What is M4V?
M4V files are iTunes Video Files. The M4V file format is a standard file format for videos for iPods and PlayStation Portables developed by Apple. Nowadays, Apple's products like the iPod, iPhone, and iTunes Store, are becoming more and more popular so M4V files are becoming more commonly used.
.m4v is .mp4 files with the WRONG extension introduced by Apple for video/audio.
What is MP4
MP4 is a streamable format.
MP4 is a container format. As any other container format like AVI (.avi), RealMedia (.rm, .rmvb), QuickTime (.mov), MPEG (.mpg, .mpeg), Matroska (.mkv, .mka), OGM (.ogm) it allows you to combine different multimedia streams (mostly audio and video) into one single file.
MP4 is a file extension for the container format defined in the Systems Part of the MPEG-4 standard (ISO 14496-1).
MP4 supports all kinds of multimedia content (multiple audio streams, video streams, subtitle streams, pictures) and advanced content (called "Rich Media" or "BIFS") like 2D and 3D graphics, user interactivity, DVD-like menus.
Convert iTunes M4V files to MP4 with M4V Converter Plus
At first, you need a M4V to MP4 Converter, M4V Converter Plus will be your best choice.
M4V Converter Plus is a professional M4V to MP4 Converter. With it, you can easily convert iTunes movies purchased & rentals in .M4V format to unprotected MP4.