Starsync

Watch a video with friends, in sync, with the quality of a real mpv player. Pick from your Jellyfin library, paste any direct video link, or pick a file on your own disk; everyone's play, pause and seek stay together.

Why not Jellyfin SyncPlay: it runs in the browser and its sync is poor. This is a desktop app that drives mpv.

Up to 1.2.x the app was called watch_together (its files watch-together-*); the repository and the update manifest keep their old addresses for now.

• Desktop only (Linux and Windows), always mpv. No web clients.
• No transcoding. Everyone plays the original file.
• Friends trust model: no accounts, no roles. A blank password means an open server.

How it fits together: docs/HOW-IT-WORKS.md.

Install and update

From the Releases page of this repo:

• Linux: starsync-<version>-linux-x64.tar.gz. Extract, run starsync. On start it adds itself to your app launcher (and its icon), so the window shows its own icon on Wayland. Needs mpv's library installed (mpv or libmpv2).
• Windows: starsync-<version>-windows-x64.zip. Extract, run starsync.exe. mpv is bundled. New and not yet tried on a real Windows desktop; reports welcome.

The folder also holds watch_together(.exe) and watch-together-server(.exe), the names up to 1.2.x: they start the new programs, so an update from 1.2.x restarts fine and old shortcuts and service files keep working.

Your data (settings, sign-ins, folders, logs, yt-dlp and its cookies) lives in ~/.local/share/dev.foxyz.starsync on Linux and %APPDATA%\foxyz\Starsync on Windows. The first start after 1.2.x copies it over from the old places (~/.local/share/moe.senkochan.watch_together or %APPDATA%\com.example\watch_together, and the app's files in your Documents folder) and leaves the originals where they were.

Update from the app: the app looks for a new version at start and every few hours, and when one exists a band across the top of the window says so (never over a playing video). "Update and restart" downloads, verifies, applies in place and restarts; "Later" hides it until the next check; the install folder must be writable by you. The version you run is at the bottom of every Settings page (and in the Settings tab's tooltip). Settings has Check now and an auto-check toggle. From a terminal: ./starsync-server --upgrade (no display needed, so it works on a server box too), ./starsync --upgrade, or the shipped update.sh / update.bat (which run the first). Each updates the whole folder, app and server; restart whichever is running to use the new version. A release with a newer protocol is a required update: everyone on a server must run the same protocol version, and a mismatch is refused with a message telling you to update.

Getting started

The app always runs its own server, quietly: your server. When it starts you are on it, alone, and it is a plain player. Three ways in, at the top of the Library the first time; none needs Jellyfin or an account.

• Join a friend (most people): your friend sends you an invite (an address) and, maybe, a password. See Join.
• Invite friends: you have the video and friends watch it with you. See Your server and Invite.
• Watch on your own: just play something from the Library, with everything a server has (Jellyfin progress, next episode, skip buttons). Nobody else can reach your server until you invite them; inviting never interrupts what plays.

The window

One window. Along the top, the strip: your avatar (click it for your profile: name, picture with a crop editor, colour, and links to the settings), the Library / Schedule / Settings tabs, and the party. Alone on your server it has just Join a friend and Invite (and "Sharing" while your server is open to friends); with others there it shows everyone's avatar with a ring for their state (green ready, amber buffering, grey not ready, a little faded joining, dimmed reconnecting, dimmed with a moon sitting out; a crown on whoever hosts, a tower on whoever passes the video on). Click the avatars for the member list (each member's app version, amber when it differs from yours, and the server's at the top; force ready, Nudge, Sit out; on your server the invite with Copy invite and Stop sharing, on a friend's "Copy invite address"). Beside them the server and "ready n/m" (who is sitting out or reconnecting does not count), the chat button with unread count, and Invite on your server or Leave on a friend's. Empty strip space drags the window.

