I tried searching but I couldn't find this one specifically.
When using the latest Chromium (version 37.0.2062.120 Ubuntu 14.04 (281580)) HTML5 video with audio will be out of sync. Usually, the audio plays further ahead than the video. I've tested it with YouTube HTML5 video and with loading an HTML5 video with audio directly into the browser.
It's a very noticeable difference, usually a whole second or more of latency.
I thought the problem might have been due to my audio backend, but I'd prefer not to remove Pulseaudio if at all possible.