[Williams Smith]

First of all, if your M4V video is DRM-free, you can easy to put your M4V video to final cut pro, but whilst your M4V is DRM-protected, you need some tool like iTunes M4V Converter for helping you with converting M4V to edit in final cut pro. The following message will help you better in operating.
https://www.tunefab.com/m4v-converter/
https://www.tunefab.com/tutorials/m4v-final-cut-pro.html