A system, method, and apparatus for decoding a bitstream are presented herein. Symbols in the bitstream are replaced with intermediate symbols by a preprocessor. In a video decoder, a video decompression engine is used to provide decoded frames at a constant rate. However, the frames are encoded as pictures with widely varying amounts of data in a bitstream. A preprocessor replaces symbols with intermediate symbols providing the same information in a different format. The intermediate symbols are preferably simpler for decoding.