The Plex player stalled ~2s a few seconds into every auto-advanced next
episode. Root cause: each auto-advance spins up a cold ffmpeg HLS remux
session, and for a fresh start (start_s==0) start_session returned
immediately with zero buffer — hls.js drained the first segment, then
rebuffered waiting for the still-warming ffmpeg to write the next one.
Once ffmpeg gets ahead (stream-copy is faster than realtime) it never
stalls again.
- stream.py: before reporting a session ready, wait for the first
_WARMUP_SEGMENTS (3) video segments to exist — the seg0 wait is now
unconditional (was start_s>0 only) and warm-up runs for all starts.
Best-effort and bounded: stop at the first segment not ready in time.
- PlexPlayer.tsx: a loading/buffering spinner. The existing overlay only
covered the INITIAL load (!ready); add a `buffering` state driven by the
video's waiting/stalled/seeking (set) and playing/canplay/seeked/pause
(clear) events so a mid-playback stall or in-flight seek reads as
"loading" instead of a frozen frame, and surface a fatal loadError even
once playback has started. Spinner uses the shared Loader2.
Merges roadmap E6·item1 (spinner while loading/seeking) into this fix,
since the server-side warm-up deliberately holds ready a beat longer.
Tests: 3 new in test_plex_stream.py (warm-up waits for the first few
segments; stops at the first missing one; no warm-up when seg0 never
arrives). Gate: backend pytest 460 (Docker lane), FE tsc/lint/knip/
prettier + vitest 483.
peter
12d9561ba1