Asked for directly, right after the client-side <track> redesign closed
every *text* subtitle case: PGS/VobSub/DVB subtitles (Blu-ray/DVD rips)
are bitmaps, not text - there's nothing for Emby's Stream.vtt conversion
to extract, so a native <track> fundamentally can't render one. Rather
than keep asking Emby's own transcode to burn these in (the exact thing
that kept failing in earlier sessions - missing fontconfig, then an
unrelated "Error starting ffmpeg"), this runs ffmpeg ourselves: a PGS
stream decodes like a second video track, and ffmpeg's `overlay` filter
composites it directly - no text rendering, no libass, no fontconfig
anywhere in this path.
One shared stream per PARTY, not per viewer - explicitly asked for after
the initial plan: every member plugs into the exact same server-emitted
stream, mirroring "host drives, everyone follows" rather than a
per-viewer model. Picking a burn-in subtitle is therefore a host-only,
party-wide choice, like play/pause/next already are.
- server/src/services/TranscodeService.ts (new): one ffmpeg session per
partyId. getOrStartSession negotiates PlaybackInfo (via the new
CatalogService.getMediaSource), converts Emby's absolute
MediaStreams[].Index into ffmpeg's type-relative 0:s:N/0🅰️N
(absoluteToRelativeIndex - pure, unit-tested), and spawns ffmpeg
against Emby's own direct/static file endpoint (TODO(verify) - no
Emby server reachable from this dev environment, see the function's
own comment). Output is real progressive HLS to a temp dir, served by
two new routes that poll briefly for the next file. endSession/
reapIdleSessions handle teardown; PartyService's destroy path and
advanceQueue both end a party's session immediately, the idle sweep
is the backstop.
- server/src/services/PartyService.ts: Party/PartyPublicState gain
burnInSubtitleIndex/burnInAudioIndex (null together = no burn-in);
advanceQueue clears them (a new item's indices mean nothing on the
old one).
- server/src/realtime/SocketGateway.ts: new host-only "setBurnInSubtitle"
handler broadcasting "burnInChanged" - same shape as "next"/
"itemChanged".
- server/src/services/CatalogService.ts: new getMediaSource() (id/
container/streams together - what TranscodeService needs); extended
the local PlaybackInfoResponse type with Container.
- server/src/Logger.ts: new Logger.transcode().
- server/src/index.ts: GET /api/catalog/burn/:partyId/master.m3u8 and
.../:segment (membership-checked, same pattern as the party REST
routes); a dedicated idle-reap interval for TranscodeService.
- server/Dockerfile: `apk add ffmpeg` in the runtime stage - no font
packages needed, unlike Emby's own text-subtitle burn-in.
- client/src/api/party.ts, client/src/api/embyApi.ts: setBurnInSubtitle/
onBurnInChanged on PartyConnection, burnInStreamUrl().
- client/src/views/player/Player.{html,css,ts}: the subtitle picker's
image-track options go from unconditionally disabled to host-only
selectable, labeled to say picking one restarts the stream for
everyone. Every member (host included) only ever reacts to the
resulting "burnInChanged" broadcast - never applies a pick
optimistically, same discipline the rest of the player already uses.
Audio/quality are disabled while a burn-in is active (one fixed
encode); a follower's subtitle select is disabled too (nothing left
for them to meaningfully pick).
- server/test/transcodeService.test.ts (new): absoluteToRelativeIndex,
session start/reuse/replace, endSession, reapIdleSessions -
child_process.spawn mocked via a small explicit test seam
(setSpawnForTesting), never invoking a real ffmpeg binary.
- server/test/socketGateway.test.ts, partyService.test.ts,
catalogService.test.ts: host-only gating + broadcast for
setBurnInSubtitle, advanceQueue's reset, toPublicState exposing the
new fields, getMediaSource.
- docs/architecture.md, README.md: design + an explicit "assumptions to
verify" note (the direct-source URL shape, first and foremost).
Verified: full typecheck+test+build on both projects (56/56 server
tests). No Emby server or ffmpeg binary is reachable from this dev
environment, so the actual command against a real PGS file is
unverified - flagged explicitly in the docs, same "TODO(verify)" spirit
already used elsewhere in this codebase for an Emby response shape that
can't be checked locally.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Nicolas
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