I was having a few problems with YouTube recently trying to get it to put up the 'Playback in HQ quality' option but after changing the setting many times it still wouldn't do it. So after having a search around other forums I came across this....
The Techno Centre - How to view any YouTube video in high quality
How to view any YouTube video in high quality
While a YouTube video may not have the "view in high quality" button shown, it may still be possible to view it in higher quality than is currently being shown. The same goes for videos that are now available to view in high definition. Tip - before watching a HD video, allow the red line to fill up the bar by pausing the video at the start.
STEP 1 - Locate the navigation (URL) bar in your browser.
STEP 2 - Make sure the URL is not highlighted.
STEP 3 - At the end of the URL, type in the following text exactly as shown (if there is already an extension on the URL, for example; &feature=related, you must remove this first - there can only be one "&" and function on the end of the videos URL):
For high quality (HQ): &fmt=18
For high definition (HD): &fmt=22
No - youtube.com/watch?v=7Toi0hinS3U&feature=related
Yes - youtube.com/watch?v=7Toi0hinS3U&fmt=18
STEP 4 - Hit enter (return) to watch the video in higher quality. Enjoy!