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Video Compression

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Current revision as of 07:05, 27 July 2007

Compression uses mathematic algorithms to store large amounts of digital data in a relatively small amount of space. There are two main kinds of compression, lossy, and loss-less. Loss-less compression includes the RAR/ZIP format, where the original data is compressed, and when de-compressed, the data has not changed. Lossy compression includes most video compression formats, such as JPEG, MPEG-1/2/4 - this means that when the digital data is compresssed and de-compressed, it is no longer the same as the original (usually denoting a loss of quality).

Uncompressed video will store the complete information for each frame. Compressed video take into account that subsequent frames contain very little change, and that by referencing an earlier complete frame (key frame), you only need to store the differences between these two frames, rather than two complete frames. Plus each frame is compressed in the same way JPEG files are compressed, by removing information that the human eye does not notice and by using mathematical functions to approximate elements in the frame (the inaccuracies in the approximation show up as compression artifacts). Please refer to Frames for an explanation of the different types of video frames used in video compression.