[Ffmpeg-devel] H264 decoder internals

Måns Rullgård mru
Sat Jun 18 16:26:14 CEST 2005

I'm messing around with the H.264 decoder, and I'm having some trouble
figuring out how the standard maps to the code.

Around section 8.5.10 in the H.264 spec, there are a number of
equations similar to 8-339:

  d_ij = (c_ij * LevelScale(qP % 6, i, j) + 2^(3-qP/6)) >> (4 - qP / 6)

I looks like the value of LevelScale() is precomputed for all
combinations in the dequant_coeff array.  What I'm having some trouble
with, is understanding where the final value of that equation is
calculated.  I suppose it's disguised in some clever optimization.
Could someone please explain what's going on?

M?ns Rullg?rd
mru at inprovide.com

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