Changes the audio subsystem from hw: (direct hardware access) to plughw:
(plugin layer with rate conversion) to enable configurable sample rates.
Changes:
- Update ALSA build to include plug,rate,linear,copy plugins
- Change device names from hw: to plughw: in C and Go code
- Remove 48kHz hardcoding for HDMI audio output
- Keep USB at 48kHz since hardware is fixed at that rate
- Update all comments to reflect plughw usage
Technical details:
- hw: devices bypass all ALSA plugins and require exact hardware rate match
- plughw: devices enable the ALSA plugin layer for automatic rate conversion
- Hardware still receives at native rate (48kHz), resampling happens in userspace
- HDMI can now use 8k/12k/16k/24k/48kHz, USB remains at 48kHz
- NEON-optimized resampling provides good performance on Cortex-A7
Requires rebuilding ALSA library with updated plugin configuration.
- Replace helper function in getAudioConfig with explicit validation
- Consolidate audio default application in LoadConfig
- Streamline relay retry logic with inline conditions
- Extract closeFile and openHidFile helpers in USB gadget
- Simplify setPendingInputTrack pointer handling
- Improve error handling clarity in startAudio and updateUsbRelatedConfig
- Clean up processInputPacket mutex usage
Alex P