learn theory from a book/website where you can read the content as many times as you like and at your own pace - it'll be worded better and more complete as it won't be someone trying to squeeze a load of information into a few minutes' worth of video

just my opinion though
A really good youtube channel is Creative Guitar Studio with Andrew Wasson he is great at explaining things and showing how to practice and apply music theory
I think it's pretty hard to learn theory on Youtube as most channels don't have a set beginning and ending so it makes it kind of hard. But, I came across this channel; Karen Cuneo Ramirez. She teaches theory using the piano, but you'll understand it all the same. She's a fantastic teacher. Best theory I've come across on Youtube.
Andrew Wasson is a hero. You can check out one of his vids and spend weeks working on the content.
I make backing tracks for bass and guitar players. Check 'em out here.
I've seen so many, including Andrew. Have to say, Pebber Brown is the Best.

His lessons start with the most basic to advanced.

Last edited by gravitycure at Apr 10, 2015,
John Oswin's YouTube series was what did it for me. I found his explanations absolutely, brilliantly clear. I learned more music theory by watching his videos than everything else put together.