Audio plays back faster than video in Quicktime formats on Mac

On both my iMac and MacBook Pro, both running Mavericks, 90% of videos dependant on the Quicktime codecs / engine have an issue where the video plays fine, but audio is almost always too fast. This results in the audio being of a higher pitch and drifting further and further out of sync. It affects videos played in Quicktime, the Quick Preview in Finder and even web-based video such as in HTML5 players. It's really weird that I can't find anyone else that is having this problem, and yet it is affecting both my machines! It's really frustrating as I work with video all day, and have to preview and review everything in VLC, which plays everything fine. Any ideas at all? I'm finding so many weird bugs and quirks in Mavericks I am strongly considering downgrading back to Mountain Lion, but I am dreading having to do two complete re-installs again.