My laptop crashes during video playback! A bit of Googling and it seems like perhaps the default video output driver has a bug (Xorg Intel). A quick workaround I will try is to change the video driver to X11.

[Update] It still crashes now and then. But it happens more often now. It is definately not due to the video driver - it is much worse. It must be my laptop.

[Update #2] I think I have found the problem. It must be this. Just need a soldering iron..