A bit-rate control method for low bit-rate video coding based on high bit-rate period emphasis

Abstract

A bit-rate control method for high-quality video distribution at low bit rates is proposed. That method involves first encoding the video signal with predetermined coding parameters and then dividing it into three periods of high, medium, and low coding rates. The periods of high coding rate are allocated bit rates equal to or greater than the transmission bit rate t o improve image quality. Moreover, the bit rate for periods of low coding rate is lowered so that the bit rate allocated t o periods of high coding rate can be made greater. Preliminary experiments show that this high-coding-rate period emphasis method is consistent with the characteristics of human vision. The results of subjective tests on image quality that were conducted on a video distribution system using the proposed method show that for a transmission bit rate of 128 kbps with the proposed bit rate control method, the image quality is equivalent t o a fixed bit rate that is approximately 1.9 times higher.

A two-layer real-time rate control algorithm based on lagrange optimum algorithm

“…Its rate control algorithm named after the H.264 test model 5(TM5) is developed from test model 5 of MPEG2. TM5 consists of four steps [2] , namely, allocating propel bits to each frame and initiating the quantization parameters; exploiting rate-distortion(R-D) model to choose the encoding pattern and estimate motion; updating Q value according to buffer's states and encoding bits; using R-D model to choose new motion vector (MV) and Macro block's encoding pattern.The quantization parameter Q used by the H.264 rate control algorithm and R-D model introduces the emulation problem [3] below: when performing R-D optimization to frame, the sum of absolute differences (SAD) of the current frame must be calculated first to choose the quantization parameter; while SAD can be only obtained after the R-D optimizing process. Because of this disadvantage of the H.264 draft, it is not suitable for real-time transmission.…”

“…Its rate control algorithm named after the H.264 test model 5(TM5) is developed from test model 5 of MPEG2. TM5 consists of four steps [2] , namely, allocating propel bits to each frame and initiating the quantization parameters; exploiting rate-distortion(R-D) model to choose the encoding pattern and estimate motion; updating Q value according to buffer's states and encoding bits; using R-D model to choose new motion vector (MV) and Macro block's encoding pattern.…”