Is there a license / royalty free DRM available for protecting and distributing video content?
There are not many use cases where using DRM is a viable practice - there is no way to "enforce" trust and DRM only penalize people that should be trusted ... remember there is no way to protect data from the Analog Hole once you decided to share them with an untrusted party.
Anyway you can always have a look at the DReaM project which is not very active these days (plus, its website does not seem responsive, for me it timeouts 4 times out of 5). You may find some more recent information at openmediacommons.org.
A freeware DRM scheme won't work in Microsoft's Windows Media Player.
So if you want people to use your content with this player, you need to use Microsoft's own DRM.
The doc give the impression that the SDK is free, but I'm sure that you'll pay something to Microsoft somewhere along the way.
DRM is encryption. The way encryption works is that you have a key that can open the lock, and that key is given only to people you want to be able to access the content, and kept away from people who you don't want to access it.
The reason that DRM is flawed is that the person you want to access the content and the person you want to keep access from is the same person. It just doesn't make any sense. The only way it sorta-kinda works is that keys are given to a tool that is restricted in its use. But that tool has to keep the key away from the user. In order to use that tool, you have to use a lock that matches one of its keys.
At this point you ask, "why can't I just add my own key?" And you might be able to. But the only way to get that key into the tool is to give it to he person you're trying to keep it away from. It's like asking a burglar to give your housekeys to your roommate for you.