libavfilter: improve atempo audio quality

Reduce audio fragment alignment jitter by penalizing alignment
correction offsets that deviate too much from the target offset.
This is accomplished by multiplying the cross correlation search
window with a quadratic function.

Signed-off-by: Pavel Koshevoy <pavel@homestead.aragog.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

diff --git a/libavfilter/af_atempo.c b/libavfilter/af_atempo.c
index 1ccc3f56291fff876208cca3dbc7aac93e3c07a5..92390cf2176f75b66bc0aef19068633008c222f2 100644 (file)
--- a/libavfilter/af_atempo.c
+++ b/libavfilter/af_atempo.c
@@ -654,7 +654,7 @@ static int yae_align(AudioFragment *frag,
 
         // normalize:
         FFTSample drifti = (FFTSample)(drift + i);
-        metric *= drifti;
+        metric *= drifti * (FFTSample)(i - i0) * (FFTSample)(i1 - i);
 
         if (metric > best_metric) {
             best_metric = metric;