Active Format Descriptor

In television technology, Active Format Descriptor or Active Format Description (AFD) is a signal that broadcasters can transmit with the picture to enable both 4:3 and 16:9 television sets to optimally present pictures transmitted in either format. Essentially, AFD is a standard set of codes sent in the MPEG video stream that provides aspect ratio and safe area information to television or set-top-box decoders. They can then use this information, together with knowledge of the display shape and user preferences, to choose a presentation mode. AFD is used in the generation of Widescreen signaling. AFDs are not part of the core MPEG standard; they are a DVB extension, which has subsequently also been adopted by ATSC.
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