At 5120x1440 the stream froze on a ~2s cadence. Two compounding causes (confirmed by a
profiling pass + adversarial review):
1. Periodic IDR every 2s (set_gop(fps*2)). A keyframe at 5K is ~20-40x a P-frame — a
recurring multi-millisecond encode+packetize+send spike. Fix: infinite GOP (gop_size=-1),
one IDR at stream start, P-frames only; forced-idr makes a client recovery request (RFI via
request_keyframe) emit an IDR on demand — the Moonlight/Sunshine low-latency model.
2. Two pacing timers summing on the capture/encode thread: a per-packet thread::sleep pacer
(spread a frame's packets across a whole frame interval) PLUS a backstop sleep on top, so
every frame cost 1-2x the interval and the big IDR blew through it (the 2->120 oscillation).
Fix: delete both; send at line rate and drive cadence from a single absolute deadline.
(Proper microburst pacing belongs on a dedicated send thread — a follow-up.)
Also: honor the client's fps (pacing clamp 60->240) and add an env-gated (LUMEN_PERF)
per-stage timing log (enc/pkt/send µs + unique-vs-reencoded frames + max packet burst) for
diagnosing the remaining throughput ceiling. Verified live: freeze gone at 5120x1440.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
enricobuehler
0e1853e070