AIiF (Apple Interchange File Format/Audio Interchange File) is a sound format used on Mac OS X. It comes with a .aiif filename extension and .aif when used on Windows. An AIF file features raw sound data like sample rate, bit depth, and channel (mono/stereo). This file format is also accepted on most CD writers.
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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.