[manigandham]

Youtube keeps all the original source files so there's no quality loss going from one encoding to another, if that's what you were referring to.

[RDeckard]

Do they really - do you have a source on that? (no pun intended)

[jsalit]

Yep, there's mention of it on an old blog post [1], but you can verify for yourself on the Enhancements page when editing any video - there's a "Revert to original" button.

[1] - http://youtube-global.blogspot.com/2011/09/edit-your-videos-...