The player fills the window under the strip. Pick a tab and it shrinks to a mini player in a corner: drag it anywhere and it snaps to the nearest corner; double-click or ⤢ makes it big again, × sits you out (below) and × again closes it; the strip's screen button brings it back. F or double-click on the picture goes fullscreen (the strip hides, the party shows in a corner while paused, the window buttons sit in the player's top bar while its controls are up), Esc leaves it. The controls show the show's cover, title and episode top left (a web video: its thumbnail and name; guests get the art too; right-click to copy the title, or the link when you have it, or open it in the browser or Jellyfin); before a video first plays, its banner fills the picture until playback starts. One pill bottom centre, just above the controls, says what playback waits for ("Press Space when you're ready", "Waiting for Bob and Mika · 2/3 ready", "Bob is loading…") or what went wrong, with Retry or Cancel when it helps. Chat and activity open in a panel on the right (chat button or Tab), ready to type; it shows messages (select text to copy it, or right-click for Copy message and, with a link in it, Copy link / Open in browser), and its "Activity" toggle adds joins, ready, seeks and the like between them. Joins, leaves, someone losing connection and coming back, video changes, additions to Up next (the title, its picture and who added it), chat and problems also pop up bottom left with the person's avatar, above the player's controls (never on them); ready, seeks and pauses stay in the activity. Click a message to open the chat (Settings → Notifications & sounds → Chat messages: All by default, or Only when paused, or Off; messages always reach the chat, with their sound). Watching alone, nothing pops up or sounds about the party (there is nobody); the app's own notices still show.

While sitting out or in the background. Sitting out, only chat, nudges, "starting now" (the video starts for the others) and Up next reach you; joins and leaves too if you turn on Settings → Notifications & sounds → "Joins and leaves too". With the window in the background or minimised, the same ones also come as desktop notifications (Linux's notification center, Windows' toasts); clicking one brings the window up, and a chat one opens the chat. Unread chat shows as a count on the chat buttons and, in fullscreen with the controls hidden and the video paused, as a small chip top right.

Your name and picture change for everyone in the server right away; the colour is yours only.

Sitting out. Step away without leaving: Sit out (your profile, your row in the member list, or × on the mini player) unloads the video on your end, and nobody waits for you any more; you stay in chat. Anyone can sit anyone out, the host too ("Alice sat you out" tells you who). The player then shows the cover, title and where the others are; Join back (or Space) loads the video there and readies you, in the background while the others play on (nobody is paused for you).

Auto sit-out. Idle for 5 minutes while nothing plays, or the window minimised for 10 minutes (playing or not), sits you out by itself, so nobody waits for you; you are back as soon as you return (a key, the mouse, the window's focus). It never happens when you are alone, and an away you chose (or someone else's) stays until you join back. Settings → Party & network → "Auto sit-out" turns it off.

Reconnects. A bad connection does not throw you out: the video keeps playing, the pill says "Connection unstable…" and then "Reconnecting…", and the app comes back on its own as the same member (ready, sitting out, your Up next items and the video you pass on all kept) for up to 10 minutes; the others see you dimmed, "reconnecting…". Only a drop of a few seconds or more makes the lost / back sounds. Leave and closing the app tell the others at once; Update and restart keeps your place for the restarted app. Opening Starsync a second time (another window with the same profile) takes your place over, and the first one says so and stops.

Nudge. Nudge in the member list pokes someone, sitting out or not: only they hear it (a sound, a pop-up, and the taskbar entry asks for attention when the window is in the background).

Your server and Invite

Your server starts with the app and stops when it closes. Only this app can reach it until you press Invite (in the strip, or in the member list): that opens it on your network at the port from Settings → Party & network (default 8080, with the password set there; blank = anyone can join) and copies an invite ("Join me on Starsync: 192.168.1.20:8080 · Starsync 1.3.0") to send to friends. Nothing restarts: what plays and Up next carry on, and you are the host (the crown). The invite picks this computer's home-network address (not a VPN or proxy one, nor a Docker or VM bridge). Friends elsewhere need the TCP port forwarded on your router (or a VPN address, or a server they can all reach, like a VPS). Friends open nothing. Stop sharing (in the member list) closes it again: everyone else leaves (their app goes back to their own server and says why), you and Up next stay.

If you put up a local file, your server streams it to everyone from your disk. Nothing is uploaded or stored anywhere.

