[x264-devel] Re: Rate control in x264

[Loren Merritt]

On Tue, 22 May 2007, Son Minh Tran wrote:

> So in order to have the x264 encoder (as a whole encoding chain) independent 
> from the entropy coder, I have two choices to run x264 as followings:
> 1) ./x264 -b 4 -r 7 --mixed-refs -A all -8 -qp [0..32] -o <Output> 
> <Input.yuv> <width>x<length>
> 2) ./x264 -b 4 -r 7 --mixed-refs -A all -8 -crf [0.0 ... 1.0] -o <Output> 
> <Input.yuv> <width>x<length>
> I use also -r 7 (max reference frameNo) --mixed-ref (block 8x8 can use other 
> RefFrame than the neighbour block in the same MB) and -A all -8 (chack all 
> possible types of block) to maximize the advanced features of h264.

All good except the ranges of the options. -r goes up to 16, --qp and 
--crf go up to 51 (not that I'm necessarily suggesting to use the max 
values.)

> My question is still with the addition of  -qp N or -crf R  will I have the 
> independence between the entropy coder and the function units before it.

Yes.

> By defaut, qp is set to 26. Is it mean that I already have this 
> independence without explicitly specifying it at the command line.

Not anymore. Now there is no default ratecontrol mode, and you have to 
specify a qp or a crf or a bitrate, otherwise x264 will refuse to encode.

> The trellis setting (-t N) is disabled by defaut. How can I check wether the 
> rate distortion optimation is off? I think here you mentioned the proper 
> value of the option -m (with 7, x264 deploys the real RDO ). By defaut it 
> takes value 5, is it small enough?

Yes, the defaults for -m and -t are fine for your purpose.

--Loren Merritt

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