avfilter: add arbitrary audio IIR filter

Signed-off-by: Paul B Mahol <onemda@gmail.com>

Changelog

@@ -33,6 +33,7 @@ version <next>:
 - deconvolve video filter
 - entropy video filter
 - hilbert audio filter source
+- aiir audio filter
 
 
 version 3.4:

doc/filters.texi

@@ -1060,6 +1060,41 @@ the reduction.
 Default is @code{average}. Can be @code{average} or @code{maximum}.
 @end table
 
+@section aiir
+
+Apply an arbitrary Infinite Impulse Response filter.
+
+It accepts the following parameters:
+
+@table @option
+@item a
+Set denominator/poles coefficients.
+
+@item b
+Set nominator/zeros coefficients.
+
+@item dry_gain
+Set input gain.
+
+@item wet_gain
+Set output gain.
+@end table
+
+Coefficients are separated by spaces and are in ascending order.
+Different coefficients can be provided for every channel, in such case
+use '|' to separate coefficients. Last provided coefficients will be
+used for all remaining channels.
+
+@subsection Examples
+
+@itemize
+@item
+Apply 2 pole elliptic notch at arround 5000Hz for 48000 Hz sample rate:
+@example
+aiir=b=7.957584807809675810E-1 -2.575128568908332300 3.674839853930788710 -2.57512875289799137 7.957586296317130880E-1:a=1 -2.86950072432325953 3.63022088054647218 -2.28075678147272232 6.361362326477423500E-1
+@end example
+@end itemize
+
 @section alimiter
 
 The limiter prevents an input signal from rising over a desired threshold.

libavfilter/Makefile

@@ -43,6 +43,7 @@ OBJS-$(CONFIG_AFFTFILT_FILTER)               += af_afftfilt.o
 OBJS-$(CONFIG_AFIR_FILTER)                   += af_afir.o
 OBJS-$(CONFIG_AFORMAT_FILTER)                += af_aformat.o
 OBJS-$(CONFIG_AGATE_FILTER)                  += af_agate.o
+OBJS-$(CONFIG_AIIR_FILTER)                   += af_aiir.o
 OBJS-$(CONFIG_AINTERLEAVE_FILTER)            += f_interleave.o
 OBJS-$(CONFIG_ALIMITER_FILTER)               += af_alimiter.o
 OBJS-$(CONFIG_ALLPASS_FILTER)                += af_biquads.o

libavfilter/af_biquads.c

@@ -375,6 +375,8 @@ static int config_filter(AVFilterLink *outlink, int reset)
         av_assert0(0);
     }
 
+    av_log(ctx, AV_LOG_VERBOSE, "a=%lf %lf %lf:b=%lf %lf %lf\n", s->a0, s->a1, s->a2, s->b0, s->b1, s->b2);
+
     s->a1 /= s->a0;
     s->a2 /= s->a0;
     s->b0 /= s->a0;

libavfilter/allfilters.c

@@ -54,6 +54,7 @@ static void register_all(void)
     REGISTER_FILTER(AFIR,           afir,           af);
     REGISTER_FILTER(AFORMAT,        aformat,        af);
     REGISTER_FILTER(AGATE,          agate,          af);
+    REGISTER_FILTER(AIIR,           aiir,           af);
     REGISTER_FILTER(AINTERLEAVE,    ainterleave,    af);
     REGISTER_FILTER(ALIMITER,       alimiter,       af);
     REGISTER_FILTER(ALLPASS,        allpass,        af);

libavfilter/version.h

@@ -30,7 +30,7 @@
 #include "libavutil/version.h"
 
 #define LIBAVFILTER_VERSION_MAJOR   7
-#define LIBAVFILTER_VERSION_MINOR  10
+#define LIBAVFILTER_VERSION_MINOR  11
 #define LIBAVFILTER_VERSION_MICRO 100
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \