avfilter: add audio surround upmixer

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

Changelog

@@ -16,6 +16,7 @@ version <next>:
 - spec compliant VP9 muxing support in MP4
 - remove the libnut muxer/demuxer wrappers
 - remove the libschroedinger encoder/decoder wrappers
+- surround audio filter
 
 version 3.3:
 - CrystalHD decoder moved to new decode API

doc/filters.texi

@@ -3792,6 +3792,36 @@ channels. Default is 0.3.
 Set level of input signal of original channel. Default is 0.8.
 @end table
 
+@section surround
+Apply audio surround upmix filter.
+
+This filter allows to produce multichannel output from stereo audio stream.
+
+The filter accepts the following options:
+
+@table @option
+@item chl_out
+Set output channel layout. By default, this is @var{5.1}.
+
+See @ref{channel layout syntax,,the Channel Layout section in the ffmpeg-utils(1) manual,ffmpeg-utils}
+for the required syntax.
+
+@item level_in
+Set input volume level. By default, this is @var{1}.
+
+@item level_out
+Set output volume level. By default, this is @var{1}.
+
+@item lfe
+Enable LFE channel output if output channel layout has it. By default, this is enabled.
+
+@item lfe_low
+Set LFE low cut off frequency. By default, this is @var{128} Hz.
+
+@item lfe_high
+Set LFE high cut off frequency. By default, this is @var{256} Hz.
+@end table
+
 @section treble
 
 Boost or cut treble (upper) frequencies of the audio using a two-pole

libavfilter/Makefile

@@ -108,6 +108,7 @@ OBJS-$(CONFIG_SILENCEREMOVE_FILTER)          += af_silenceremove.o
 OBJS-$(CONFIG_SOFALIZER_FILTER)              += af_sofalizer.o
 OBJS-$(CONFIG_STEREOTOOLS_FILTER)            += af_stereotools.o
 OBJS-$(CONFIG_STEREOWIDEN_FILTER)            += af_stereowiden.o
+OBJS-$(CONFIG_SURROUND_FILTER)               += af_surround.o
 OBJS-$(CONFIG_TREBLE_FILTER)                 += af_biquads.o
 OBJS-$(CONFIG_TREMOLO_FILTER)                += af_tremolo.o
 OBJS-$(CONFIG_VIBRATO_FILTER)                += af_vibrato.o generate_wave_table.o

libavfilter/allfilters.c

@@ -121,6 +121,7 @@ static void register_all(void)
     REGISTER_FILTER(SOFALIZER,      sofalizer,      af);
     REGISTER_FILTER(STEREOTOOLS,    stereotools,    af);
     REGISTER_FILTER(STEREOWIDEN,    stereowiden,    af);
+    REGISTER_FILTER(SURROUND,       surround,       af);
     REGISTER_FILTER(TREBLE,         treble,         af);
     REGISTER_FILTER(TREMOLO,        tremolo,        af);
     REGISTER_FILTER(VIBRATO,        vibrato,        af);

libavfilter/version.h

@@ -30,7 +30,7 @@
 #include "libavutil/version.h"
 
 #define LIBAVFILTER_VERSION_MAJOR   6
-#define LIBAVFILTER_VERSION_MINOR  90
+#define LIBAVFILTER_VERSION_MINOR  91
 #define LIBAVFILTER_VERSION_MICRO 100
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \