simulcast-mpv

A way to sync multiple mpv players over the internet.

• If someone pauses/resumes, then pause/resume for everyone.
• If someone seeks forwards/backwards, then seek for everyone.
• Add in some ping calculation between clients.

That's basically what simulcast-mpv is.

Usage

TL;DR:

• Download simulcast-mpv
• Run simulcast-mpv. It will install itself.
• Start mpv. It should just work™.
• (optional) Hit a once to show some info. Hit a a few times really fast to open up an input window for custom room codes. (Maybe you and your friend are watching the same thing, but your file names are different.)

The simulcast-mpv executable has 4 "modes":

• simulcast-mpv
  • This "installs" simulcast-mpv to your mpv scripts directory (%APPDATA%\mpv\scripts or ~/.config/mpv/scripts). It also writes a helper lua script (simulcast-mpv.lua) to the directory.
• simulcast-mpv client
  • This is ran when mpv starts. It acts as a middle-man for sending pause/resume/seek messages between mpv and the relay server.
• simulcast-mpv relay
  • A websocket server
• simulcast-mpv input-reader
  • A popup command prompt window for inputting custom room codes.

TODO:

• Log simulcast-mpv things to mpv console.
• setup github actions to compile binaries for 64-bit ARM Linux (and also publish binaries to a release tag...).
  • cargo +1.75 build --release (1.75 for Windows 7 support)
  • cargo zigbuild --release --target x86_64-unknown-linux-musl
  • cargo-dist? I don't particularly want to package .msi installers though...
• Fix some logic bug that gets you trapped in a pause/unpause loop.

similar projects (for mpv)

• Syncplay: website / github
  • More feature-complete than simulcast-mpv.
• https://github.com/po5/groupwatch_sync
  • Manual groupwatch project.
• others? dunno...

similar projects (not for mpv)

• Jellyfin has some "SyncPlay" thing.
• Plex (ew) has a "Watch Together" thing.
• Metastream does streaming & syncing on a webpage.

Environment variables / .env

simulcast-mpv allows environment variables and files to configure some of the settings.

client

• SIMULCAST_RELAY_URL / --relay-url (default: reads the server from here)
• SIMULCAST_RELAY_ROOM / --relay-room (default abcd1234)
• SIMULCAST_CLIENT_SOCK / --client-sock (passed by mpv to the simulcast-mpv executable)

relay server

• SIMULCAST_BIND_ADDRESS / --bind-address (default 127.0.0.1)
• SIMULCAST_BIND_PORT / --bind-port (default 30777)
• SIMULCAST_REPO_URL / --repo-url (for AGPL-3.0 reasons. Set this in your .env file if using 'docker compose')

Configuration files can be placed at

• %APPDATA%\mpv\scripts\simulcast-mpv.env (Windows)
• ~/.config/mpv/scripts/simulcast-mpv.env (Unix)
• $PWD/simulcast-mpv.env (current directory AKA where mpv is started from) (Windows + Unix)

Running the server (the intended way)

git clone https://github.com/rtldg/simulcast-mpv.git
cd simulcast-mpv
echo "SIMULCAST_REPO_URL=https://github.com/rtldg/simulcast-mpv" > .env
docker compose up -d

## then install caddy and reverse-proxy to 127.0.0.1:30777 like in this Caddyfile:
##  mydomain.com {
##    handle /simulcast-mpv {
##      reverse_proxy 127.0.0.1:30777
##    }
##  }

# To update:
git pull # update latest repo changes
docker compose build --no-cache simulcast-mpv-relay # rebuild or something lol... not sure if --no-cache is needed
docker compose down
docker compose up -d

Relay server privacy

Relay server "rooms" are public to anyone who joins using the same "room ID".

"Room IDs" are calculated client-side as blake3_hash(filename + relay_room) where relay_room is configurable with SIMULCAST_RELAY_ROOM/--relay-room.

This means the server cannot know which file you are playing unless the server already knows what the filename + relay_room combination is.