From what I have read, it's doesn't fully mirror, bu some apps will.
I think the OP is confused about mirroring and is asking about airplay. You can use airplay to watch youtube video's but an ipad 1 can't mirror its display to any atv. It just doesn't have the specs to manage that.
To the OP is there a reason you don't just use youtube on the atv3 itself rather then airplay from the ipad.
Thanks. I'm trying to figure this out for my 80 year old dad who just recently became addicted with You Tube. If you don't mind helping me out, if my dad is using his iPad on the couch, does it show up on the tv through Apple TV. Sorry but I feel like I'm missing something.
The iPad 1 mirrors? I thought that was an iPad 2/iPhone 4S feature. No?