Depending on whether the file is copy-protected, you have several options for viewing it: [Updated] What is M4V File Format & How to Play M4V Video
The M4V format is closely related to the more common MP4 format but is specifically optimized for the Apple ecosystem. 4501731.m4v
Not all M4V files are protected. Tools like HandBrake often use ".m4v" as a default extension for standard MP4 videos to ensure compatibility with Apple features like chapter markers and AC3 audio. How to Open "4501731.m4v" Depending on whether the file is copy-protected, you