关于新版本的x264的功能

xuxing24

早上更新了下megui， x264的版本变成了1649版了，设置程序了多了V U I （full range），请问各位大大这个功能有什么作用，求解

还有slow-firstpass对质量的影响有多大

dgwxx

电视对应的颜色范围是亮度信号16～235（16是纯黑，235是纯白，0和255是同步信号），色差信号是-112～+112（为了描述方便通常写作16～240），这个范围称作TV Range（也叫601 range）。
而电脑的显示器显示颜色的范围是0～255（0是纯黑，255是纯白），这个范围称作PC Range（也叫full range）。
所以在电脑上播放视频的时候要将对应电视的信号范围重新映射至电脑对应的范围，这个过程成为YC伸张。不然你看到的图像就是灰蒙蒙的。

但现在问题出现了，如果你编码的图像正好是PC Range，播放过程中就不需要再进行伸张了。所以x264给出了这个选项，你可以告诉x264你正在编码的是PC Range还是TV Range。x264会在输出的文件中加入一个旗标（默认是TV Range），告诉播放器/解码器这个文件是哪个range，以便解码器和播放器进行正确的处置。
可是，现在似乎没有那个解码器/播放器会去确认这个标记。就是说，这个参数就算你设置了也多半没用。

slow-firstpass好像会提高码率控制的准确性，不过个人认为没这个必要。请自行评估机器性能和slow-firstpass的性价比。

akiduki

How to use VUI parameters have been long appeared in the x264 sourcecode, showing in /doc/vui.txt, you can refer that.

Here is a quote from vui.txt on using full range

4. Full Range
--------------

* What is it?
    Another relic from digitizing analog video. When digitizing analog video
    the digital representation of the luma and chroma levels is limited to lie
    within 16..235 and 16..240 respectively. Playback equipment usually assumes
    all digitized samples to be within this range. However most DVDs use the
    full range of 0..255 for luma and chroma samples, possibly resulting in an
    oversaturation when played back on that equipment. To avoid this a range
    correction is needed.

* How do I use this option?
    If your source material is a digitized analog video/TV broadcast it is
    quite possible that it is range limited. If you can make sure that it is
    range limited you can safely set full range to off. If you are not sure
    or want to make sure that your material is played back without
    oversaturation, set if to on. Please note that the default for this option
    in x264 is off, which is not a safe assumption.
   
* Should I use this option?
    Yes, but there are few decoders/ media players that distinguish
    between the two options.

Though most of us didn't use that so often.

Sorry I can't type Chinese in my company.

yadong1985

slow-firstpass开了会要命，非常慢。

Yuricon

1pass crf slow-firstpass + 文件输出
即能跑出个样品来看看效果(也能当备胎),还能得到更精准的码率和stats
然后2pass bitrate