Two Linux mission-audio fixes for Project Sylpheed (audio played in
intro/menu but died when a mission finished loading, never returning):
- alsa_audio_driver: when the guest stalls (mission "Preparing for Sortie"
load) and the ring buffer empties, feed silence to keep the PCM alive
instead of sleeping. Previously the small buffer drained, XRUN'd, and
playback never recovered (matches the known "audio muted permanently").
- xconfig: make the guest speaker config a cvar (guest_audio_flags,
default Digital Stereo) instead of hardcoded Dolby Digital surround.
(The practical fix on this box also needed log_mask=13 to stop kernel log
spam starving the audio pipeline during missions — config, not code.)
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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