Method and apparatus for rate control for constant-bit-rate-finite-buffer-size video encoder

Abstract

A method and apparatus for rate control for a constant-bit-rate finite-buffer-size video encoder is described. Rate control is provided by adjusting the size of non-intra frames based on the size of intra frames. A sliding window approach is implemented to avoid excessive adjustment of non-intra frames located near the end of a group of pictures. A measurement of “power” based on a sum of absolute values of pixel values is used. The “power” measurement is used to adjust a global complexity value, which is used to adjust the sizes of frames. The global complexity value responds to scene changes. An embodiment of the invention calculates and uses L1 distances and pixel block complexities to provide rate control. An embodiment of the invention implements a number of bit predictor block. Predictions may be performed at a group-of-pictures level, at a picture level, and at a pixel block level. An embodiment of the invention resets a global complexity parameter when a scene change occurs.

What is claimed is: 
     
         1 . Apparatus for rate control for a constant-bit-rate finite-buffer-size video encoder comprising:
 a preprocessing stage for determining a power value based on pixel values of only a first frame; and   a group-of-pictures-level rate control block operatively coupled to the preprocessing stage to receive the power value and to provide a target quantizer step size used to provide rate control for the video encoder;   wherein the group-of-pictures-level rate control block causes an adjustment of sizes of non-intra frames based on expected sizes of future intra frames.   
     
     
         2 . The apparatus of  claim 1  wherein the preprocessing stage updates the power value for each subsequent picture being encoded. 
     
     
         3 . Apparatus for rate control for a constant-bit-rate finite-buffer-size video encoder comprising:
 a prediction error image block to determine L1 distances according to sums of absolute differences;   a picture-level rate control block operatively coupled to the prediction error image block to receive the L1 distances and to produce a target quantizer step size for a pixel block; and   a complexity estimator block operatively coupled to the prediction error image block to determine non-intra pixel block complexity values and intra pixel block complexity values.   
     
     
         4 . A method for rate control for a constant-bit-rate finite-buffer-size video encoder comprising:
 obtaining a prediction error frame including a plurality of pixel-level error values;   calculating a sum of absolute values of the pixel-level error values for a pixel block;   calculating an expected number of bits for the pixel block based on the sum of the absolute values, and   using the expected number of bits for the pixel block to obtain constant-bit-rate video encoding.   
     
     
         5 . The method of  claim 4  wherein using the expected number of bits for the pixel block to obtain constant-bit-rate video encoding further comprises:
 calculating an expected number of bits for a frame in which the pixel block is located; and 
 using the expected number of bits for the frame to obtain constant-bit-rate video encoding. 
 
     
     
         6 . The method of  claim 5  wherein calculating the expected number of bits for the frame further comprises:
 summing the expected number of bits for the pixel block for all pixel blocks in the frame. 
 
     
     
         7 . A method for rate control for a constant-bit-rate finite-buffer-size video encoder comprising the:
 predicting a relationship between a quantizer scale factor and a number of encoded bits of a pixel block based on a known relationship in previous pixel blocks of a same type; and   using the quantizer scale factor to control a pixel block level rate of the video encoder.   
     
     
         8 . The method of  claim 7  wherein using the quantizer scale factor to control the pixel block level rate of the video encoder further comprises:
 using the quantizer scale factor together with a sum of absolute values of pixel-level error values to control the pixel block level rate of the video encoder. 
 
     
     
         9 . The method of  claim 7  wherein predicting the relationship between the quantizer scale factor and the number of encoded bits of the pixel block further comprises:
 predicting a first relationship between the quantizer scale factor and a first number of encoded bits of a first type of pixel block based on a first known relationship in previous pixel blocks of the first type; and 
 predicting a second relationship between the quantizer scale factor and a second number of encoded bits of a second type of pixel block based on a second known relationship in previous pixel blocks of the second type. 
 
     
     
         10 . A method for rate control for a constant-bit-rate finite-buffer-size video encoder comprising:
 calculating a prediction for a number of bits encoded for a pixel block based on a sum of absolute values of pixel-level error values, a pixel block complexity, and a quantizer scale factor;   using the prediction for adjusting the quantizer scale factor to meet a targeted picture-level number of bits.