a method and apparatus for adaptively enabling a pb frames mode for video data processing . if the pb frames mode is enabled for a given pair of video pictures , and if the motion compensated prediction error for the b - picture in the most recently encoded pb frame is greater than the motion compensated prediction error for the p - picture in same pb frame multiplied by a constant , the pb frames mode is disabled for the pb frame . otherwise , the pb frames mode remains enabled . if the pb frame is disabled by the pb decision logic , it may remain disabled until certain encoding parameters are met .