watchparty/README.md

# Watch Party for Emby

A standalone web app for watching the same title, in sync, with other users
of the same Emby server. It reads your Emby catalog and streams your Emby
media, but it's its own app with its own player — not an Emby plugin.

See [docs/architecture.md](docs/architecture.md) for the full design,
including why this replaced an earlier Emby-plugin attempt (still in
[src/WatchParty/](src/WatchParty/) for reference — see below).

## How it works

1. Sign in with your Emby account (just username/password — the server
   address is fixed server-side, see Deploying below).
2. A sidebar lists your Emby libraries (movies, TV, music, music videos,
   playlists if you have any — anything else Emby might have, like
   photos or a boxset collection, isn't shown); the home page shows every ongoing
   watch party live (host, how long it's been running, member count) plus a
   "recently added" row per library, Emby-style. No join codes — if a party
   is running, it's already on the list, updating in real time.
3. Pick a movie/episode tile and hit "Lancer une watch party" (or drill into
   a Series' seasons/episodes first) — you become the host — or hit
   "Rejoindre" on any party already listed on the home page. Already
   connected to that same party from another device? You're asked to
   confirm before it gets disconnected — reconnecting from the same
   device (a reload, a second tab) never asks.
4. The host's play/pause/seek drives everyone else's player automatically;
   starting from an episode queues the rest of the series so the host can
   just hit "Épisode suivant" instead of restarting a party each time. If
   the host leaves, the party hands off to another member automatically
   (their player unlocks live, no reload needed) — only closing once
   everyone's gone. Everyone also shares the exact same stream from
   Emby — one transcode per party, not one per person — so the host's
   language/quality pick applies for the whole party too.
5. Everyone present shows up as a small avatar overlay on the video (their
   initials, on the player itself). If you're not the host, a small
   toolbar lets you ask the host to pause or resume — everyone sees the
   request, including the host, without needing chat.
6. Subtitles are a host-only, party-wide pick too, like the
   language/quality pick above — the host picks one (or "Aucun") and
   everyone's player follows. Any text-based track just renders
   natively in each viewer's own browser, in sync (no reload, no extra
   server load — only *which* one is synced). A Blu-ray/DVD-style image
   subtitle (PGS/VobSub/DVB) is different — picking one has this app's
   own ffmpeg burn it into the video, shared live by everyone in the
   party, which does restart the stream for everyone since the video
   itself changes.
7. Music works differently, on purpose: pick a track (browsing Artist →
   Album → Track) to start a listening party. There's no host for
   playback — anyone can add more tracks to the shared queue at any time,
   anyone can pause/resume, and skipping the current track needs a
   majority vote from whoever's currently listening. The player itself is
   a persistent bar docked at the bottom of the screen, not a page — the
   sidebar and the rest of the app stay fully usable while it plays, so
   adding more tracks is just browsing to an album and clicking a track
   (its button reads "Ajouter à la file" instead of "Écouter ensemble"
   once a party's already going). Starting or joining a video watch party
   always leaves the listen party first — the two don't run at once.
8. A playlist works the same idea as a series: open it to see what's
   inside, then "Lancer cette playlist" starts one party pre-loaded with
   everything in it — a video queue if it's movies/episodes, or the
   participative music queue if it's tracks.
9. While you're in a party, your own progress is quietly pushed back to
   your own Emby account (resume position, last-played state) — so
   opening Emby's own app afterward reflects what you actually watched
   or listened to, not just this app's own memory of it.

Everything — catalog, images, video, audio, sync — flows through this
app's own backend, which proxies whatever it needs from Emby server-side.
The browser never talks to Emby directly and never holds an Emby access
token; it only ever has a session cookie for this app.

