VRO is a digital audiovisual file format for streaming DVD recordings. When generated, this file usually comes with an IFO file for providing the location information of the VRO file. Generally, VRO is like a collection of VOB files. However, fragmented VROs are not widely supported.
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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.