I don't see any simple solution for this. In many cases due to a broken connection people need to re-download media content.

Password protection is a good idea. Just check people sharing passwords. You may write a script that analyzes IP addresses and ban account after noticing mass sharing. You should take into account that some people will be accessing content say from home and work or using different internet connections.

You may also use DRM protection. You can may one-time play licenses with it.