RPG Maker MV utilizes the webm and h264 codecs. From what I've read, webm is used for the browser aspect while h264 is used for mobile devices.

I haven't found anything useful for h264, but I have found a tool for webm: Firefogg for Firefox.

EDIT:
It's been a long time since I was here, but I just stumbled across a tool to encode videos to H.264. Check it out.

4878808 What even is this?

5230564
Pardon?

5230579 The encoding tools. I have no idea what these are.

5230626
They are exactly what I described. They encode videos with certain codecs. You can't just add video files to your RMMV project and expect them to work unlike previous versions, they need to be encoded in either WebM or H.264

5230647 Oh. They're for putting videos in MV projects, not simply recording off the computer screen. Got it.

5230695
Again, welcome to the group!