threads
Default: auto (frame based threads: 1.5 * logical processors, rounded down; slice based threads: 1 * logical processors)
Enables parallel encoding by using more than 1 thread to increase speed on multi-core systems. The quality loss from multiple threads is mostly negligible unless using very high numbers of threads (say, above 16). The speed gain should be slightly less than linear until you start using more than 1 thread per 40px of vertical video, at which point the gain from additional threads sharply decreases.
x264 currently has an internal limit on the number of threads set at 128, realistically you should never set it this high.
Recommendation: Default
See also: thread-input, sliced-threads
[edit] sliced-threads
Default: off
Enables slice-based threading. This threading method produces worse results than the default method both compression and efficiency-wise, but adds no encoding latency.
The maximum number of sliced threads is MIN( (height+15)/16 / 4, 128 )
Recommendation: Default (off), unless you are doing some sort of realtime streaming or low latency is important.
threads增大会带来编码速度的上升 但质量的损失可以忽略不及(除非16线程以上)
用sliced-threads可以降低延时的 但sliced-threads好像是处理实时视频流编码的 压缩和效率上都不如默认的好 传网上的话效果只能自己试试了
手动调低threads的效果就不清楚了
