Method and system for video encoding using a variable number of b frames

Abstract

An effective method for dynamically selecting the number of I, P and B frames during video coding is proposed. Short-term look-ahead analysis of a video sequence yields a variable number of B frames to be coded between any two stored pictures. The first picture of a group of frames (GOF) may be coded as a B picture. Motion speed is calculated for each picture of the GOF with respect to the first picture of the GOF. Subject to exceptions, as long as the subsequent pictures exhibit motion speeds that are similar and motion vector displacements that are co-linear with those of the first picture in the GOF, they may be coded as B pictures. When a picture is encountered having a motion speed that is not the same as that of the first picture in the GOF, the picture may be coded as a P picture.

1 - 32 . (canceled) 
     
     
         33 . A storage device storing coded video data generated according to a method comprising:
 from a sequence of video data, determining a motion speed between a first picture and a reference picture;   for each consecutive picture in a plurality of temporally adjacent pictures following the first picture in the sequence, until a termination condition is met:
 determining a motion speed for the respective picture; 
 coding the respective picture as a B picture if its motion speed is consistent with the motion speed of the first picture; 
   when the termination condition is met, coding a picture as a P picture; and   storing coded data of the B pictures and the P picture in the storage device.   
     
     
         34 . The storage device of  claim 33  wherein the motion speed for the respective picture is consistent with the motion speed of the first picture where a motion speed error does not exceed a predetermined threshold, the motion speed error calculated as a degree of difference between a motion vector of the respective picture and a motion vector of the first picture. 
     
     
         35 . The storage device of  claim 33  wherein said termination condition comprises detecting a scene change. 
     
     
         36 . The storage device of  claim 35  wherein a scene change is detected where a correlation coefficient between two temporally adjacent pictures is below a predetermined threshold. 
     
     
         37 . The storage device of  claim 33  wherein said termination condition comprises a number of consecutive pictures assigned a coding mode of a B picture exceeds a predetermined threshold. 
     
     
         38 . The storage device of  claim 33  wherein said termination condition comprises detecting a picture is the last picture of the video sequence. 
     
     
         39 . The storage device of  claim 33  wherein the storage device is a buffer memory at an encoder.