M4R is a filename extension for AAC format, which is developed by Apple Inc. It is typically used to save custom iPhone ringtones from Apple iTunes. M4R can only be created from iTunes purchased songs and is usually DRM protected. It can open on iTunes, VLC Media Player, Apple QuickTime Player, and more.
MXF (Materia Exchange Format) is an audiovisual container format developed by SMPTE. It contains full metadata and timecode support and is considered as the future standard for audio and video applications. Theoretically, MXF can streamline data between different platforms, like servers and digital cameras.
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SMPTE (Society of Motion Pictures and Television Engineers)