DevConverter converts your video files online. Amongst many others, we support MP4, WEBM and AVI. You can use the options to control video resolution, quality and file size.
M4V is Apple developed MPEG-4 file extension that is comparable to MP4. It encodes the movies or videos from Apple iTunes store. The difference between M4V and MP4 is that M4V is protected and it can be played if anyone has a license iTunes in his computer.