Two-phone production logs at commit 6e4df4a (run 18:37) showed the
listener-side cliff still hits at ~16 s of streaming (51 groups
delivered, sender continued to seq=80 = ~6 s of audio lost at the
tail before the receiver recycled). Recycling alone can't fix this
— it only spaces the pain out. The user wants no audio drops mid-
transmission, period. The leverage is to keep the relay's
per-subscriber forward queue from filling at all.
The cliff is rate-limited per uni-stream-creation, not per byte or
per frame — moq-rs's `serve_group` task pool can't drain new
`open_uni().await`s fast enough at high stream rates. Cutting the
stream creation rate cuts the cliff window proportionally:
framesPerGroup | streams/sec @ 50 fps | observed cliff window
---------------+------------------------+----------------------
1 | 50 | ~3 s (commit d6517cf)
5 | 10 | ~13 s
10 | 5 | ~16 s (commit 6e4df4a)
50 | 1 | not reached in
`fpg-all` sweeps
100 | 0.5 | never observed
Bumping default to 50 (1 s of audio per uni stream, 1 stream/sec)
puts us in the regime where the relay's queue does not measurably
fill. `fpg-all` (100 frames in a single group) routinely delivers
100/100 in production sweeps, so 50 is well clear of the cliff
edge. We pick 50 not 100 because:
- Late-join gap is bounded by group size — a listener joining
mid-broadcast waits one group boundary for the first frame.
1 s is within the ~250 ms AudioTrack jitter buffer +
`ROOM_PLAYER_PREROLL_FRAMES = 5` audio-buffer envelope; 2 s
starts to be perceptible.
- QUIC stream RST drops the whole group on full reset. 1 s of
skip on rare RST is bearable; 2 s is a noticeable seam.
- Sender encode latency stays at 1 s — no worse than the
natural buffering audio rooms already do for jitter.
Belt-and-suspenders: also tighten the cliff-detector's silence
threshold from 4 s to 2.5 s. Healthy streams now arrive every ~1 s
(one `drainOneGroup` FIN per group), so 2.5 s of silence is
unambiguously past two missed group cycles. Catches a still-
possible cliff event ~1.5 s earlier, shaving the audible gap from
~6 s (4 s detection + 2 s reconnect) to ~4.5 s if recovery is
needed at all.
Tests: existing `framesPerGroup`-explicit interop scenarios
(`fpg5`, `fpg20`, `fpg-all`) are unaffected — they pass an
explicit value and don't read the default. `CliffDetectorTest`
boundary cases updated to the new 2.5 s threshold;
`returnsAllStalledSpeakersAtOnceMixedWithFreshOnes` re-spaced its
fixture so charlie's 1.5 s frame age stays under threshold while
alice/bob's 4 s ages exceed it. 12/12 pass.
Claude
a36ccb5692