Suggestions for pay-per-view video lessons?

Has anyone here had any experience with any methods or services for providing video clips/lessons via a subscription or pay-per-view basis?

I'm currently using a shopping cart script that allows for basic digital downloads.
What form of video would be best for this kind of application?
Is there a better method for providing paid video content?

Any advice from your experience would be helpful.
Thanks in advance.

Hello,

This is in response to a query you made a year ago about pay per view for online lessons. It supports all media and has good management and control. Please see the below site, unlimited videos and bandwidth are provided for their pay per view cart:

http://www.MultiMediaCart.com

They also have a CDN if you need national distribution of live or H.264 HD quality video.

Author20