Joining a friend leaves your server for theirs; it stays up meanwhile, and leaving theirs brings you back to it as you left it.

Library

What to watch, from three sources (the switch at the top). Drop a video, a folder or a link anywhere on the window, or press Ctrl+V outside a text field, and a small card asks how to open it (put it up, add it to Up next, add the folder to Files, or fill Link).

• Jellyfin: your linked servers (see below); with none linked it points to Files and Link and offers Jellyfin as optional. Library chips beside the switch, then one Continue row (what you were watching and what comes next, one card per series, the one you watched most recently first; series not touched for two months drop out) and Latest in each library (one card per series: "S1E1" or "3 new"; Show all opens the library newest first). Re-uploads (added long after they aired) are hidden from Latest; the row's ⋮ menu turns that off. Search (/), library grids (sort, unwatched, favourites) and series pages sit behind them. Click a card to select it: its details open on the right with "Put it up · S1E3", mark watched / unwatched, remove from Continue and the episode list (click an episode to choose it). Double-click a card or an episode to put it up at once. Right-click a card or an episode to copy its title or open it in Jellyfin's web page (the details panel has that button too).
• Link: paste an http(s) link: a video file, or a web page with a video (YouTube, X, and whatever else yt-dlp knows). The preview shows what it is (a page's title, uploader, length and thumbnail, else the file name); in a server, pick how the others get it (everyone fetches it, the server fetches it, or through you). Your last 12 links are listed under it (right-click one to copy or open it). A link seen before shows its preview at once, without asking the site again. A link that does not open here (needs cookies, 403, 404, not a video) says why and goes up only with "Put it up anyway"; in the player, whoever cannot play it is named ("Bob can't play this: Not allowed (403)") and nobody waits for them.
• Files: your own library from the video folders you add on this computer (the Library shows them all together, each folder on its own too), or any file through Browse. Files are sorted into shows and movies by their names and folders: one show split over several folders is one show, OP/ED and specials go under its Extras, a folder like "Show (Season 3 - Alicization)" gives the season and its name. Shows are looked up on AniList for their proper name, cover and banner. A show's page has its seasons and episodes and a button for the next one after what you last watched here; when episodes are missing on the way it says so ("66–107 aren't in your folders — skip to 108?"). An episode you put up continues with the next one at its end (see Up next). Matched the wrong show? Wrong show? searches AniList and pins the right one for the show everywhere or just one folder; Episode numbers… says which episode the first file is when the files count differently. Both stay through rescans. The others stream what you put up from you, and see its proper name too.

Put it up and the player opens. With nobody else in the server, the buttons say Play and a link plays straight from the site.

Up next (the queue)

Anything can wait its turn instead of going up now: Add to queue on the Link page (in the way you picked), or right-click a Jellyfin card or episode, a video in Files, a recent link or an episode on the Schedule for Add to queue / Play next; the Jellyfin details panel has a queue button (right-click it to play next), and the card for a dropped or pasted video or link has both. A link is checked first, like Put it up. Every app keeps the next item ready, its first seconds already loaded, so skipping to it starts at once. For a link passed on, a member's file or a link the server fetches, the server starts getting the next item while the current one plays (from the app of whoever added it, or by fetching the link itself), so everyone has its start before it goes up; whoever added it keeps the app open for that. Everyone shares one Up next and anyone can change it; what you added stays when you leave.

In the player, Up next sits in the top bar, right of the title: the next item's picture and title (or what continues the episode). Rest the mouse on it for a larger preview (who added it, its length, whether it is ready to start); ⏭ plays it now, a click opens the queue: drag rows to reorder, hover a row to play it now (▶) or remove it (×), right-click it for more (copy its title or link, open it in the browser or in Jellyfin). To add, press Ctrl+V with the queue open (a copied link or video file goes in at once, its title and picture showing while it is checked), type one after + Add link, or drop a link or a video on it. When a video ends, a card shows what is up next with a 10 s countdown everyone sees, and it plays; Cancel stops it for everyone, and so does seeking back. > or Shift+N plays it at once. Under the queue, Continues with shows what continues the episode playing: its next episode (a Jellyfin episode's, or a file's next one in your Files library, saying which numbers it skips), added by whoever put the episode up, and greyed because it plays only once Up next is empty; Clear drops it for everyone. The further episodes of a Jellyfin series show under it; + adds one.

