feat(macos): add CoreAudio device probing and sample rate switching

Add coreaudio_direct module using coreaudio-rs safe wrappers for:
- Device capability probing (supported sample rates, transport type)
- Automatic sample rate switching per-track
- Device lookup by name for CoreAudio↔CPAL bridging

Uses a fork branch of coreaudio-rs that adds get_available_sample_rates
and get_device_transport_type helpers (PR RustAudio/coreaudio-rs#149).

crates/qbz-audio/Cargo.toml

@@ -39,3 +39,8 @@ dirs = "5"
 [target.'cfg(target_os = "linux")'.dependencies]
 # ALSA for direct hardware access (bit-perfect)
 alsa = "0.9"
+
+[target.'cfg(target_os = "macos")'.dependencies]
+# CoreAudio for device probing, sample rate switching, and (future) hog mode / exclusive mode
+# Using fork branch until https://github.com/RustAudio/coreaudio-rs/pull/149 is merged
+coreaudio-rs = { git = "https://github.com/afonsojramos/coreaudio-rs.git", branch = "feat/device-helpers" }

crates/qbz-audio/src/coreaudio_direct.rs

@@ -0,0 +1,165 @@
+//! CoreAudio direct access for macOS
+//!
+//! Provides device capability probing and sample rate switching on macOS
+//! using the coreaudio-rs safe wrappers.
+//!
+//! Phase 1: Device probing + nominal sample rate switching (shared mode)
+//! Phase 2 (future): Hog mode + integer mode + IO proc for bit-perfect playback
+
+#[cfg(target_os = "macos")]
+use coreaudio::audio_unit::macos_helpers;
+#[cfg(target_os = "macos")]
+use coreaudio::audio_unit::Scope;
+
+/// CoreAudio device ID (re-exported so callers don't need objc2_core_audio)
+#[cfg(target_os = "macos")]
+pub type AudioDeviceID = u32;
+
+// CoreAudio transport type constants (FourCC values from AudioHardware.h)
+#[cfg(target_os = "macos")]
+mod transport_types {
+    pub const BUILT_IN: u32 = 0x626c746e;    // 'bltn'
+    pub const USB: u32 = 0x75736220;          // 'usb '
+    pub const BLUETOOTH: u32 = 0x626c7565;    // 'blue'
+    pub const BLUETOOTH_LE: u32 = 0x626c6561; // 'blea'
+    pub const HDMI: u32 = 0x68646d69;         // 'hdmi'
+    pub const DISPLAY_PORT: u32 = 0x64707274; // 'dprt'
+    pub const THUNDERBOLT: u32 = 0x7468756e;  // 'thun'
+    pub const FIREWIRE: u32 = 0x31333934;     // '1394'
+    pub const VIRTUAL: u32 = 0x76697274;      // 'virt'
+    pub const AGGREGATE: u32 = 0x67727570;    // 'grup'
+}
+
+/// Common audio sample rates to check against device capabilities
+#[cfg(target_os = "macos")]
+const COMMON_SAMPLE_RATES: &[u32] = &[
+    44100, 48000, 88200, 96000, 176400, 192000, 352800, 384000, 705600, 768000,
+];
+
+/// Query supported sample rates for a CoreAudio device.
+/// Returns discrete rates from the device's available nominal sample rate ranges.
+#[cfg(target_os = "macos")]
+pub fn query_supported_sample_rates(device_id: AudioDeviceID) -> Result<Vec<u32>, String> {
+    let ranges = macos_helpers::get_available_sample_rates(device_id)
+        .map_err(|e| format!("Failed to get sample rate ranges: {:?}", e))?;
+
+    let mut rates = Vec::new();
+    for range in &ranges {
+        if (range.mMinimum - range.mMaximum).abs() < 0.5 {
+            // Point value (min == max)
+            rates.push(range.mMinimum as u32);
+        } else {
+            // Continuous range — check which common rates fall within it
+            for &rate in COMMON_SAMPLE_RATES {
+                let rate_f = rate as f64;
+                if rate_f >= range.mMinimum && rate_f <= range.mMaximum {
+                    rates.push(rate);
+                }
+            }
+        }
+    }
+
+    rates.sort_unstable();
+    rates.dedup();
+    Ok(rates)
+}
+
+/// Set the nominal sample rate of a device.
+/// Delegates to coreaudio-rs which handles async confirmation with a 2-second timeout.
+#[cfg(target_os = "macos")]
+pub fn set_nominal_sample_rate(device_id: AudioDeviceID, target_rate: u32) -> Result<(), String> {
+    log::info!(
+        "[CoreAudio] Switching sample rate to {}Hz on device {}",
+        target_rate,
+        device_id
+    );
+
+    macos_helpers::set_device_sample_rate(device_id, target_rate as f64)
+        .map_err(|e| format!("Failed to set sample rate to {}Hz: {:?}", target_rate, e))?;
+
+    log::info!("[CoreAudio] Sample rate switched to {}Hz", target_rate);
+    Ok(())
+}
+
+/// Get the default output device ID.
+#[cfg(target_os = "macos")]
+pub fn get_default_output_device() -> Result<AudioDeviceID, String> {
+    macos_helpers::get_default_device_id(false)
+        .ok_or_else(|| "No default output device found".to_string())
+}
+
+/// Get all output device IDs.
+#[cfg(target_os = "macos")]
+pub fn get_output_device_ids() -> Result<Vec<AudioDeviceID>, String> {
+    macos_helpers::get_audio_device_ids_for_scope(Scope::Output)
+        .map_err(|e| format!("Failed to enumerate output devices: {:?}", e))
+}
+
+/// Get the name of a CoreAudio device.
+#[cfg(target_os = "macos")]
+pub fn get_device_name(device_id: AudioDeviceID) -> Result<String, String> {
+    macos_helpers::get_device_name(device_id)
+        .map_err(|e| format!("Failed to get device name: {:?}", e))
+}
+
+/// Find a CoreAudio output device ID by its name.
+#[cfg(target_os = "macos")]
+pub fn find_device_by_name(name: &str) -> Result<Option<AudioDeviceID>, String> {
+    // get_device_id_from_name: input=false means output device
+    Ok(macos_helpers::get_device_id_from_name(name, false))
+}
+
+/// Get the transport type of a device (USB, built-in, Bluetooth, etc.)
+#[cfg(target_os = "macos")]
+pub fn get_device_transport_type(device_id: AudioDeviceID) -> Option<String> {
+    let transport = macos_helpers::get_device_transport_type(device_id).ok()?;
+
+    let transport_str = if transport == transport_types::BUILT_IN {
+        "built-in"
+    } else if transport == transport_types::USB {
+        "usb"
+    } else if transport == transport_types::BLUETOOTH
+        || transport == transport_types::BLUETOOTH_LE
+    {
+        "bluetooth"
+    } else if transport == transport_types::HDMI
+        || transport == transport_types::DISPLAY_PORT
+    {
+        "hdmi"
+    } else if transport == transport_types::THUNDERBOLT {
+        "thunderbolt"
+    } else if transport == transport_types::FIREWIRE {
+        "firewire"
+    } else if transport == transport_types::VIRTUAL {
+        "virtual"
+    } else if transport == transport_types::AGGREGATE {
+        "aggregate"
+    } else {
+        "unknown"
+    };
+
+    Some(transport_str.to_string())
+}
+
+// ---- Non-macOS stubs ----
+
+/// Query supported sample rates (stub for non-macOS)
+#[cfg(not(target_os = "macos"))]
+pub fn query_supported_sample_rates(_device_name: &str) -> Result<Vec<u32>, String> {
+    Ok(Vec::new())
+}
+
+/// Get the current nominal sample rate (stub for non-macOS)
+#[cfg(not(target_os = "macos"))]
+pub fn get_nominal_sample_rate_by_name(_device_name: &str) -> Result<u32, String> {
+    Err("CoreAudio is only available on macOS".to_string())
+}
+
+/// Set the nominal sample rate (stub for non-macOS)
+#[cfg(not(target_os = "macos"))]
+pub fn set_nominal_sample_rate_by_name(
+    _device_name: &str,
+    _target_rate: u32,
+) -> Result<(), String> {
+    Err("CoreAudio is only available on macOS".to_string())
+}

