macOS realtime audio was suffering buffer underruns on CoreAudio's VPIO
output callback. Root cause was twofold: AudioHandler was decoded under
a Mutex held across the realtime callback, and the render path
hard-coded mono i16 output regardless of the channel count the
callback actually exposed (CoreAudio occasionally hands the callback
stereo or quad output buffers, in which case writing only every Nth
sample produced silence + clicks).
This change brings macOS in line with the lock-free Android audio
architecture introduced for output stutter elimination:
* chanora_audio: AudioPacket / AudioCommand / AudioEventQueue
(previously gated to `target_os = "android"`) are now compiled on
macOS too. The decode loop in AudioEngine pushes inbound packets
into the queue; the VPIO render callback owns AudioHandler outright
and drains the queue, so the realtime thread never blocks on a
cross-thread mutex. set_client_volume also routes through the
command queue on macOS instead of locking the handler.
* voice_render.rs: new downmix_stereo_f32_to_interleaved_i16 helper
downmixes stereo f32 from AudioHandler to mono i16 and replicates
that mono sample across every output channel the callback exposes.
The existing downmix_stereo_f32_to_mono_i16 helper is retained for
iOS, where VPIO is reliably configured for single-channel output
via the AudioUnit stream format we pin at unit-create time.
Compile-gated to ios + test so the macos build doesn't warn on
dead code.
* ios_voice_unit.rs: render callback reads data.channels from the
args struct and forwards it to the new interleaved helper, so the
macOS path tolerates whatever channel count CoreAudio assigns. A
level decimation counter avoids running sqrt+log10 on every
callback (~93 Hz) when the Flutter consumer only reads at 30 Hz;
same regression class as the capture-side fix already in engine.rs.
* mobile_voice_backend.rs: VoiceAudioParams now carries
event_producer on macOS, and the AudioHandler is no longer wrapped
in Arc<Mutex<…>> on macOS because ownership moves into the render
callback. iOS keeps Arc<Mutex<…>> because its callback design
shares the handler with the decode task.
* lib.rs: audio_event_queue module is now compiled on macOS in
addition to android.
apps/chanora_flutter/lib/main.dart wraps the home tree in a Stack and
overlays AudioDebugStatsPanel on macOS so the live engine counters
(callback rate, drift, queue depth) used to diagnose the underrun are
visible while iterating on this code. iOS and other platforms are
unaffected.
apps/chanora_flutter/macos/Frameworks/chanora_bridge.framework binary
is rebuilt with these changes so flutter run on macOS picks up the new
realtime path without requiring developers to rebuild the Rust crate
locally. cargo check -p chanora_audio passes on macOS host.
Edison Jwa
23bfddb6b4