## Status

Login, and the rendering/navigation logic for every page (sidebar, home,
library, series, artist/album, both players), have been exercised end to
end (login against the real Emby server with intentionally-wrong
credentials; the pages against mocked API responses; the music queue's
timer/vote/pause logic against the real server modules directly - no Emby
involved there at all). See
[docs/architecture.md](docs/architecture.md#assumptions-to-verify) for
exactly what that does and doesn't confirm — the real Emby response shapes
this now depends on (library `CollectionType`, seasons/episodes, artists/
albums/tracks, `PlaybackInfo`'s media streams) and actual HLS playback
(video or audio) are still unverified.

The TypeScript rewrite itself is separately verified: both projects
type-check in strict mode, the server has a real automated test suite
(`server/test/*.test.ts`, Node's built-in test runner, see Running
locally below) covering the party lifecycle, the music queue's
timer/vote/pause behavior, the socket protocol, and the catalog/streaming
overrides, and the compiled+bundled client was driven through every page
and both players end to end (mocked network/Socket.IO) in a real browser.
CI (Forgejo Actions) runs that same typecheck+test+build sequence on
every push and gates the Docker image publish on it passing — see
[docs/architecture.md](docs/architecture.md#continuous-integration).
**Not verified**: an actual `docker build` of the new multi-stage
Dockerfile - this dev environment has no Docker - so treat the first real
build as the thing to double-check, even though it mirrors exactly the
`npm run build` commands already confirmed working locally for both
projects. Same caveat for the self-hosted ffmpeg burn-in pipeline (see
docs/architecture.md): no ffmpeg binary is reachable here, so while its
pure logic (stream-index conversion, session lifecycle) is unit-tested
with `child_process.spawn` mocked, the actual command against a real
PGS file has never run in this environment. Treat the first real
attempt at a Blu-ray-style subtitle as the thing to double-check here.
**Resolved**: three Emby-API assumptions that used to be listed here as
unconfirmed (the ffmpeg direct-stream URL, the Playlists endpoint, the
Emby-playstate sync endpoint) were all checked directly against Emby's
own real OpenAPI spec. Two matched exactly. The third - playstate sync
- took three rounds: two request-shape bugs against Emby's
`PlayingItems/Progress` check-in endpoint (a missing `MediaSourceId`,
then a missing `PlaySessionId`), then a further report ("still don't
see this in my Emby profile") that questioned the whole approach - a
bare `Progress` report with no matching "Start" call may just never
reach the resume-position/watched-history data real clients read,
regardless of request shape. Switched entirely to a plain
`POST /Users/{userId}/Items/{itemId}/UserData` instead - confirmed
directly against the real server that this is exactly the data model
"Continue Watching" and the watched checkmark read, updated with no
playback session required at all - and added marking an item Played
(the other half of the same report) when the party moves past it.
Not yet confirmed end to end against a real server (no safe way to
fire a real, state-mutating test call without one) - see
docs/architecture.md's "Sync watch-party progress back to Emby"
section for the full story. The one-shared-stream-per-party work is a
different kind of unverified: its own Emby API calls were already live,
confirmed code, just newly shared instead of per-viewer - what's untested is behavior
under real multi-viewer load (whether a dead Emby session actually
surfaces as an HTTP failure the way the cache-invalidation logic
assumes, how a real transcode's seek handling feels once several
viewers depend on the exact same one).

Casting to a Chromecast (see docs/architecture.md) is the newest,
least-verified piece: the security-critical parts were checked against
the real running server directly (the party-stream/burn routes reject a
request with no auth exactly as before, and now also reject an invalid
`castToken`, both a plain 401) and the Cast SDK itself was confirmed to
load and initialize in a real browser, but there's neither a real
Chromecast nor Emby login credentials in this environment to take it
any further - the actual on-TV playback and the cast button's own
live behavior are unconfirmed.

