Method and apparatus for motion compensated video coding

Abstract

Apparatus and methods are provided for encoding video data in a manner which significantly reduces the computation performed by the video encoder and the video decoder without suffering any degradation in the perceived quality of the compressed video data. In particular, apparatus and methods are provided for determining which blocks might be zeroed out after quantization. This determination is performed after motion estimation, the classification of the frame as either an I frame, P frame, or a B frame, and the determination of a quantization step size (QP) for the block, but before DCT. If a given block is determined to be a “zero” quantized block, then the DCT, quantization, zig-zag scan and variable length coding steps are omitted, and a variable length code output is provided indicating that the block B is a “zero” quantized block. The present invention determines which blocks might be zeroed out after quantization by using one or more key features of the motion compensated blocks which will help in classifying these blocks into zero and nonzero blocks. Examples of these features include the mean absolute value of a block, the mean square error of a block, the block variance, the mean absolute difference of a block, and the maximum value in a block. Each feature is provided with a predetermined threshold that has been experimentally calculated.