-Are you using the latest version of iMovie?
-iMovie doesn't create playable DVDs from its projects. You can share the movie files via email, Internet, etc. You would need another piece of software to author DVDs that are playable on a DVD player - which used to be the now discontinued Apple iDVD application.
Hi, I also have this problem. I am trying to make DVDs to play on a DVD player from Mp4 files I recorded on my go pro. I have a macbook pro with El Capitan. Do you have any suggestions for what to use?