Apparatus and method for fast intra/inter macro-block mode decision for video encoding

1. A method for fast video encoding on a mobile device, comprising:

estimating a rate-distortion cost for a plurality of predictors for coding a video;

selecting a predictive coding mode for the video based on a minimization of the rate-distortion cost;

coding the image using the predictive mode associated with the minimum rate-distortion cost;

evaluating statistical information across the plurality of predictors collected from previous rate-distortion estimations; and

providing an early termination for computing rate-distortion costs that exceed a threshold based on the statistical information;

wherein the estimating a rate-distortion cost is performed across a plurality of intra macro-block modes and a plurality of inter macro-block modes for reducing computational complexity associated with rate-distortion costs of intra macro-block modes;

wherein estimating a rate-distortion comprises:

computing an inter rate-distortion cost for coding using the inter macro-block modes;

setting the minimum rate-distortion cost to the inter rate-distortion cost; and

comparing the inter rate-distortion cost to a first threshold;

wherein comparing the inter rate-distortion cost comprises:

if the inter rate-distortion cost is greater than the first threshold, then computing a first intra rate-distortion cost using a first intra macro-block mode for generating a coarse approximation of the rate-distortion cost; and

if the inter rate-distortion cost is less than the first threshold, then not selecting the first Intra macro-block mode;

the method further comprising:

computing a second intra rate-distortion cost using a second Intra macro-block mode;

comparing the second intra rate-distortion cost to the minimum rate-distortion cost and updating a minimum rate-distortion cost based on the comparing;

wherein updating includes: setting the minimum rate-distortion cost to the second intra rate-distortion cost if the second intra rate-distortion cost is less than a current minimum rate-distortion cost;

the method further comprising:

comparing an approximated first intra rate-distortion cost to a second threshold; and

if the approximated first intra rate-distortion cost is less than the second threshold, then refining the approximated first intra rate-distortion cost; and

if the approximated first intra rate-distortion cost is greater than the second threshold, then not updating the approximated first intra rate-distortion cost in view that the first intra mode is unlikely to be an optimal macro-block.

2. The method of claim 1 , wherein estimating a rate-distortion cost includes:

generating a coarse approximation of the rate-distortion cost of a predictor;

comparing the approximated rate-distortion cost to a threshold; and

determining whether to refine the estimation of the rate-distortion cost based upon the comparison,

wherein the rate-distortion cost is associated with a macro-block coding mode or type in a video coding system.

3. The method of claim 2 , further comprising:

repeating the generating, comparing, and determining for the plurality of predictors; and

selecting the predictor associated with the lowest rate-distortion cost.

4. The method of clam 1 wherein the first threshold can be adjusted dynamically.

5. The method of claim 1 further comprising:

comparing the inter rate-distortion cost, a first intra rate-distortion cost, and the second intra rate-distortion cost; and

selecting a predicting mode corresponding to lowest rate-distortion cost;

wherein the predicting mode is an Inter macro-block mode or an intra macro-block mode.