample_format,
     );
     let callback = system_time_to_stream_instant(asio_info.system_time);
-    let delay = frames_to_duration(asio_stream.buffer_size as usize, sample_rate);
+    let delay = frames_to_duration(
+        asio_stream.buffer_size as usize + hardware_latency_frames,
+        sample_rate,
+    );
     let playback = callback
         .add(delay)
         .expect("`playback` occurs beyond representation supported by `StreamInstant`");
@@ -1007,6 +1053,7 @@ unsafe fn apply_input_callback_to_data<A, D>(
     asio_info: &sys::CallbackInfo,
     sample_rate: crate::SampleRate,
     format: SampleFormat,
+    hardware_latency_frames: usize,
 ) where
     A: Copy,
     D: FnMut(&Data, &InputCallbackInfo) + Send + 'static,
@@ -1017,7 +1064,10 @@ unsafe fn apply_input_callback_to_data<A, D>(
         format,
     );
     let callback = system_time_to_stream_instant(asio_info.system_time);
-    let delay = frames_to_duration(asio_stream.buffer_size as usize, sample_rate);
+    let delay = frames_to_duration(
+        asio_stream.buffer_size as usize + hardware_latency_frames,
+        sample_rate,
+    );
     let capture = callback
         .sub(delay)
         .expect("`capture` occurs before origin of alsa `StreamInstant`");