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.
asf The .asf filename extension refers to the Microsoft owned audio and digital video container, advanced systems format. It is a container for windows media audio and windows media video but shares the same internal structure as both WMA and WMV file formats. The format was designed with the goal of increasing efficiency in distribution of audio video files across computer networks. However, it works just as well for local system playback. The asf format forms part of Microsoft's Foundation framework. The major feature of the format is its ability to add digital rights management by providing the framework for encrypting audio and video files.