Please post some more info on your system specs:
Processor, RAM, Video Card, etc. and how you are connected to the internet.
Also, is VDPAU displayed anywhere on the screen when you press 'i' on the keyboard while the video is playing? If not try 'forcing' it by toggling "Enable hardware assisted decoding when possible" in Settings > Media > Advanced. Once it is unchecked the line below it will no longer be dim. Make sure it is set to VDPAU and then restart the video.