Methods for rate control in an MB (macroblock) layer and apparatuses using the same

An apparatus for rate control in an MB (macroblock) layer, comprising:

• a quantizer;
• and
• a quantization parameter calculator, coupled to the quantizer, calculating a prediction MAD (Mean Absolute Difference) of a current MB of a current frame according to a real MAD of a previous MB of a previous frame, wherein the current MB and the previous MB are located at the same two-dimensional coordinates of the current frame and the previous frame, respectively, and the real MAD of the previous MB of the previous frame reflects the variances between raw data and reconstructed data of the previous MB;
• calculating a real MAD of the current MB of the current frame, wherein the real MAD of the current MB of the current frame reflects the variances between raw data and reconstructed data of the current MB;
• performing an adjustment procedure to adjust the prediction MAD of the current MB of the current frame according to the real MAD of the current MB of the current frame to obtain a final MAD of the current MB of the current frame;
• calculating a quantization parameter of the current MB of the current frame according to the final MAD of the current MB of the current frame;
• and outputting the quantization parameter of the current MB of the current frame to a quantizer, thereby enabling the quantizer to generate a compressed video stream under a rate corresponding to the current MB of the current frame.