You may have noticed on YouTube that you can now watch some clips in a high quality. To do this, you have to click on "Watch in High Quality" which is situated below the clip. However, the "Watch in High Quality" option is not visible for all clips but with a simple change to the video's URL, you can watch any clip in either High Definition or High Detail format.

To change the clip to High Definition, simply add &fmt=6 to the end of the clip's URL. To change the clip to High Detail, simply add &fmt=18 to the end of the clip's URL.

Here is a snapshot of a YouTube clip in default quality:

Here is the same clip in High Definition:

And finally here is the clip in High Quality:

As you can see, the sharpest results are in High Definition mode and the sound seems better too. Obviously, much depends on the quality of the original clip uploaded - you can't make a silk purse out of a pig's ear but this is a simple but effective hack to enhance your YouTube viewing.