A couple of questions

[dakedk2]

So yeah right to the questions.
1. It seems that by default I can't change subme slider from x264, then how can I enable it?
2. Looks like there's new feature in x264 rate mode "Constant QP". is this some kind of CRF in handbrake/meGUI?
3. How to add subtitle built-in from my source video mkv container? should I demux it first and add it ?
Thanks!

[meRobs]

Q1: what do you mean by the 'subme slider' ?
As for question 3: read the Suibtitle Guide (viewtopic.php?f=17&t=10927), especially the last paragraph in Section 1.

[AnonCrow]

First , select Options -> User Interface mode -> Expert mode.

1. It seems that by default I can't change subme slider from x264, then how can I enable it?

Need to have 'custom' selected in the x264 preset selector. Even if you select a different subme value in the advanced settings.

You can use one of the x264 presets with a custom subme value, if you enter the command-line option at the bottom in advanced settings.

2. Looks like there's new feature in x264 rate mode "Constant QP". is this some kind of CRF in handbrake/meGUI?

It is what it says : the 1-pass constant quantizer encoding mode in x264 , which should almost never be used, --qp 0 being the rare exception.
For CRF, select the 'variable bitrate' option, then look for the actual crf value used in the command-line visible below in the video options tab.

[dakedk2]

@meRobs & AnonCrow: Well that explains a lot! thanks to both of you. Now I'm just asking your opinion. If I set my ref frame and b frame higher than my source will it be useless? I once have quite poor source with low bitrate & cheapo 15 fps. So I though I'd convert it cranking up bitrates and doubling fps and resulting output over 1 GB! And then I learnt it's highly inefficient in size & thought that output will never be better than source unless both are lossless. Now will that be the case with b frame & ref frame?

[meRobs]

Firstly, you can never create an output with better quality than the source.
Secondly, the optimum number of reference and B frames for a conversion is independent on what is in the source -- their number depends on the way the video encoder does its compression.

[AnonCrow]

More b-frames and reference frames never hurts the quality, but any more than 5-6 is usually
pointless because the improvements are negligible (less than one percent). [1]
If endoding anime (and thus using --tune animation), a few more are useful.

With b-adapt 2 , increased b-frames will slow down the encoding a lot.
Most hardware players have limitations on how many b and ref-frames they can handle,
DXVA accelerated playback on computer is limited on number of ref-frames [2]

Whenever you encode something into a lossy format, you will always lose some quality, no matter the settings,
doesn't matter if the source is lossy or a lossless original. Around CRF 18 will likely produce a result that is
transparent/indistinguishable from the original - at least if you don't freeze individual frames and zoom in.


[1] http://forum.doom9.org/showthread.php?t=144873 ,
[2] the last number on the right in the tables in http://en.wikipedia.org/wiki/H.264/MPEG-4_AVC#Levels