[Mp4-tech] Re: Regarding Luma16DC and Luma16AC

[Luca]

>  Hi all,
>
>  Currently I am trying to understand JM software for my project.
>
>  While doing so, I observed the following things.
>
>  1)
>
>  For some Macro blocks I am getting Luma, ChromaDc and ChromaAC coefficients.
>
>  For other Macro blocks, I am getting Luma16DC, Luma16AC and Chroma.
>
>  What is difference of these coefficients? And how to stop Luma16DC and
>  Luma16AC coefficients?

Luma16[A/D]C are the value of the transformed quantized residuals when
performing the intra prediction for the macroblock as a whole (16x16).
You have one block of 4x4 DC coefficients and 16 blocks containing the
AC coefficients. Otherwise, if predicting 4x4 sub-blocks, you have 16
blocks of 4x4 coefficients.
You find here an exhaustive explanation:
http://vcodex.com/files/h264_transform.pdf
If you want, you can disable the 16x16 Intra prediction.
>  2)
>
>  I am not getting all the 16, 4x4 blocks for my CAVLC (Depending on CBP value).
>
>  In this case, what values shall I take for nA and nB in the
>  calculation of nC in "TrailingOnes" and "Total Coeffs" in lookup
>  table.

If the CBP is signalizing that the four 4x4 blocks of an 8x8 block
have no non-zero residuals, than when using one of them to calculate
nC, you should consider nA (nB, respectively) equal to zero.