Your two questions: 1. What are the licensing fees/restrictions surrounding this? Is it a pay-per-view scenario?

As noted in the other post, you will have to purchase rights from ASCAP, BMI, etc. My question is, why do you want to use copyright music on your videos in the first place? There's a giga-ton of free music available.

2. Does anyone know of any clearing houses or services that actually license content like this?

As mentioned BMI, etc. You purchase the rights and depending upon the sound track you want to use it will cost you $X.00. It varies too much to know. Sometimes it's worth it, worth it to pay the fee because that particular voice, that particular musician will add significant value to your video. Then you buy. The next question becomes what kind of rights do you want to buy? It might be seen as a pay-per-view model. Depends.

When you have that all done, the project finished, check out www.muzility.com We serve the videomaker.

Peace,
Calius