Embed or Link high quality YouTube videos.
First you want to set your youtube settings when you view the site (signed in or not) So before you copy the embed code, you want to set your default settings In your account settings section on your play back to.

OK, for linking a High Quality video. Basically all you have to do is add: "
&fmt=18" or "
&fmt=22" with out the quotes to the end of both URL's inside the embed code. (18 is the 480x360 version, and 22 is the 720p version.)
Example:
http://www.youtube.com/watch?v=Jv8QlB64aMc&fmt=18
You can also do this when it comes to Embedding a High Quality video.
Just add "
&ap=&fmt=18" to the end of both URLs in your embed code.
Example:
<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/Jv8QlB64aMc&hl=en&fs=1&ap=&fmt=18"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/Jv8QlB64aMc&hl=en&fs=1&ap=&fmt=18" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="425" height="344"></embed></object>
So in short, just basically copy the added codes or type it and then paste it at the end of the URL's.

Sources: B.SkiLLs @ Xtreme Stylez Tutorials, Download Squad as a reminder to post Pic sample.