HTML 5 player not working.

The HTML 5 video player is not working for me. Videos start to play but then abruptly stop after about 3 seconds and the large play button is shown over the video.

Chrome 24.0.1312.57 m

Windows 8 64-bit

Radeon HD 7850 with latest drivers

I get basically the same thing. After a couple of minutes the video stops and never gets any further.

plays for 3 seconds then pauses for me, have to refresh and switch to streaming to watch a video