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.
flv The .flv filename extension and the FLV file format are associated with Adobe System's flash player. It is a container format primarily used for content delivery over the internet and other computer networks. It is an open file format and supports delivery of audio and video streams through players that are compatible with the specification. Flash video, or FLV, has been popularized on the internet by video streaming websites that encode their video in this format. Most web browsers have support for the format through web browser plugins with the exception of Google chrome which has native support for the format.