WASAPI: Use ActivateAudioInterfaceAsync with virtual device IDs for default devices

.github/workflows/cpal.yml

@@ -320,8 +320,6 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - windows-version: "0.59.0"
-          - windows-version: "0.60.0"
           - windows-version: "0.61.3"
           # Skip 0.62.x since we already test current version in test-native
     name: test-windows-v${{ matrix.windows-version }}
@@ -349,6 +347,12 @@ jobs:
           # Use cargo update --precise to lock the windows crate to a specific version
           cargo update --precise ${{ matrix.windows-version }} windows
 
+          # Remove and re-add `windows-core` to force Cargo to re-resolve it
+          # I'd prefer a more surgical approach, but things get complicated once multiple `windows-core`
+          # versions are in play
+          cargo rm --target='cfg(target_os = "windows")' windows-core
+          cargo add --target='cfg(target_os = "windows")' windows-core@*
+
           # Verify the version was locked correctly
           echo "Locked windows crate version:"
           cargo tree | grep "windows v" || echo "Windows crate not found in dependency tree"

Cargo.toml

@@ -10,11 +10,21 @@ edition = "2021"
 rust-version = "1.70"
 
 [features]
+default = ["wasapi-virtual-default-devices"]
+
 asio = [
     "asio-sys",
     "num-traits",
 ] # Only available on Windows. See README for setup instructions.
 
+# Enable virtual default devices for WASAPI. When enabled:
+# - Audio automatically reroutes when the default device changes
+# - Streams survive device changes (e.g., plugging in headphones)
+# - Requires Windows 8 or later
+#
+# Disable this feature if supporting Windows 7 or earlier.
+wasapi-virtual-default-devices = []
+
 # Deprecated, the `oboe` backend has been removed
 oboe-shared-stdcxx = []
 
@@ -31,7 +41,12 @@ clap = { version = "4.5", features = ["derive"] }
 # versions when bumping to a new release, and only increase the minimum when absolutely necessary.
 # When updating this, also update the "windows-version" matrix in the CI workflow.
 [target.'cfg(target_os = "windows")'.dependencies]
-windows = { version = ">=0.58, <=0.62", features = [
+# The `implement` feature was removed in windows-0.61, which means that we can't
+# use older versions of the `windows` crate without explicitly activating `implement`
+# for them, which will cause problems for >=0.61.
+#
+# See <https://github.com/microsoft/windows-rs/pull/3333>.
+windows = { version = ">=0.61, <=0.62", features = [
     "Win32_Media_Audio",
     "Win32_Foundation",
     "Win32_Devices_Properties",
@@ -44,6 +59,8 @@ windows = { version = ">=0.58, <=0.62", features = [
     "Win32_Media_Multimedia",
     "Win32_UI_Shell_PropertiesSystem",
 ] }
+# Explicitly depend on windows-core for use with the `windows::core::implement` macro.
+windows-core = "*"
 audio_thread_priority = { version = "0.34.0", optional = true }
 asio-sys = { version = "0.2", path = "asio-sys", optional = true }
 num-traits = { version = "0.2.6", optional = true }

src/host/wasapi/com.rs

@@ -4,7 +4,9 @@ use super::IoError;
 use std::marker::PhantomData;
 
 use windows::Win32::Foundation::RPC_E_CHANGED_MODE;
-use windows::Win32::System::Com::{CoInitializeEx, CoUninitialize, COINIT_APARTMENTTHREADED};
+use windows::Win32::System::Com::{
+    CoInitializeEx, CoTaskMemFree, CoUninitialize, COINIT_APARTMENTTHREADED,
+};
 
 thread_local!(static COM_INITIALIZED: ComInitialized = {
     unsafe {
@@ -50,6 +52,14 @@ impl Drop for ComInitialized {
     }
 }
 
+/// RAII for COM-originating strings that need to be freed with `CoTaskMemFree`.
+pub struct ComString(pub windows::core::PWSTR);
+impl Drop for ComString {
+    fn drop(&mut self) {
+        unsafe { CoTaskMemFree(Some(self.0.as_ptr() as *mut _)) }
+    }
+}
+
 /// Ensures that COM is initialized in this thread.
 #[inline]
 pub fn com_initialized() {