Youtube Trick: Watch Any Youtube Videos In Hi-Def Clarity

At the End of the YouTube link, just add this without space.....

" &fmt=18 " (without quotes)

After adding, your link should look like this:
Example:
http://www.youtube.com/watch?v=xxxx_xxxxxx&fmt=18

And if u wanna download video then add ".mp4" extension at the end of the link, it will automatically start download when you open the link.
Generally YouTube provides ".flv" extension file of low quality but according to my way you can download file ".mp4" of high quality.

Note:
- High Definition Clarity can be observed if u have good net speed.
- It works only for files which are uploaded with supportable extensions.(Mostly works for all files)