A link you pass on ("through me") or a file of yours can only be played by your app: if you left when its turn comes, it is skipped ("Skipped …: Foxyz left"). If you are only gone for a moment, the countdown waits for you. A Jellyfin item needs someone with an account on that server. Up next is kept by the server while it runs. If the server restarts, the apps put back what was playing, where it was, and Up next with it (a link the server fetched has to be added again).

Schedule

The week's airing anime, one column per day (AniList), each episode marked with what the Jellyfin server has of it when AnimeFlow is connected (Settings, Jellyfin & integrations): on Jellyfin (Put it up, right-click to queue), downloading, waiting for release (aired in Japan, AnimeFlow downloads it by itself once a release appears; with when AnimeFlow last searched, or release rejected when it found releases it won't take, the reason on hover), failed, not monitored (Request asks AnimeFlow for it), or the time left until it airs. A show AnimeFlow does not follow can be asked for with Request series. Episodes you already watched on Jellyfin carry a check on the cover; one you started shows how far you got.

Dedicated server

For an always-on box (no display needed): the release tarball also contains starsync-server, a small standalone server without the app. Run it, then everyone (you included) uses Join.

./starsync-server --port 8080 --secret <password>

Flag	Default	Meaning
--port, -p	8080	TCP port, all IPv4 interfaces
--secret	empty	password; empty = open server (a warning is printed)
--name	server	name reported by /health
--media	none	local file to serve as the starting video
--advertise-host	none	host put in file URLs instead of the one each viewer dialled
--[no-]yt-dlp	on	read web pages (YouTube, X, …) with yt-dlp when the server fetches a link
--yt-dlp-dir	next to the binary	writable folder for the server's yt-dlp (systemd: the unit's StateDirectory)
--yt-dlp-cookies	none	cookies.txt or cookie-extension JSON export for that yt-dlp (sites that refuse guests); copied into the yt-dlp folder at start, removed from it when not given. An account login: keep it private, use a throwaway account for YouTube
--log-dir	logs next to --config, else next to the binary (systemd: the unit's StateDirectory)	folder for the log files (server-YYYY-MM-DD.log and the session log session-YYYY-MM-DD.log, kept 7 days; passwords, tokens and cookies left out)
--config	none	YAML or JSON file with the same settings (port, secret, name, mediaPath, advertiseHost, ytDlp, ytDlpDir, ytDlpCookies); replaces the flags
--upgrade		update the install folder to the latest release (Install and update), then exit
--check-update		print whether a newer release exists, then exit

It prints READY port=... name=... once listening and stops cleanly on Ctrl+C or SIGTERM. A dedicated server has no host. To run it as a service, unpack the tarball to /opt/starsync and use deploy/starsync.service (copy it to /etc/systemd/system/, edit the flags, systemctl enable --now starsync). A service set up before the rename (/opt/watch-together, running watch-together-server) keeps working as it is.

Something not playing? Settings → About → Copy diagnostics puts the app's recent log (passwords, tokens and cookies left out) on the clipboard: paste it to whoever helps you, from both sides if you can.

While you are in a server, the app also sends its log to that server, which merges everyone's lines and its own into one session log (session-YYYY-MM-DD.log next to the server's logs; your own server keeps it in the app's logs folder), so a problem can be read afterwards from every side. Chat is never logged anywhere, nor passwords, tokens and cookies. When something goes wrong, press Mark a problem (Ctrl+Shift+B, also in the player's ⚙ and Settings → About) and add a few words if you like: a marker with your name goes in the session log at that moment. In a server, Copy diagnostics can add the session log of the last 6 hours (any member may read it). Don't want to share? Settings → About → Share diagnostics with the server off: your log stays on your machine (the server only notes that you don't share; a problem you mark still goes in).

