## Line 21 Decoder

The Line 21 Decoder filter takes Line 21 data (closed captions) and decodes it to produce a bitmap of media type MEDIATYPE_VIDEO. The output can then be rendered through a video renderer or mixed in a video mixer, such as the Overlay Mixer.

The Line 21 input data to the filter can be either of two forms: byte-pair data that comes on Line 21 of a video frame or feed, or DVD Line 21 data. For every group of pictures (GOP) in the DVD video stream, there can be a user data packet that has that particular GOP's header information and Line 21 data.

The Line 21 Decoder filter supports the IAMLine21Decoder and IBaseFilter interfaces externally, and the IAMovieSetup interface internally.

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