molluskandClaude Opus 4.8
039c34322c
The playback stream was negotiated with a ~256ms (12288-frame) maxsize buffer. The sink drains the graph quantum (1024 frames) per cycle, so one of our buffers lasted ~12 cycles and `process` was called only ~4x/sec, each time asking us to fill all 12288 frames -- far more than the 200ms (9600-sample) playout ring could ever hold. So ~half of every buffer was silence-fill: a steady ~46% underrun, audible as constant crackle. This is a consumer-side buffer-size bug, upstream of production pacing, which is why earlier mixer-pacing attempts never moved the numbers. Fix: pass an explicit SPA_TYPE_OBJECT_ParamBuffers param on connect, pinning buffer size to one 1024-frame quantum (2048 bytes mono S16LE). PipeWire now hands us a quantum-sized buffer ~47x/sec, the ring satisfies every callback, and slice.len()/stride equals the quantum so we never over-pull. A node.latency hint is added too (not load-bearing on its own -- the hint alone changed nothing; the Buffers param is the fix). Note: pipewire 0.9.2 only exposes feature v0_3_32, so Buffer::requested() is unreachable -- pinning the buffer size is the available lever. Verified with the probe (quantum=1024, 47 cb/s, underrun +0 steady) and by ear: clean 440Hz tone, no clicks. Local playout path only -- not yet verified on a live two-peer call. Also in this commit (the investigation scaffolding that proved it out): - Fill-paced mixer: production tracks the hardware clock via a shared exact ring-occupancy gauge (Arc<AtomicUsize>) kept near PLAYBACK_TARGET_SAMPLES, replacing the fixed 20ms timer that beat against the 1024 quantum. - src/bin/audio_probe.rs: drives a sine through the real start_playback path with no network/mic, for isolating the local output stage. - playout-health logging: quiet in normal use (logs only on underrun/ dropped > 0); set PEERSPEAK_AUDIO_VERBOSE=1 for the per-second heartbeat (audio_probe sets it automatically). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>