Why do some people hate B-pictures?
A. Computational complexity, bandwidth, end-to-end delay, and picture buffer size are the four B-frame Pet Peeves. Computational complexity in the decoder is increased since some macroblock modes require averaging between two block predictions (macroblock_motion_forward==1 && macroblock_motion_backward==1). Worst case, memory bandwidth is increased an extra 15.2 MByte/s (assuming 4:2:0 chroma_format at Main Level), not including any half pel or page-mode overhead) for this extra directional prediction. To really rub it in, an extra picture buffer is needed to store the future reference picture (backwards prediction frame). Finally, an extra picture delay is introduced in the decoder since the frame used for backwards prediction needs to be transmitted to the decoder and reconstructed before the intermediate B-pictures in display order can be decoded. Cable television have been particularly adverse to B-frames since, for CCIR 601 rate video, the extra picture buffer pushes the decoder D
