avfilter: add axcorrelate filter

Changelog

@@ -24,6 +24,7 @@ version <next>:
 - AV1 encoding support via librav1e
 - AV1 frame merge bitstream filter
 - AV1 Annex B demuxer
+- axcorrelate filter
 
 
 version 4.2:

doc/filters.texi

@@ -2531,6 +2531,39 @@ ffmpeg -i INPUT -af atrim=end_sample=1000
 
 @end itemize
 
+@section axcorrelate
+Calculate normalized cross-correlation between two input audio streams.
+
+Resulted samples are always between -1 and 1 inclusive.
+If result is 1 it means two input samples are highly correlated in that selected segment.
+Result 0 means they are not correlated at all.
+If result is -1 it means two input samples are out of phase, which means they cancel each
+other.
+
+The filter accepts the following options:
+
+@table @option
+@item size
+Set size of segment over which cross-correlation is calculated.
+Default is 256. Allowed range is from 2 to 131072.
+
+@item algo
+Set algorithm for cross-correlation. Can be @code{slow} or @code{fast}.
+Default is @code{slow}. Fast algorithm assumes mean values over any given segment
+are always zero and thus need much less calculations to make.
+This is generally not true, but is valid for typical audio streams.
+@end table
+
+@subsection Examples
+
+@itemize
+@item
+Calculate correlation between channels in stereo audio stream:
+@example
+ffmpeg -i stereo.wav -af channelsplit,axcorrelate=size=1024:algo=fast correlation.wav
+@end example
+@end itemize
+
 @section bandpass
 
 Apply a two-pole Butterworth band-pass filter with central

libavfilter/Makefile

@@ -88,6 +88,7 @@ OBJS-$(CONFIG_ASTATS_FILTER)                 += af_astats.o
 OBJS-$(CONFIG_ASTREAMSELECT_FILTER)          += f_streamselect.o framesync.o
 OBJS-$(CONFIG_ATEMPO_FILTER)                 += af_atempo.o
 OBJS-$(CONFIG_ATRIM_FILTER)                  += trim.o
+OBJS-$(CONFIG_AXCORRELATE_FILTER)            += af_axcorrelate.o
 OBJS-$(CONFIG_AZMQ_FILTER)                   += f_zmq.o
 OBJS-$(CONFIG_BANDPASS_FILTER)               += af_biquads.o
 OBJS-$(CONFIG_BANDREJECT_FILTER)             += af_biquads.o

libavfilter/allfilters.c

@@ -81,6 +81,7 @@ extern AVFilter ff_af_astats;
 extern AVFilter ff_af_astreamselect;
 extern AVFilter ff_af_atempo;
 extern AVFilter ff_af_atrim;
+extern AVFilter ff_af_axcorrelate;
 extern AVFilter ff_af_azmq;
 extern AVFilter ff_af_bandpass;
 extern AVFilter ff_af_bandreject;

libavfilter/version.h

@@ -30,7 +30,7 @@
 #include "libavutil/version.h"
 
 #define LIBAVFILTER_VERSION_MAJOR   7
-#define LIBAVFILTER_VERSION_MINOR  66
+#define LIBAVFILTER_VERSION_MINOR  67
 #define LIBAVFILTER_VERSION_MICRO 100