[Mp4-tech] H.264 doubts

[pavan kumar nittala]

  Hai Prabhakar
Assume QCIF in which we have the following data for Width and Height.
Width   =  176(pixels)
           =  11 (Macroblocks)			
           =  44(8x8 Blocks)
Height  =  144 (pixels)
           =    9 (MBs)
           =   36 (8x8 Blocks)	
Then img->mb_x represents macroblock position starting from zero ....
its maximum value can be 10.
img->mb_y represents MB position starting from zero ..
It can take a value of 8 maximum ...
img->block_x  Increments for 4 for every Macro block.
its maximum value can be 10x4 =40.
img->block_y Increments for 4 for every Macro block.
Its maximum value can be 8x4 =32.
img->pix_x  increments by 16 for every MB ... so it indicates the no of pixels upto the current mb_x ......
Its maximum value can be 10x16 =160.
similarly img->pix_y can take a max value of 8x16 =128 .
img->pix_c_x and pix_c_y  have the similar meanings ...
except they have to be multiplied by 8 ... because C stands for Chroma .... and  this is for YUV 420 format only ...
they can have max values of 10x 8 =80 and 8x8 =64 r'ly ....
Hope i have answered ur point
experts correct me if I am wrong anywhere ...
pavan 
On Thu, 24 Feb 2024 pasunuti prabhakar wrote :
>Hello Experts,
>
>       I am working on the JVT9.2 decoder. I have certain doubts in code..
>
>    What exactly the variables "block_x","block_y","pix_x","pix_y","pix_c_x","pix_c_y" represents. With respect to a frame, what exactly these variables  indicates.
>
>Thanks in advance.
>
>Regards
>Prabhakar
>
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