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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AMR (Adaptive Multi-Rate Audio Codec) is a sound compression format that is designed for speech coding. It is today widely used in UMTS (Universal Mobile Telecommunication System) and GSM (Global System for Mobile Communications). Most modern mobile phones can save short sound recording clips in AMR format and can be converted to other standard sound formats using a third-party program like Wondershare UniConverter.
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