Join

Join a friend in the strip. Servers you got into are listed first (up to 6), with live status (online and how many are watching, or offline, plus "needs update" when its version and yours do not match): click one to rejoin, x to forget it. Or paste the invite (or the address and port) and the password if there is one, then Enter or Join. Before connecting the app checks the server's version: when they do not match it says who has to update ("Bob's server runs Starsync 1.2.1 — they need to update"), and offers the update when it is you. Your name and picture come from your profile (your avatar at the top left). Leave goes back to your own server.

Settings

The Settings tab (Ctrl+,) has a page per topic, each setting with a line of help: Profile; Party & network (your server's port and password for Invite, recent servers with remove); Player (below); Jellyfin & integrations (linked Jellyfin servers, below, the AnimeFlow connection: "connected as " with what you may do, or why not, and playing the next episode automatically); Notifications & sounds (what pops up, chat pop-ups, what reaches you while sitting out or in the background; the sound volume and sound set, and every sound with a preview, its own set and a switch); Updates; Keyboard shortcuts (read-only); About (the version, also at the bottom of every Settings page and in the Settings tab's tooltip; and the credits, e.g. that the Minimal player design is inspired by uosc).

Player settings live in the player too: ⚙ → Player settings, at the right of its controls, and Settings → Player has the same ones (plus the controls' layout and the custom shader files). Player design: Standard or Minimal (below); progress line when hidden (on by default: a thin line at the bottom of the video while the controls are hidden); upscaling shader (see below); hardware decoding (auto, off or custom; auto is mpv's auto-copy on Windows, auto elsewhere; the env var SYNC_RELAY_HWDEC overrides it); in the player also the subtitle and audio track. Settings → Player → Controls: time display (elapsed / total or remaining), controls size (normal or large), hide the controls after 2, 3 or 5 s, and which optional buttons sit in the bar (chapter buttons, subtitles, audio, chat; hidden ones are still in ⚙). Every change applies right away.

Anywhere in a server (unless you are typing): Space = ready / unready, Tab = chat & activity (Tab never moves between buttons). Anywhere: Ctrl+Shift+B = mark a problem in the session log. Keys while the player fills the window: Left/Right = seek 10 s, Up/Down = volume, Shift+Right = skip 1:30, PgUp/PgDn = previous / next chapter (as in mpv), F = fullscreen, Esc = close the chat, then fullscreen, then shrink the player to mini; from the mini it asks to leave, Ctrl+R = reload video, < / > or Shift+P / Shift+N = previous / next Jellyfin episode, Ctrl+1..6 = Anime4K mode A, B, C, A+A, B+B, C+A, Ctrl+0 = shaders off. Every seek, skip and chapter jump moves everyone.

Controls: both designs have the same buttons in the same places, only the look differs. Bottom left: play / pause first (it is your ready, like Space: ✓ while you are ready and the others are not), previous / next episode (when there is one; next plays Up next first), previous / next chapter (when the video has chapters), volume and the time (click it to switch between elapsed / total and the time left). Bottom right: Subtitles and Audio (with the track count; tracks listed as "Japanese · E-AC3 2.0 · title", subtitles with Off), ⚙, chat and fullscreen last. Everything else is in ⚙: chapters (current one checked; click to jump), Skip 1:30, upscaling shader, change video, copy link, reload video, mark everyone ready, mark a problem, player settings and leave. The top bar has the title, Up next and back to the library (in fullscreen: exit fullscreen and the window buttons). Volume (scroll anywhere on the video, hover the speaker, or Up/Down) goes to 150 % like mpv: past the tick at 100 % the bar turns amber and mpv amplifies; a scroll or key shows the volume for a moment. Lists and menus under the mouse scroll as usual.

Standard (the default): a seek bar that marks chapter starts with a diamond (hovering it shows the time and the chapter title) over a row of round buttons. Minimal (⚙ → Player settings → Player design, switches right away): a translucent timeline across the bottom tints what has played, stripes the part not downloaded yet, marks chapter starts with dots (click one to jump), shows the elapsed time left and the total or the time left right (click it to switch) and, while less than a minute is buffered, the buffered seconds next to the position; hovering it shows the time there and the chapter title. With the controls hidden it stays as a thin line (unless "Progress line when hidden" is off). Its buttons sit in two glass capsules above it. Minimal's timeline and controls are inspired by uosc by tomasklaen (LGPL-2.1).

