[x264-devel] Re: Rate control in x264

[Son Minh Tran]

Dear Loren Merritt
thank you again for your prompt answer. You wrote that from now on we 
have to specify qp or crf or bitrate explicitly. It is from which 
revision? I checked out the one on April 3rd 07, and I can run without 
these options. Anyway can you give me a hint into the sourcecode to 
verify  directly  that  a constant  Q  is used and  RDO / trellis is off.
Thank you very much
Son
 
Loren Merritt a écrit :
> 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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