M4V is a video container format developed by Apple that is very similar to MP4 but often includes DRM copy protection . Because of these restrictions, downloading and playing "final" M4V files can sometimes be tricky outside of the Apple ecosystem.
Use QuickTime Player or iTunes, which are the native applications for this format.
If you are downloading a non-protected M4V from a website, most modern browsers will play the video in a tab rather than downloading it. To force a download, right-click the video link and select "Save Link As..." . Opening M4V Files
Most M4V files are downloaded directly through iTunes or the Apple TV app. To download purchased content, ensure your computer is authorized with your Apple ID.