[Ffmpeg-devel] [PATCH] flacenc - add basic stereo decorrelation

Justin Ruggles jruggle
Mon Jun 26 04:37:31 CEST 2006

Michael Niedermayer wrote:
> Hi
> On Sun, Jun 25, 2006 at 05:02:00PM -0400, Justin Ruggles wrote:
> [...]
>>The estimation method calculates the sum of squares for left, right,
>>mid, and side channels.  It uses the minimum of L+R, L+S, R+S, or M+S.
>>I am open to any suggestions for methods that might work better.
> maybe using the differences from the last values would be more
> accurate (lt = left_ch[i] - left_ch[i-1]; ...)

You're right. That does help quite a bit. It's like estimating with
order 1 instead of order 0. I tried using order 2 & got even better results.

> and i think though i might be wrong that the sum of absolute values will
> be a better choice then the sum of squares for estimating the number of
> bits which is after all what matters in the decission of the decorrelation
> method

After doing more testing, I found that sum of abs vs. sum of squares
didn't really make that much difference.  About 1/2 did a little better
& 1/2 did a little worse.  Absolute value is a simpler calculation, so
it gets my vote.

Here is another patch.


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