Converting .mp4 videos to .m4v format
Converting MPEG-4 Videos directly to iTunes Video Files (.mp4 to .m4v conversion) is certainly possible and quite straightforward.
The easiest way is to simply try and rename your MP4 file to M4V.
Should that not work, use one of several video editing programs or (online) conversion tools, such as Adobe Premiere Pro or Freemake Video Converter, which allow users to import MP4 videos and export them in M4V format.