先奉上Doom9上Dark Shikari的原文：
One of the GSOC projects for the summer was to improve B-frame decision. This was the most important project, IMO... but the student on the task just disappeared after the first week.
So I decided to do his job for him, and with akupenguin's assistance on the algorithm side of things, spent this week writing an optimal trellis-like function for B-frame decision. This algorithm provides perfect B-frame decision--or more precisely, as perfect as one can get with the current cost approximation function used.
The downside is that its a bit slower, and moreover, its speed scales linearly with --bframes. While with the previous algorithm, --bframes 16 was only minimally slower than --bframes 3, here it will be a lot slower. And this new algorithm is going to be default, since it is considerably better. The old algorithm will still be available for those who need a fast but inaccurate B-frame decision method.
So, this is a warning to all those who use --bframes 16, MeGUI and otherwise; the new B-frame decision is coming soon, and when it does, in the interests of speed you may want to lower the --bframes value to 3-5 or something otherwise reasonable.
使用方法是，用帶這個補丁的x264，命令行里什么都不加是用的傳統方法，加--b-adapt 2用新方法，--b-adapt 0是關閉b幀
