Once again I would suggest buying and using video loops from videohive, as they are great hd visuals and you can also send people there via refferal link from your youtube video and maybe get a referral credit from people that need stock footage. Probably same crowd that is searching out royalty free music.
When you buy a videohive video you get a license as well in case youtube comes knocking. It would be a shame to get your promo video ranked and then have to take it down. Another site is bottled video. Com. You can use there stock video free with just a credit. But no hd quality stuff, like I see on videohive. Even if you get one referral from your video you pay off the low video hive purchase fee. Always looks better to use professional looking things.