Skipping: during the opening a "Skip OP" button shows bottom right, just above the controls (it jumps to the end of the opening), during the ending "Skip ED" (to the end of the ending only; what comes after is yours to skip). "Skip OP" and "Skip 1:30" show for 5 seconds when they come up, then only while the controls are up (move the mouse); "Skip ED" and "Next episode" show only while the controls are up. The opening and ending come from Jellyfin's intro / outro segments when your Jellyfin has them (needs a segment plugin, e.g. Intro Skipper), else from chapter names (OP, Opening, Intro / ED, Ending, Credits, Outro). Without an opening or any chapters, on anything longer than 20 minutes, "Skip 1:30" floats there during the first 6 minutes.

Ports

What	Default	Notes
Sync WebSocket and /health	TCP 8080	plain ws://, no TLS
Local file streaming	same port	path /m/..., needs a session token

Only the one who invites needs the port reachable; until Invite your server listens on 127.0.0.1 and a free port only.

Jellyfin

Settings > Jellyfin & integrations > Add server: type the address, then sign in with Quick Connect (the app shows a code; approve it in Jellyfin under Profile > Quick Connect) or your username and password. Several servers can be linked; each shows its status, and a star picks the default. Sign out revokes the app's sign-in on the server. If a sign-in expires the server shows "Reconnect" instead of disappearing.

The Library's Jellyfin source is a library browser: Continue watching (with time left), Next up and the latest per library on the start page; library grids with sort (name, date added, release date, rating, random) and Unwatched / Favorites filters; series pages with seasons, episode progress and a "Next up" button; details with the file's tracks; search. Clicking a movie or episode picks it. On wide windows a side pane shows details of whatever is under the mouse.

Keys in the browser: arrows move, Enter picks or opens, I = details, Esc / Backspace / Alt+Left = back (Esc first clears a search), / or Ctrl+F = search.

Putting up a movie or episode sends only the item to the server (which Jellyfin server and which item), never a link or your sign-in. Pasting a Jellyfin link (web page or stream link) does the same when the app can reach that Jellyfin; otherwise it is shared as a plain link.

Watching:

• Everyone with their own account on that Jellyfin server plays the file directly with their own sign-in. Jellyfin tracks progress per account: your watched state, Continue watching and resume point follow what you saw (reported on start, every 10 s, on pause, resume, seek and track change, and when it stops). Watched means you were there while most of it played (or while half of it played and it reached the ending), not where it stopped: time you sat out does not count, skipping around does not count, opening a watched episode to check a moment keeps it watched, and a quick peek leaves no resume point. Files and links you watch are remembered the same way on your computer (a show's next episode in Files follows them).
• Friends without an account watch through the server: whoever put the item up passes it on automatically, with their own sign-in, which never leaves their computer (only the current item, only to people in the session). They show "via server" in the member list (click the avatars). On your own server (with your sign-in on that item's Jellyfin, whichever of your linked servers it is), or a dedicated server with its own login (--jellyfin <file>, see docs/ARCHITECTURE.md, Jellyfin relay), the server fetches it itself instead.
• If nobody can pass it on (the person who put it up left), the app says "No Jellyfin account here for ..." with a button to link one; it plays as soon as you are signed in.

Episodes: the ⏮ / ⏭ buttons next to play (or < / >, Shift+P / Shift+N) put up the previous or next episode for everyone. From the ending (when it is known, see Skipping above; else in the last two minutes) a "Next episode" button floats in the corner while the controls are up. With "Play the next episode automatically" (Settings, on by default), the episode you put up continues with the next one: when it ends, everyone sees a 10 s countdown, and anyone can cancel it (see Up next). Anyone with an account can put the next one up; friends watching via the host cannot.

Audio and subtitles: the Audio and Subtitles buttons in the controls pick tracks. Your choice is remembered per series (and as a default) and the closest match (language, then title, then codec and channels) is selected on the next episode. This is per person; nobody else is affected.

