fix: support Bluetooth audio input devices (AirPods)#70
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On macOS, Bluetooth devices like AirPods connect in A2DP mode (output only). The microphone requires a switch to HFP/SCO, which cpal's low-level AudioUnit HAL doesn't always trigger. Changes: - Add CoreAudio activation hook (activate.rs) that re-sets the default input device via AudioObjectSetPropertyData to nudge macOS into establishing the Bluetooth SCO link for microphone input - Add dead-stream detection in ensure_warm() using a callback counter so disconnected devices are detected and the stream is re-opened - Log device name, sample rate, channels, and format when opening a device for easier debugging of audio issues - Log audio RMS in VAD when speech detection fails, and log when transcription produces empty text (previously silent)
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Problem
AirPods (and other Bluetooth devices) connected to macOS would deliver silence when used as the default audio input device. The microphone was never activated because cpal's low-level AudioUnit HAL doesn't trigger the Bluetooth A2DP → HFP profile switch that enables the mic.
Root Cause
macOS Bluetooth devices start in A2DP mode (high-quality output only). The microphone requires HFP/SCO mode, which higher-level Apple frameworks (
AVCaptureSession) trigger automatically, but cpal's AudioUnit HAL does not.Fix
activate.rs): Re-sets the default input device viaAudioObjectSetPropertyData, which nudges macOS into establishing the Bluetooth SCO link. Platform-gated (#[cfg(target_os = "macos")]), no-op elsewhere, no new dependencies.ensure_warm()now probes callback activity before each recording. If the device disconnected (e.g. Bluetooth dropped), the stream is re-opened on the current default device.Testing