[Libav-user] Help : YUV value for a macroblock in a yuv240p frame

NDJORE BORIS ndjoreboris at gmail.com
Tue Apr 9 16:43:34 EEST 2019

Le mar. 9 avr. 2019 à 15:31, Simon Brown <simon.k.brown at gmail.com> a écrit :

> On Tue, 9 Apr 2019 at 14:20, NDJORE BORIS <ndjoreboris at gmail.com> wrote:
>> Hello guys,
>> I try to find pixels value for a given macroblock in a frame.
>> What I did is the following :
>> //for all macroblock in this frame
>> for(int mby=0; y<mb_height;y++)
>> {
>>          for(int mbx=0; x<mb_width;x++)
>>          {
>>              int xy =  mby*mb_stride+mbx;
>>              //Now for this 16x16 macroblock
>>             for(int y=0; y<16;y++)
>>             {
>>                for(int x=0; x<16;x++)
>>                {
>>                  //All pixels YUV value for this macroblock
>>                  y = data[0][linesize[0]*y+x];
>>                  u = data[1][linesize[1]*(y/2)+x/2]
>>                  v = data[2][linesize[2]*(y/2)+x/2]
>>              }
>> }
>> //Let's in an other macroblock
>> }
>> }
>> The problem is that for all macroblocks, I have the same Y, u and v
>> value. That's is true because I only use the same width and height for
>> every macroblock.
>> My question is to know how can I put difference in the above code to find
>> pixels yuv value for each macroblock in this frame.
>> I need your help, please.
>> Regards
>> Without having understood your code fully, you have two loops around the
> outside, one for mby and one for mbx, yet they use y<mb_height and y++,
> x<mb_width and x++.  You then inside these loops have a loop for x and y
> also comparing x and y and incrementing x and y.  That can't be right!
> Your inner assignments should probably be:
> y = data[0][linesize[0]*(mby*16)*y+(mbx*16 +x)]
> etc.
> Regards,
> Simon

Thank you simon.

You probably right. The first loop is to obten all macroblock in the frame
and the second is to optain each pixel in the macroblock, I thinked.
But in what you gave if I do this for two different block, I think that I
will obtain the same value for "y".
Can you explain me  how can I do to obtain different "y" value for each
macroblock if I'm wrong , please?


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