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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AA (Audible Audio) is an audio container format with a .aa filename extension and is used to store audiobooks. It can contain audiobook features such as spoken-word audio, bookmarks, chapter markers, and more. This format is supported by portable devices like Apple iPod, Amazon Kindle, ScanDisk Sansa, Creative Zen, and more.
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