Media embedded in an Announcement can only be played within the Announcements tool.  Students viewing the announcement in their email will not see the video.

When duplicating a site, the contents of the Media Gallery is not copied over.  When you add content to a Media Gallery, you have published it for that specific site.  

If you intend to use the same media, you can easily import the previous Media Gallery into the new course site.  

Any playlists created in the old site will not carry over and will need to be re-created.