Bug hunt 2026-09, items 8 and 12 — the two things the Plex player was measurably
lying about.
Item 8: picking a subtitle track showed nothing for a long time, and the reported
workaround was to stop/start until it suddenly worked. Measured on prod against a
17.06 GB MKV with two embedded SubRip tracks:
full pass, one track 154 s
full pass, both tracks in ONE run 111 s
-c:s copy (no WebVTT conversion) 143 s
from 1:00:00 to the end of file 66 s
a 630 s window at 1:00:00, both 8 s
So the conversion was never the cost: ffmpeg streams every byte of the container
between its seek point and its stop point, and the array delivers ~140 MB/s. The
only lever is reading less. Three changes follow from that:
* a window around the playhead is extracted and published FIRST (seconds), and
the full pass completes behind it;
* every embedded text track rides that same single read — picking Hungarian used
to cost a full pass and then switching to English cost another one;
* none of it happens inside a request any more. The endpoint answers 202 while a
background worker extracts, the player polls /status (carrying its position, so
the window follows the viewer), and one ffmpeg run finally has a timeout.
-copyts is deliberately absent from a windowed pass: with it ffmpeg ignores -t and
reads the whole container anyway (measured — a [0, 600 s] window still took the
full 145 s), so a window comes back on a zero-based clock and is shifted to
absolute time here. Cached tracks written by older builds have no coverage sidecar
and count as complete, so nothing is re-extracted after the upgrade.
The <track> is no longer mounted before the server has something to put in it; a
"Preparing subtitles: …" notice stands in, and a track that can never be shown says
why instead of leaving the viewer to conclude the picker does nothing.
Item 12: "Bitrate" read a constant 211 kbps on every remux, because it was the
master playlist's BANDWIDTH — which ffmpeg derives from the one stream whose rate
it knows, the -b:a 192k AAC track, plus 10%. It is a measurement now: bytes per
second of MEDIA from hls.js FRAG_LOADED, accumulated per fragment type and summed
(a multi-audio session's video and audio renditions cover the same media seconds,
so pooling them would report half the truth), and an honest dash until the first
fragment lands. The panel also finally names the audio and subtitle track in play.
Verified in the browser against the real Plex library, and every new test
mutation-checked.
Upgrade mode-3's 10-bit/HDR branch from "route to software libx264" (BUG 1's
behaviour) to a full-GPU pipeline: VAAPI decode → OpenCL tonemap (hable,
HDR10/HLG → bt709 SDR nv12) → h264_vaapi. Gen 9.5 (UHD 630) can't tonemap in
the VAAPI VPP (tonemap_vaapi fails), so OpenCL is the only HW route — proven on
the prod iGPU at ~4.2x realtime, ~1 CPU core.
- stream.py: `_select_encode` returns (hw, tonemap); a 10-bit/HDR HW-decodable
source picks the tonemap graph when the OpenCL runtime is present, else drops
to software. `_opencl_present` gates on a registered ICD. `_venc_opts` /
`_hwaccel_in_opts` gain the tonemap variant (named vaapi+opencl devices,
`-filter_hw_device ocl`, hwmap→tonemap_opencl→hwmap reverse). `_want_hw` kept
as the hw-half wrapper. The runtime HW→SW fallback still backstops a session
that emits no segment.
- Dockerfile: add the Intel NEO OpenCL runtime (intel-opencl-icd). It was removed
from Debian trixie, so it's pulled from bookworm (22.43 still supports Gen 9.5;
the .deb runs on the trixie base — verified live). Harmless without /dev/dri.
- route + FE: thread `tonemap` through the session response; the stats overlay
mode row reads "transcode · GPU · HDR→SDR" for the tonemap path.
- tests: tonemap command branch, the (hw, tonemap) selection matrix (auto/on ×
8-bit/10-bit × opencl), start_session tonemap wiring, and the fmtMode tag.
Eight verified findings from the sprint deep-review:
- Transcode cap: _enforce_cap now counts only transcode sessions, so a
live remux (stream-copy) stream can no longer be LRU-evicted mid-play —
matching the config comment + the HU/EN Config hint that promise remux
is uncapped.
- Player Back: the browser/mouse Back interceptor (BackClose) now also
mounts for the stats overlay and up-next card, so Back closes them first
instead of ejecting the whole player (keyboard/Esc already did).
- Honest cold-start: loadSession clears sessionIsTranscode up front, so a
transcode->direct/remux switch no longer flashes a stale "Preparing
stream..." during the session request.
- Stats overlay a11y: the close (X) buttons in the stats, help and info
overlays now read as "Close"/"Bezaras" (new plex.player.close key), not
"Back"; dropped aria-live from the per-second stat grid so a screen
reader is not flooded with telemetry.
Tests: route-level transcode routing (transcode item -> HLS re-encode
session, remux stays copy, direct opens none); start_session threading the
preset/crf/max_height knobs + hw/preexec into the ffmpeg argv; UpNextCard
countdown auto-advance, Play-now, Cancel and the S?-E? heading fallback.
Also brings UpNextCard.tsx / plexStats.ts / plexStats.test.ts to prettier.
Surface the transcode session's runtime facts in the player. The session
response's transcode/hw flags now thread through: the stats overlay's mode row
reads "transcode · GPU" (VAAPI) or "transcode · CPU" (libx264) — the at-a-glance
confirmation of which S1 path engaged — and the initial-load overlay says
"Preparing stream…" instead of "Loading…" for a transcode session, since its
first segment is genuinely slower than a remux and shouldn't read as a hang.
fmtMode (pure, unit-tested) appends the encoder only for a transcode with a known
encoder. i18n HU/EN for the new preparing label. Browser-UAT'd on the XviD
fixture: mode row reads "transcode · CPU" live (software, no render node here).
Add a toggleable stats overlay to the Plex player: active mode
(direct/remux/transcode), transport, resolution, codec, bitrate, HLS level,
dropped frames, buffer-ahead, session offset and position — sampled once a
second off the live videoRef + hlsRef (no data layer). Non-modal corner panel,
aria-live polite, dismissable; toggled with 'd', a gauge control-bar button, or
its X. Number-crunching lives in a pure, unit-tested plexStats module. Doubles
as the S1 transcode-verification surface. i18n HU/EN.
peter