There are some Flex/Flash "front end" projects for Moodle. I don't know of any that are finished though. I think there's also some Moodle app projects underway.
AMFPHP is basically a translator between AS3 and PHP5, and it uses the same protocol as video. It's possible to add encryption to AMF3 streams but, at the end of the day, the downloaded files still have to be cached somewhere and a tech-savvy user will know how to get at them.
The internet was designed for sharing and it does it very well. While you can make it more difficult to take and re-use content, you can't stop it all together, and in trying to do so you may end up losing more, i.e. clients and/or students who won't or can't install software to view your content, than you gain, i.e. less loss of revenue from re-use without permission. There's also the added cost of developing the security measures and providing support for legitimate users who get stuck with your extra-complicated, locked-down system.