For some reason when I'm playing video in VLC the sound and video don't sync up, right now I've got a video playing with a -650ms gap. They do sync up in other applications for the same video, and this never used to happen but now it seems like it's happening more and more. It's usually just an inconvenience to use the keys to get it to sync up, but it is annoying.

What could be causing this/how do I fix it?