## Project layout

Both `server/` and `client/` are TypeScript now (see
[docs/architecture.md](docs/architecture.md#typescript-and-a-service-oriented-architecture)
for the why and the migration itself) - each its own project with its own
`package.json`/`tsconfig.json`/build step; `server/src` and `client/src`
are the only source of truth, `server/dist`/`client/dist` are generated
(gitignored) and never hand-edited.

```
server/           Node.js + Express + Socket.IO backend: proxies ALL Emby
                  access (auth, catalog, images, HLS streaming) and
                  coordinates party/room state + realtime sync. The
                  browser only ever talks to this. TypeScript, compiled by
                  tsc to server/dist.
  src/index.ts                    Express app + route wiring only - thin,
                                   delegates to the services below
  src/config.ts                   env-derived config (EMBY_SERVER_URL, PORT)
  src/types.ts                    shared interfaces (Party, ItemDto, the
                                   Socket.IO event maps, ...)
  src/Logger.ts                   party/stream lifecycle logging
  src/emby/EmbyClient.ts          low-level Emby HTTP + response proxying (incl. HLS)
  src/services/AuthService.ts     server-side login + session store
  src/services/CatalogService.ts  all Emby browsing/streaming + DTO shaping
  src/services/PartyService.ts    in-memory party lifecycle (video queue, host handoff)
  src/services/MusicQueueService.ts  participative music queue - see docs/architecture.md
  src/realtime/SocketGateway.ts   Socket.IO protocol (see comments in the file)

client/           Frontend: TypeScript, esbuild-bundled to client/dist
                  (one app.js + one app.css - see client/build.mjs).
                  Talks only to server/ - never to Emby directly. Each
                  view is its own folder colocating its .ts/.html/.css.
  src/app.ts                 entry point - registers routes, boots the app
  src/router.ts              tiny hash router (unchanged in spirit - see docs)
  src/types.ts                shared interfaces (client-side copies of the
                               server's DTO shapes - see docs/architecture.md)
  src/api/embyApi.ts          calls our own /api/catalog/* + auth routes
  src/api/party.ts            our own backend's party REST + Socket.IO client
  src/tiles.ts + tiles.css    poster-tile rendering shared by home/library/artist
  src/styles/                 base.css (global reset/vars/primitives) +
                               small shared component styles (presence,
                               detail header, track list)
  src/shell/Shell.*            persistent sidebar + #mainContent the router swaps
  src/musicBar/MusicBar.*      persistent bottom-bar listen party - NOT a route,
                                mounted once by Shell.ts so it survives navigation
                                (see docs/architecture.md's "Music bar" section)
  src/views/login/Login.*      sign-in form
  src/views/home/Home.*        live parties carousel + per-library "recently added"
  src/views/library/Library.*  one library's tile grid (or artist grid, for music)
  src/views/series/Series.*    Series detail + season tabs + episode list
  src/views/artist/Artist.*    one artist's albums
  src/views/album/Album.*      one album's tracks - each track starts or queues
                                onto the active listen party (see musicBar/ above)
  src/views/player/Player.*    the /party/:id route's dispatcher (video takeover,
                                or hands off to musicBar/ + bounces back for music)

src/WatchParty/   The earlier Emby-plugin attempt (C#, unrelated to the
                  TypeScript above). Builds fine and installs, but Emby
                  has no supported extension point for a player button,
                  and even menu integration required reverse-engineering
                  undocumented internals - see docs/architecture.md for
                  the full story. Kept for reference; not the active
                  direction.

docs/architecture.md   full design doc for the standalone app
```

## Running locally

Both projects need `npm install` once; the server needs the client
already built at least once (it serves `client/dist` as static files).

```bash
cd client && npm install && npm run build && cd ..
cd server && npm install && npm run build
EMBY_SERVER_URL=https://your-emby-server npm start
```

Then open `http://localhost:3000`.

For active development, `client`'s `npm run watch` rebuilds on save, and
`server`'s `npm run dev` runs the server straight from TypeScript via
`tsx` (no separate compile step needed while iterating) - run both in
separate terminals.

Server tests (`server/test/*.test.ts`, Node's built-in test runner, no
extra dependencies or compile step):

```bash
cd server && npm test
```

`server`'s `npm run typecheck` also covers `server/test/`, not just `src/`
(see `tsconfig.test.json`).

