[Ffmpeg-devel] [PATCH][RFC] ac3enc window generation

Benjamin Larsson banan
Thu Apr 20 16:54:34 CEST 2006


The following patch generates the ac3 window used by the ac3 encoder.
The patch is based on code posted by Justin Ruggles. This also gives the
opportunity to use a diffrent rounding for the mdct window
(truncating/rounding/whatever, truncation is used now). The attached
octave script gives the following values for me:

max_rounderror =  3.8178e-05
max_floorerror =  7.3856e-05
round_bits = 14.677
floor_bits = 13.725
roundsse =  7.3792e-08
floorsse =  4.6057e-07

>From these values one can see that rounding gives lower error on
average. But from the resulting plot one can see that truncation results
in the gain to always be under 1 while rounding results in the gain to
be centered around 1. So with rounding one would get a (very) slightly
lower error but the window gain could overflow the result in (very)
extream situations.

So, apply with/without rounding or patch rejected.

MvH
Benjamin Larsson

-- 
"incorrect information" is an oxymoron. Information is, by definition, factual, correct.

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