⚙ → Change video in the player opens the Library tab (the player goes mini): the library starts on the series you are watching with the current season, else where you left it.

Anyone can put up a file from their own computer, also on a dedicated server: it streams from your computer through the server to everyone (the server keeps a few minutes in memory, so seeks and skipping the opening are quick). Keep the app open while it plays. A link goes up "Through me": your computer opens it and passes it on, so it plays for everyone whenever it plays for you (you can't tell ahead which sites want cookies, and YouTube may start asking any day). Under "Other ways" there are two more:

• Everyone fetches it: each app plays the link itself.
• Server fetches it: the server downloads it once for everyone, for links that are slow or blocked for some. The server must be able to reach it, and it must have a password (an open server refuses: anyone could make it fetch addresses only it can reach).

Web pages work in all three: the app and the dedicated server each download yt-dlp by themselves (checked against the release's checksums, updated once a day; Settings → Player shows its version and has "Update now"), so there is nothing to install. Sites that refuse guests (Bilibili answers "HTTP Error 412", YouTube may ask to sign in) need cookies: Settings → Player → yt-dlp → Cookies reads them from a browser, or from a cookies.txt or a cookie extension's JSON export (picked or dropped; every site in it is kept). They stay on this computer and are used by its yt-dlp only (your own playback, "through me", and a server you host). Cookies log yt-dlp in as you on those sites: keep the file private, and for YouTube consider a throwaway account (Google may flag accounts used with yt-dlp). When a page shows no video, the message says which cookies were used: none, your file (and whether it has any for that site), or your browser's (and how many it has for that site), so you know whether to sign in there or add cookies. YouTube works in all three too, and so do pages and links that only offer streaming playlists (HLS .m3u8, DASH .mpd, the HLS of X videos). Through me and Server fetches it never show the link to anyone; they can't pass on live streams or DRM-protected video (use "Everyone fetches it" for live). Your upload has to beat the video's bitrate: a 25-minute 2 GB episode is about 11 Mbit/s.

The member list (click the avatars) shows where the video comes from on top: who passes it on, or that the server fetches it, everyone plays the link, or everyone streams it from Jellyfin, with how many watch through the server and, for a relay, how fast it arrives against what the video needs (the bar's mark; past it is keeping up). It turns amber when the source is too slow or its connection dropped ("Bob's connection dropped — playing what the server has (2 min)"), red when it left (the others play out what the server already has; the player's pill says the same and a pop-up tells you once), and whoever passes it on is told once when their upload is too slow. Each member's line says how they get it ("via server" with their speed, or "direct") after a dot for their buffer: green enough to play on, amber low, red empty. A red dot on one member while the source keeps up is their own connection.

Video quality and shaders

Each viewer can run mpv GLSL shaders on their own picture; nobody else is affected. The app ships Anime4K v4.0.1 (MIT) with the presets of its mpv guide: Mode A (1080p sources), B (720p), C (480p), A+A, B+B, C+A, each as HQ (strong GPUs, GTX 1080 and up) or Fast (the guide's low-end set). "Custom shaders" runs your own .glsl files.

Pick one with ⚙ → Upscaling shader in the player (also in fullscreen) or Ctrl+0..6; the change applies live and is saved, so the next session starts with it. ⚙ → Player settings and Settings → Player set it too, with HQ or Fast (used by Ctrl+1..6); Settings → Player holds the custom files. Shaders cost GPU time every frame and need hardware video rendering: on media_kit's software fallback they do nothing, and the app says so. A shader that is missing or fails to load shows a toast and switches shaders off.

Troubleshooting

• "host offline - check address and port": wrong address, or the port is not open.
• "wrong server password": password mismatch.
• "host runs a different version": update the app on both sides.
• Picture frozen but sound fine: Ctrl+R reloads the video.
• Everyone waits at "waiting for X": X has not buffered 4 seconds yet or has not pressed Space.
• Windows: the build is new; if something is off there, say so.

For contributors: docs/DEVELOPMENT.md, docs/ARCHITECTURE.md, docs/PROTOCOL.md.