MOV is a MPEG-4 digital video container format used on Apple’s QuickTime Player. It was developed in 1998 by Apple as the proprietary video format for Macintosh. On top of video data, MOV format can also store audio and text data, such as subtitles. It can open easily on both Macs and PCs, although Windows require 3vix codec.
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M4B is an audio filename extension for AAC format, which is developed by Apple Inc. It is mainly used on podcast and audiobook files. Typically, M4B files contain audio and other metadata like images, hyperlinks, and chapter markers. M4B files are DRM copy-protected and can be opened on Apple iTunes and QuickTime Player.