1. A method for transcoding an input video to a lower spatial resolution, comprising the steps of: decoding the input video into pictures, each picture including a set of macroblocks; filtering each picture to a downscaled picture having a lower spatial resolution; selecting a quantization scale for each macroblock in the downscaled picture; generating a set of motion vectors for each macroblock in the downscaled picture; determining a multiplier value based on the quantization scale for each macroblock in the downscaled picture; selecting one of a plurality of encoding modes for each macroblock in the downscaled picture according to the quantization scale, the motion vectors, and the multiplier value; and encoding the each macroblock in each downscaled picture according to the quantization scale, the selected encoding mode, and the set of motion vectors to produce an output video having a lower spatial resolution that the input video.