Why do some people hate B-frames ?
A. Computational complexity, bandwidth, delay, and picture buffer size are the four B-frame Pet Peeves. Computational complexity in the decoder is increased since a some macroblock modes require averaging between two macroblocks. Worst case, memory bandwidth is increased an extra 15.2 MByte/s (4:2:0 601 rates, not including any half pel or page-mode overhead) for this extra prediction. An extra picture buffer is needed to store the future prediction reference (bi-directionality). Finally, extra delay is introduced in encoding since the frame used for backwards prediction needs to be transmitted to the decoder before the intermediate B-pictures can be decoded and displayed. Cable television (e.g. — more like i.e.– General Instruments) have been particularly adverse to B-frames since, for CCIR 601 rate video, the extra picture buffer pushes the decoder DRAM memory requirements past the magic 8- Mbit (1 Mbyte) threshold into the evil realm of 16 Mbits (2 Mbyte)…. although 8-Mbits is f
Computational complexity, bandwidth, delay, and picture buffer size are the four B-frame Pet Peeves. Computational complexity is increased since a some macroblock modes require averaging between two macroblocks. Worst case, memory bandwidth is increased an extra 16 MByte/s (601 rate) for this extra prediction. An extra picture buffer is needed to store the future prediction reference (bi-directionality). Finally, extra delay is introduced in encoding since the frame used for backwards prediction needs to be transmitted to the decoder before the intermediate B-pictures can be decoded and displayed. Cable television (e.g. General Instruments) have been particularly adverse to B-frames since the extra picture buffer pushes the decoder DRAM memory requirements past the magic 8-Mbit (1 Mbyte) threshold into the realm of 16 Mbits (2 MByte) for CCIR-610 frames (704 x 480), yet not for lowly 352 x 480. However, cable does not realize that DRAM does not come in convenient high-volume (low cost)
