Webcams generate a stream of images that, when shown in rapid sequence, produce the illusion of continuous motion. The AVI specification is a subset of Microsoft's Resource Interchange File Format (RIFF) designed to hold audio and video data. Every AVI file begins with the characters, "AVI_" (where the underscore represents a space). Cascaded headers define the internal structure of the file and its contents. Inside an AVI file, however, the image data are stored in "chunks" that have a structure similar to that of BMP images.
For processing, an AVI is normally split into a sequence of individual 24-bit color images that are processed individually and reassembled into an enhanced AVI file, stacked into a single image, or selected on a frame-by-frame basis and then stacked into a single image. For generating movies from CCD images, a sequence of images can be processed, registered, and then combined in order and placed into an AVI file.
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