84 lines
3.0 KiB
Markdown
84 lines
3.0 KiB
Markdown
|
# Sync play for MPV
|
||
|
|
|
||
|
|
Goal: write an Odin application to sync playback between remote viewers via a small Odin program.
|
||
|
|
|
||
|
|
The program will be called `syncplay`. The player is called `mpv`. `syncplay` is a single executable that can be run by clients, and is also executable in a remote server that functions as events dispatcher. The server is required.
|
||
|
|
|
||
|
|
Use case: two friends want to see the same movie using MPV, and they want synchronized playback. If one pauses, the video pauses for the other viewer. If one seeks to xx:xx:xx, also the other player seeks to xx:xx:xx.
|
||
|
|
|
||
|
|
**Server**
|
||
|
|
|
||
|
|
```sh
|
||
|
|
./syncplay server --port <port> --host 0.0.0.0
|
||
|
|
```
|
||
|
|
|
||
|
|
**Client**
|
||
|
|
|
||
|
|
```sh
|
||
|
|
./syncplay client --port <port> --host <remote-ip> \
|
||
|
|
[--mpv <mpv-path>] [--socket <socket-path>] <movie>
|
||
|
|
```
|
||
|
|
|
||
|
|
Supported operations:
|
||
|
|
|
||
|
|
- play
|
||
|
|
- pause
|
||
|
|
- seek
|
||
|
|
|
||
|
|
On macOS, the client launches MPV with a JSON IPC UNIX socket. `syncplay`
|
||
|
|
connects to that socket, observes pause changes and seek events, and sends JSON
|
||
|
|
commands to apply events received from the relay server.
|
||
|
|
|
||
|
|
The TCP protocol is newline-delimited JSON. There is one global session, no
|
||
|
|
authentication, and no server-held playback state. Messages are absolute state
|
||
|
|
changes:
|
||
|
|
|
||
|
|
```json
|
||
|
|
{"version":1,"type":"welcome","client_id":1}
|
||
|
|
{"version":1,"type":"pause","paused":true}
|
||
|
|
{"version":1,"type":"pause","paused":false}
|
||
|
|
{"version":1,"type":"seek","position":123.456}
|
||
|
|
```
|
||
|
|
|
||
|
|
The server assigns a numeric ID when a client connects and includes the
|
||
|
|
triggering ID in every relayed event. Both server and client terminals log each
|
||
|
|
play, pause, and seek action with that client ID.
|
||
|
|
|
||
|
|
Clients start paused at `00:00:00` and are assumed to use the same movie. There
|
||
|
|
is no clock synchronization or drift correction. If a connection is lost,
|
||
|
|
playback continues locally and the event is logged; clients do not reconnect.
|
||
|
|
|
||
|
|
**Example flow**:
|
||
|
|
|
||
|
|
0. Someone starts `syncplay` on a remote server.
|
||
|
|
1. User A starts `syncplay`. The program starts and runs the `mpv` player.
|
||
|
|
2. Then it connects to the remote `syncplay` instance.
|
||
|
|
3. `syncplay` observes pause and seek events reported by MPV over JSON IPC.
|
||
|
|
4. `syncplay` translates supported local events and sends them to the server.
|
||
|
|
5. The server will stream to all connected clients the same event.
|
||
|
|
6. Any connected client receives the event and sends the corresponding JSON IPC
|
||
|
|
command to its local MPV instance.
|
||
|
|
|
||
|
|
Remote seeks use a serialized, acknowledged transaction: disable delivery of
|
||
|
|
the `seek` event for the IPC connection, apply an `absolute+exact` seek, then
|
||
|
|
re-enable the event even when the seek fails. This prevents remote seeks from
|
||
|
|
being reported as new local seeks and looping through the server.
|
||
|
|
|
||
|
|
**Example cli command to run MPV**
|
||
|
|
|
||
|
|
Pay attention to the socket path. That, along with the MPV path must likely be constants in the Odin program.
|
||
|
|
|
||
|
|
```sh
|
||
|
|
/Applications/mpv.app/Contents/MacOS/mpv \
|
||
|
|
--force-window=yes \
|
||
|
|
--idle=yes \
|
||
|
|
--pause=yes \
|
||
|
|
--start=0 \
|
||
|
|
--hr-seek=always \
|
||
|
|
--keep-open=always \
|
||
|
|
--keep-open-pause=yes \
|
||
|
|
--input-ipc-server=/tmp/mpv-socket \
|
||
|
|
--input-terminal=no \
|
||
|
|
--terminal=no
|
||
|
|
```
|