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feat(hls): pre-segmentación delantada — 2 s segments + async session start (0.9.10)

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First-frame latency drops by another 1-2 s on cold-cache plays:

1. HLS segment duration halved from 4 s to 2 s. seg-0 lands in ~half
   the wait time — the player paints the first frame as soon as it
   arrives. Software encodes on 4K go from ~3 s wait to ~1.5 s; HW
   encoders shave ~0.5 s. Trade-off: 2× segment count per source
   (~3600 segments for a 2 h movie instead of ~1800), but each is
   half the size on disk. Within HLS spec — Apple recommends 6 s, but
   2 s is valid; LL-HLS uses 1-2 s.

2. Cache from 0.9.9 self-heals: cached entries used 4 s segments;
   VerifyComplete now expects a different highest segment index and
   invalidates them, triggering a re-encode on next play. No manual
   cleanup needed.

3. OnStreamSession daemon callback now runs StartHLSSession in a
   goroutine. Sync HTTP responses return immediately (~50 ms instead
   of waiting for the ~0.3-1 s ffprobe). Other pending actions in
   the same sync cycle (new tasks, deletes) no longer wait for the
   transcoder warmup. Browser HEAD probes already have a 30 s retry
   budget that covers the brief gap between playerSessionRegistry.add
   and streamSrv.HLS().Register.

Helpers added (engine.segmentDurationFor / segmentStartSec /
segmentCountForDuration) so a future short-first-segment variant or
non-uniform layout can slot in without touching every call site.

Internal: -hls_init_time was investigated but discarded — ffmpeg's
implementation treats it as a min duration, not a target, so it
couldn't deliver a uniformly 2 s first segment on top of a 4 s
steady state. Uniform 2 s is simpler and gets the same first-frame
win.
This commit is contained in:
Deivid Soto 2026-05-27 11:36:41 +02:00
parent bf8ed0d928
commit 0b2462c82a
5 changed files with 96 additions and 27 deletions
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25
internal/cmd/daemon.go
View file

@ -580,14 +580,23 @@ func runDaemonStart() error {
Transcode: tcRuntime,
Cache: hlsCache,
}
hsess, err := engine.StartHLSSession(hlsCtx, hlsCfg)
if err != nil {
playerSessionRegistry.remove(sess.SessionID)
hlsCancel()
log.Printf("[hls %s] start failed: %v", agent.ShortID(sess.SessionID), err)
return
}
streamSrv.HLS().Register(hsess)
// StartHLSSession runs ffprobe (15 s cap, typical 0.3–1 s) before
// returning. Doing this synchronously inside the sync handler holds
// the next sync HTTP cycle until ffprobe is done, so any other
// pending actions (new tasks, deletes) wait too. Hand it off so
// the sync loop returns immediately — browser HEAD probes already
// have a 30 s retry budget that absorbs the gap until
// `streamSrv.HLS().Register` lands.
go func() {
hsess, err := engine.StartHLSSession(hlsCtx, hlsCfg)
if err != nil {
playerSessionRegistry.remove(sess.SessionID)
hlsCancel()
log.Printf("[hls %s] start failed: %v", agent.ShortID(sess.SessionID), err)
return
}
streamSrv.HLS().Register(hsess)
}()
}
// Periodic DHT node persistence (every 5 min)