We found out that Chrome does not download HTML5 videos at full speed. This creates buffering and erratic behavior when the current speed of your connection is not great. Unfortunately, the network quality is always changing and slow speeds can happen.
We have added the option of forcing a Flash player instead of the HTML5 player. You can switch to the alternative player from Account -> Settings -> Playback Settings. The Flash player always downloads the video file at full speed.
Another option is switching to Firefox.