M4V files

What are M4V files? 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. The common use of M4V files is due to the popularity of Apple's iPod, iPhone, and iTunes Store. M4V files format is based on the MPEG-4 Part 2 compression, which is a global multimedia standard and this standard was introduced to provide optimized video podcasts for the video iPod.

.M4V files and .MP4 files are both MP4 files, and  the difference is that M4V files are associated by deafult to open in iTunes, while MP4 in Quicktime.