121 lines
6.4 KiB
Markdown
121 lines
6.4 KiB
Markdown
# How it works
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A five-minute tour. Details: [ARCHITECTURE.md](ARCHITECTURE.md), wire format:
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[PROTOCOL.md](PROTOCOL.md).
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## The pieces
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```
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your PC friend's PC
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+-------------------+ +-------------------+
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| app (mpv inside) | | app (mpv inside) |
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+---------+---------+ +---------+---------+
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| sync (WebSocket) | sync (WebSocket)
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v v
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+----------------------------------------+
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| server (who is ready, where are we) |
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+----------------------------------------+
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video bytes come from somewhere else:
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- a link (any http/https URL): the member who put it up passes it on
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through the relay (or each app, or the server, fetches it)
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- a Jellyfin item: each app plays it with its own Jellyfin account,
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friends without one through the server
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- a file on the host's disk: the server streams it (/m/... endpoint)
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- the relay (/r/...): a member's computer passes a file, a link or a
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Jellyfin item on to the server, which keeps a few minutes in memory
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and streams it to everyone who needs it
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```
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- **App**: the desktop window. It draws the video with mpv, shows who is
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here, and sends what you do (ready, seek, chat).
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- **Server**: keeps one shared clock and the list of people. It never sees
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video frames, only "position 123 s, playing". There is exactly one server
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and one watch session on it.
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- **Jellyfin** (or any web host): where the video lives. For a Jellyfin
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item the server only knows which item it is; each app signs in with its
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own account and reports what it watched. For friends without an account
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the member who put it up passes it on through the server (their sign-in
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stays on their computer).
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## Ways to run
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- **Your server**: every app runs its own server, quietly, from start to
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close, reachable only from that computer. You are on it when you are
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not in a friend's, so watching alone works like a session (progress,
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next episode). Invite opens it to friends on your network (a second
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listener on the same server: nothing restarts, the video and Up next
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carry on) and copies an invite link (`starsync://`, with your internet
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address when the app finds it and the password when one is set); Stop
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sharing closes it again. A friend clicks the link, or just copies it,
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and their app asks to join.
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- **Dedicated server**: `starsync-server`, a separate program in the
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release tarball, for an always-on box. See the README.
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Friends join either way with Join a friend in the strip at the top of the
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window; guests need no Jellyfin or account. Before connecting, the app
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checks the server's version and says who has to update when they do not
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match. Joining a friend leaves your server (it stays up); leaving theirs
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brings you back.
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## One session, start to finish
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1. **Connect.** The app opens a WebSocket to the server and says hello
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(version, password, name, avatar). Wrong password or version: refused with
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a reason. Otherwise the server answers with a welcome and the current state.
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2. **Catch up.** The app opens the current video, jumps to where the server
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says we are, and buffers. Arriving while the video is stopped, you are
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waited for; arriving while it plays, you never hold anyone back.
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3. **Ready gate.** Press Space to say you are ready. The server starts
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playback only when everyone who is ready has at least 4 seconds buffered
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(or what is left, near the end). At the end everyone stops and the server
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stays finished until someone seeks back or changes the video.
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Everyone who was there before it started must be ready, so one person
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alone cannot start it for the others. A lone viewer can play alone.
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4. **Play.** The server owns the clock. Each app compares its mpv position
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to the clock: a small lead slows mpv a little (0.95x), a big gap (over 5 s)
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jumps. If someone's buffer runs dry the server pauses everyone and resumes
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when they have caught up.
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5. **Seek.** Anyone can seek, anytime. The server moves the clock and
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everybody follows. Seeking does not change anyone's ready flag.
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6. **Swap.** Anyone can change the video by pasting another link. Everybody
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stops at 0 and the gate runs again for everyone there; ready flags stay
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as they were (a setting unreadies you instead).
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7. **What's next.** Up next is one list on the server for everyone, and
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an episode you put up is followed by its next one. When a video ends
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with something next, the server counts down 10 s on every screen;
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anyone can cancel it for everyone (a seek stops it too). At zero the
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app that has what plays next puts it up; if that person is away for a
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moment, the countdown waits for them.
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8. **Leave.** Closing the app or Leave says goodbye and drops you from the
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server; the others keep going. If you vanish without a goodbye, after 15 s
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of silence you are "gone": you stop blocking but keep your place
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(ready flag, sitting out, Up next items, the video you pass on) for
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10 minutes. The app keeps playing and reconnects by itself, with an id
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of its own, and takes that place back.
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There are no roles: anyone can seek, swap, force-ready others, nudge
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anyone, and sit anyone out (the host too). Someone sitting out stays
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connected and in the chat, but their app loads nothing and nobody waits
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for them until they join back.
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Watched or not is counted by the time you were there while it played:
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sitting out, skipping around or a quick look never counts as watching.
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Jellyfin hears it for your account; files and links are remembered on
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your computer.
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## Where video comes from
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- **Link**: you paste an http(s) URL. By default your computer opens it and
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passes it on (it plays for everyone whenever it plays for you, cookies
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included); under "Other ways" every app plays it directly, or the server
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fetches it once. A web page (YouTube, X, ...) goes through yt-dlp, which
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the app and the server download and update by themselves.
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A pasted Jellyfin link becomes the Jellyfin item below when possible.
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- **Jellyfin item**: picked in the app's library browser. Shared as "this
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item on this Jellyfin server", never as a link with someone's sign-in.
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- **Local file (host only)**: you pick a file on your disk. The server
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streams it to everyone, host included, over HTTP with range requests, each
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with a per-person token. Nothing is stored or converted.
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- No transcoding, ever. Quality is whatever the file is.
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