jwatzman / vlc-sync

Syncronization extension for VLC to keep two people playing the same video in sync over the internet

About

VLC does not have a good way for two people to watch the same video at the same time and automatically keep the two viewings in sync over the internet. It does have the "netsync" module, but that seems designed for a LAN where one person streams a video and the rest recieve and sync on the stream. All that really needs to happen is for the two people to open the same video file and for VLC to periodically transmit timecodes between the two in order to keep in sync. That's exactly what this VLC extension does -- it simply transmits timecodes from a server to a client; if the client is more than one second out of sync, the client seeks to that timecode.

Installation

The client should work on any OS that VLC supports. The server will not work on Windows because it needs to call the "sleep" shell command (yes, this is really idiotic and should be fixed -- patches accepted). Unfortunately, the OS X default interface, as of VLC version 1.1.6, does not allow running extensions. It is possible, though tricky, to build the QT4 interface on OS X and run extensions that way. I hope to post instructions to the VLC forum shortly.

The only actually tested configuration is with an OS X server and a Windows XP client.

To install, drop sync-server.lua and/or sync-client.lua as appropriate into the VLC extensions directory. Note that the port number is hardcoded in both the client and the server, and the server location is hardcoded in the client. You will probably want to at least change the server location that is hardcoded in the client.

The extensions directory is located at:

• OS X systemwide: /Applications/VLC.app/Contents/MacOS/share/lua/extensions/
• OS X current user: ~/Library/Application Support/org.videolan.vlc/lua/extensions/
• Linux systemwide: depends upon distro
• Linux current user: ~/.local/share/vlc/lua/extensions/
• Windows systemwide: C:\Program Files\VideoLan\VLC\lua\extensions\
• Windows current user: I have no idea

Usage

The client and the server both begin playing the same video. While the video is playing (possibly paused if needed), the server activates the server extension from the View menu. A dialog will pop up if there is an error, but nothing will happen otherwise. Then the client activates the client extension the same way; again, a dialog will pop up only if there is an error. Both videos should now be approximately in sync.

Note that the server might need to have the sync port forwarded on the router if there is a NAT between the two machines. Since the sync is maintained via seeking, if the video has issues seeking the client might get very sad.

Known Issues

WFM, YMMV, etc. Patches welcomed.

• server can only accept one connection
• no way to kick server out of accept()
• client and server do not always properly detect remote disconnects
• client and server should run in a separate thread, if possible?
• no security whatsoever
• does not ensure you are playing the same vieo on each side
• conflates master/slave with server/client
• client connects to a hard-coded location
• pausing on either end can create weird results until unpaused
• does not deal at all with latency jitter
• server does not actually block, but runs "sleep 1" in a loop
• code is pretty crappy

vlc-sync's Issues

"Extension 'Sync Server' does not respond."

First of all, thank you for this extension, not sure why I didn't find this sooner.

I'm using VLC media player 2.0.3 'Twoflower' and whenever I use your extension it eventually times out and says, 'Extension "Sync Server" does not respond. Do you want to kill it now?' This appears on both machines.

Otherwise, still syncs that one time before the error.