Customizing an embeded YouTube url in WordPress

[paaljoachim]

I made this tutorial:
http://easywebdesigntutorials.com/customizing-a-video-embed-in-wordpress/

Containing how to align an embeded url added into a post or page in WordPress.
As well as how to change the size of the embeded video.

I feel like the tutorial is missing important information that people who use WordPress could benefit from.
What code would I need to add into the functions.php file to show a HD version of a video?
What about auto starting a video?
Other information that would be good to add?

It would be great to have code added to the functions.php file to gather code into one place.
Thanks!