The Alpha architecture has added several new instructions called Motion Video Instructions (MVI) that can be used to accelerate the performance of key algorithms used in emerging motion video technologies. The criteria for selecting these new instructions are based on the fundamental premise that it is important to keep the Alpha architecture “clean ” in order to facilitate extremely fast circuit implementations of the architecture. In order to be added, a new instructions must passed two critical tests: the benefits provided must span multiple generations; and, the benefits must be material. The MVIs for the Alpha architecture were motivated by the desire to perform high quality software motion video encoding using the prevalent ISO/ITU video compression standards. The standards that were addressed were MPEG 1 , MPEG 2 (also known as H.262) , H.261 , and H.263. These are all motion compensated discrete cosine transforms (DCT) and inverse discrete cosine transforms (IDCT) based compression methods. Thus, a common set of hardware features are able to accelerate the computations for each of these standards. MPEG 1 is targeted at storing 74 minutes of CD quality audio and VHS quality video on a single speed CD ROM. MPEG 2 is a scaleable compression standard that is applicable to low resolutio
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