m4v M4V is a file format developed by Apple for the iTunes store's content and is very similar to the MP4 file extension. M4V is supported exclusively by Apple devices. Other video formats like MP4 and MOV can be converted to M4V in order to run on Apple devices. The most common difference between the M4V and MP4 formats is that M4V offers DRM-Copyright Protection which prevents the copyright of media content. To play a DRM-protected M4V file the computer needs authorization by opening the iTunes account used for buying the media file. However, if the files are not protected by DRM, the user can just rename the file extension from M4V to MP4 in order for it to be recognized by non-apple devices.
flac The FLAC file format associated with the .flac filename extension refers to the FLAC audio encoding algorithm. FLAC is the acronym for Free Lossless Audio Codec. The algorithm is from the lossless audio compression family of formats for digital audio compression. It was developed by the Xiph.Org foundation, a non-profit organization that produces open and free to use multimedia formats, and had its initial release in 2001. Though there isn't widespread compatibility for the format as compared to similar formats such as MP3, the FLAC format enjoys some compatibility and support with in car and home stereo manufacturers as well audio playback software and portable audio devices.