crates/qbz-audio/src/lib.rs

@@ -34,6 +34,7 @@ pub mod alsa_backend;
 #[cfg(target_os = "linux")]
 pub mod pulse_backend;
 pub mod alsa_direct;
+pub mod coreaudio_direct;
 pub mod analysis;
 pub mod analyzer_tap;
 pub mod diagnostic;

src-tauri/Cargo.lock

@@ -1077,6 +1077,19 @@ dependencies = [
  "objc2-core-foundation",
 ]
 
+[[package]]
+name = "coreaudio-rs"
+version = "0.14.0"
+source = "git+https://github.com/afonsojramos/coreaudio-rs.git?branch=feat%2Fdevice-helpers#ce3fec9bce0b43ece78bb8801c87be9889e5710e"
+dependencies = [
+ "bitflags 2.11.0",
+ "libc",
+ "objc2-audio-toolbox",
+ "objc2-core-audio",
+ "objc2-core-audio-types",
+ "objc2-core-foundation",
+]
+
 [[package]]
 name = "cpal"
 version = "0.17.1"
@@ -1084,7 +1097,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "5b1f9c7312f19fc2fa12fd7acaf38de54e8320ba10d1a02dcbe21038def51ccb"
 dependencies = [
  "alsa 0.10.0",
- "coreaudio-rs",
+ "coreaudio-rs 0.13.0",
  "dasp_sample",
  "jni",
  "js-sys",
@@ -4496,6 +4509,7 @@ version = "0.1.0"
 dependencies = [
  "alsa 0.9.1",
  "async-trait",
+ "coreaudio-rs 0.14.0",
  "dirs 5.0.1",
  "ebur128",
  "log",