![]() ![]() Symmetric codecs are used where fast compression is important. Asymmetric codecs are used to decompress and display video in software on computers of limited power where real-time compression is not important. An asymmetric codec has a very simple decompressor, and a relatively complex compressor.Ī symmetric codec distributes the computation relatively equally between the compressor and decompressor. The computation can be distributed between the compressor and the decompressor in a particular codec. Video codec algorithms tend to be complex, implying a tradeoff between obtaining good visual quality of the decompressed output (more computation) and a frame rate that is high enough to make the motion appear smooth (less computation). ![]() This is important, as decompressed video can use a tremendous amount of disk storage and transmission bandwidth, and different applications have different quality requirements. A good algorithm allows the user to specify the tradeoff between the compression ratio and the quality of the decompressed output. Compressors for digital images or video can attain compression ratios of 30:1 or more and still produce quality reconstructed output. A lossy compressor for still images may compress its input by 10:1 with no visible distortion in the decompressed output. The first compression algorithm is lossy and the second is lossless.Ī file compressor may compress ASCII text by up to 2:1-3:1 but might not work with image data at all. In contrast, a file- or text-compression algorithm must reconstruct a file exactly from its compressed representation. Ultimedia Services Version 2 for AIX: Programmer's Guide and ReferenceĪ video codec generally introduces some distortion in the reconstructed output of the decompressor, relative to the video at the input to the compressor. ![]()
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