X264多线程下码率控制算法的优化  

Optimization on Rate Control Algorithm for X264 Under Multi-threadeds

作　　者：石艺[1] 王中元[1] 胡金晖[1] 杨乘[1] 

机构地区：[1]武汉大学计算机学院国家多媒体软件工程研究中心,武汉430079

出　　处：《计算机工程》2015年第8期207-211,217,共6页Computer Engineering

基　　金：国家自然科学基金资助项目(61303114);湖北省重大科技创新计划基金资助项目(2013AAA020);贵州省科学技术基金资助项目(黔科合J字LKS[2011]1号)

摘　　要：X264编码器平均比特率(ABR)码率控制算法在单线程下,可以利用前面所有帧的实际偏差来调整量化参数(QP)。但在多线程下,当前帧之前仍有尚未编码完的帧,因此只能用部分已编码帧的实际偏差来调整QP,有可能使实际码率严重偏离目标码率。针对该问题,提出一种改进的ABR多线程码率控制方法。该方法通过当前帧之前已编码帧的实际偏差来估计未编码帧的偏差,得到类似单线程下当前帧之前所有帧的偏差,用以调整QP,达到提高多线程码率和控制精度的目的。实验结果表明,改进后视频流的实际码率更接近目标码率,码率误差最高可降低2.27%,平均码率曲线也更为平滑。In one thread,Average Bit Rate（ABR） control algorithm of X264 encoder can use the deviation of all frames to adjust Quantization Parameter（QP）.But in multi-threads,it has some frames before current one that is not encoded,so it only uses deviation of frames that have been encoded to adjust QP,which results real bit deviate target bit severely.To solve this problem,this paper proposes a method to optimize the rate control under multi-threads conditions.This method estimates the deviation of non-encoded frames based on the actual deviation of encoded frames,and achieves deviation of all frames like in one thread,then uses all frames’ deviations to adjust the current frame’s QP,and gets the goal of increasing accuracy of rate controlling.Experimental results show that the actual bit rate produced by this method is more close to the target one,rate error reduces by up to 2.27%,and the bit rate curve appears steadier than ever.

关 键 词：视频编码 平均比特率 码率控制 多线程 码率精度 

分 类 号：TP37[自动化与计算机技术—计算机系统结构]