[Mp4-tech] H.264: about the caculation of mvCLX

[Alan Thomson]

Hi -
The equations are correct; the text is misleading.
Delete "multiplying", insert "dividing" and it makes more sense.
For example a luma component of 3 (quarter-luma-samples)
yields a chroma component of 3 (eighth-chroma-samples).
BR,
Alan
> -----Original Message-----
> From: AngelZhang innosis.com.cn [mailto:AngelZhang innosis.com.cn]
> Sent: 28 June 2023 02:47
> To: mp4-tech lists.mpegif.org
> Subject: [Mp4-tech] H.264: about the caculation of mvCLX
> 
> 
> hi experts,
>   In the part 8.4.1.4 of H264 standard,the description of mvCLX's
> derivation is written as following:
>   "if the current macroblock is a frame macroblock,the horizontal and
> vertical components of the chroma motion vector mvCLX are derived by
> multiplying the corresponding components of luma motion 
> vector mvLX by 2,
> through mapping one-quarter sample mvLX units to one-eighth 
> sample mvCLX
> units"
>   but the formular :
>     mvCLX[0]=mvLX[0]
>     mvCLX[1]=mvLX[1]
>   havn't implement what the standard has said to multiply 2.
> 
>   i am confused about it very much.please give me your idea.
> 
> thanks
> angel
> 
> 
> 
> 
> 
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