.m4v instead of .mp4

Hey there,

I know there are already forums about it, but I don't quite understand them. So when I'm exporting as .mp4, and I select export audio and export video, I only get a .m4v file I cannot open. I also tried exporting it via Media Encoder, but the process stopped twice so I gave up on it. Could anybody explain what to do, please?

P.S. I don't know if it is important, but I have Premiere Pro CC on Windows.