Adds one Information-level structured log per HLS tune-in cold-start so the
real driver breakdown can be measured on prod before optimizing the transcode
pipeline (measure-before-optimize). Log-only; no transcode behavior change.
- WaitForPlaylistSegments returns a PlaylistSegmentsResult: Phase A (process
startup -> playlist exists) vs Phase B (segment fill), segments reached,
deadline-expired.
- StartFFmpegSessionHandler emits one summary: total = setup + startup + fill,
plus cleanly-detectable feature flags (subtitle burn-in, hwaccel family).
- ColdStartFeatures: pure, unit-tested args->features helper (14 cases).
Watermark / HDR->SDR / image-subtitle burn-in are deliberately not flagged
(all reduce to overlay= in the args, indistinguishable); the full ffmpeg
arguments remain available at Debug.
Refs #350 (instrumentation slice; optimization deferred pending real data).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
