Microsoft Video 1 or MS-CRAM is an early lossy video compression and decompression algorithm (codec) that was released with version 1.0 of Microsoft's Video for Windows in November 1992. It is based on MotiVE, a vector quantization codec which Microsoft licensed from Media Vision. In 1993, Media Vision marketed the Pro Movie Spectrum, an ISA board that captured video in both raw and MSV1 formats (the MSV1 processing was done in hardware on the board).
Microsoft Video 1 operates either in a 8-bit palettized color space or in a 15-bit RGB color space. Each frame is split into 4×4 pixel blocks. Each 4×4 pixel block can be coded in one of three modes: skip, 2-color or 8-color. In skip mode, the content from the previous frame is copied to the current frame in a conditional replenishment fashion. In 2-color mode, two colors are transmitted, and 1 bit per pixel is used to select between the two colors. In 8-color mode, the same scheme applies with 2 colors per 2×2 block. This can be interpreted as a 2-color palette which is locally adapted on either a 4×4 block basis or a 2×2 block basis. Interpreted as vector quantization, vectors with components red, green, and blue are quantized using a forward adaptive codebook with two entries.
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