## Deploying

Build the Docker image from the **repo root** (it needs both `server/` and
`client/`) - the Dockerfile compiles both TypeScript projects itself in a
build stage, so nothing needs building beforehand:

```bash
docker build -f server/Dockerfile -t watchparty .
docker run -d --name watchparty -p 3000:3000 -e EMBY_SERVER_URL=https://theater.media.kyuno.fr watchparty
```

Then put it behind your existing reverse proxy like everything else
(`theater.media.kyuno.fr`, `git.dev.kyuno.fr`, ...), e.g.
`watchparty.kyuno.fr` → `http://<container>:3000`.

## Roadmap

- [x] Design + scaffold the standalone app
- [x] Proxy all Emby access server-side; Emby-themed UI (sidebar, carousels)
- [x] TV show navigation (Series → Seasons → Episodes) + episode auto-queue
- [x] Player language/subtitle/quality pickers (all three are now
      host-only, party-wide choices — see docs/architecture.md's "One
      shared Emby stream per party" and "Text subtitles join burn-in as
      a party-wide, host-only pick")
- [x] Socket.IO instead of raw WebSockets; fixed two real memory leaks
      (dead-connection cleanup server-side, view teardown on navigation
      client-side) — see docs/architecture.md
- [x] Live "watch parties en cours" list (host, elapsed time, member count),
      live host handoff, no join codes
- [x] Presence overlay (avatars) + a request toolbar (pause/resume) in the
      player — see docs/architecture.md
- [x] Device detection: reconnecting from the same device is silent, a
      genuinely different device asks to confirm before disconnecting the
      other one — see docs/architecture.md
- [x] Server-side logging of the party lifecycle (create/join/leave/destroy,
      host handoff, play/pause, pause requests) — see docs/architecture.md
- [x] Music: dedicated player, Artist/Album/Track browsing, participative
      queue (free add, vote-to-skip, no host) — see docs/architecture.md
- [x] Full TypeScript rewrite (client + server), component-style client
      views (.ts/.html/.css each), server-side singleton services per
      feature — see docs/architecture.md
- [x] Automated server test suite (`node:test`) + CI job gating the Docker
      publish on typecheck+test+build passing — see docs/architecture.md
- [x] Music player as a persistent bottom bar instead of a page — browse
      and queue tracks while listening; starting a video party always
      leaves the listen party first — see docs/architecture.md
- [x] Self-hosted ffmpeg burn-in for PGS/image subtitles (Emby's own
      transcode can't render these as text) — one shared stream per
      party, host-driven — see docs/architecture.md
- [x] Browse Emby playlists and launch one as a pre-queued party (video
      queue or the participative music queue) — see docs/architecture.md
- [x] Sync watch-party progress back to Emby's own PlaystateService, per
      member's own account, including marking an item watched once the
      party moves past it — see docs/architecture.md
- [x] One shared Emby stream per party instead of one per viewer — see
      docs/architecture.md
- [x] Text subtitle choice joins burn-in as a host-only, party-wide pick
      (was still each viewer's own local choice until now); fixed the
      audio picker briefly showing an empty option on first load — see
      docs/architecture.md
- [x] Fixed catalog browsing feeling slow: image thumbnails were never
      cacheable (Emby's own Cache-Control/ETag were silently dropped) —
      see docs/architecture.md
- [x] Cast a party's video to a Chromecast (Default Media Receiver),
      with a play/pause/seek remote on the sender's own screen — see
      docs/architecture.md
- [ ] Try a full party end-to-end with two real accounts (still the main gap)
- [ ] Try casting to a real Chromecast (only the SDK's own bootstrap is
      confirmed here — no real device/session)
- [ ] Tune transcoding target / support direct play when possible

No chat, no OIDC — deliberately out of scope (Emby-only auth was the
explicit choice; see docs/architecture.md).

## License

MIT — see [LICENSE](LICENSE).