[x264] mbtree 使用指南与源码分析

源码分析

x264源码解析：码率控制之mbtree — – – x264_macroblock_tree
x264源码解析：lookahead之frametype — x264_slicetype_path (Viterbi算法)
x264源码解析：lookahead之md/mv — — x264_slicetype_frame_cost
x264源码解析：lookahead之cost计算基础 x264_slicetype_mb_cost等
x264源码解析：mbtree propagate 计算流程
x264源码解析：mbtree qp调整

背景

Macroblock-tree derives its name from the fact that its operation can be represented as a tree structure over the macroblocks of a video where the nodes are macroblocks and the edges are prediction dependencies. The weights of the edges map to the propagate_fraction value. Despite the name, as seen above, macroblock-tree can be implemented without any mapping the lookahead into an explicit tree structure – the motion vectors and costs are sufficient to implicitly store the information for the tree.

使用

--no-mbtree Disable mb-tree ratecontrol.[not set] --rc-lookahead Number of frames for frametype lookahead [40] --qcomp <float> QP curve compression [0.60]

相关

--pbratio <float> QP factor between P and B [1.30]

控制mbtree使用的lookahead的帧数；控制mbtree作用的强度；去除目的相同的算法工具（mbtree要更灵活）

实验

选取不同复杂度视频进行测试。
为获得较为主观的质量评价结果，选择VMAF计算质量。
注意：rd性能变化和码率波动，见图。
注意：注意评价指标与主观评价的区别。（mbtree的效果可能会减弱）
注意：三张强弱标反了。。懒得换了。。注意。

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