M4V is a digital video container format developed by Apple Inc. It is pretty similar to the popular MP4 in terms of structure, but M4V files can sometimes be DRM protected. Today, M4V is the primary video format for iTunes Store videos and can multiplex together multiple audio and video data.
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AC3 is an audio format designed by Dolby Digital to offer surround sound listening. This format is available on most Blu-ray and DVD media files and is played using a Dolby Digital DVD Player. Interestingly, AC3 can be output in up to six speakers of a home stereo system. On a computer, AC3 can be opened on VLC Media Player, Apple QuickTime Player, and Windows Media Player.
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