Hi Zenji, I think we have a small communication gap here between the following two points...
1) Protection of posts and pages to ensure only members can view the content.
2) What the member does while viewing the content.
the membership plugin protects your posts, pages, comments, categories to make sure no one can view the protected content without having a membership account. Once a member logs in, they can view the content. After a member logs in and can view the page then what they can do with the content is a different story, for example they can copy the article text or images that's on that page. How can you stop someone from saving an image that is on a web page and the person can view that page?
Anyway, the key thing to understand is that a membership plugin controls access to who can see what content. It doesn't have any control over what the member does with the content that is on the page (e.g. stop a viewer from copying a line of text on that page). All of these are upto how you have setup the content on the page.
In your case you have embedded a video I believe. eMember has no way to control what a member does with the video player. I am not an expert on video protection but I think You need to embed the video on the page using a technique so when a visitors are viewing the video they can't copy it using RealPlayer.