lavfi: add volume filter

Based on the volume filter in FFmpeg written by Stefano Sabatini
<stefasab@gmail.com>.

Changelog

@@ -4,6 +4,7 @@ releases are sorted from youngest to oldest.
 version <next>:
 - ashowinfo audio filter
 - 24-bit FLAC encoding
+- audio volume filter
 
 
 version 9_beta2:

doc/filters.texi

@@ -359,6 +359,59 @@ not meant to be used directly, it is inserted automatically by libavfilter
 whenever conversion is needed. Use the @var{aformat} filter to force a specific
 conversion.
 
+@section volume
+
+Adjust the input audio volume.
+
+The filter accepts the following named parameters:
+@table @option
+
+@item volume
+Expresses how the audio volume will be increased or decreased.
+
+Output values are clipped to the maximum value.
+
+The output audio volume is given by the relation:
+@example
+@var{output_volume} = @var{volume} * @var{input_volume}
+@end example
+
+Default value for @var{volume} is 1.0.
+
+@item precision
+Mathematical precision.
+
+This determines which input sample formats will be allowed, which affects the
+precision of the volume scaling.
+
+@table @option
+@item fixed
+8-bit fixed-point; limits input sample format to U8, S16, and S32.
+@item float
+32-bit floating-point; limits input sample format to FLT. (default)
+@item double
+64-bit floating-point; limits input sample format to DBL.
+@end table
+@end table
+
+@subsection Examples
+
+@itemize
+@item
+Halve the input audio volume:
+@example
+volume=volume=0.5
+volume=volume=1/2
+volume=volume=-6.0206dB
+@end example
+
+@item
+Increase input audio power by 6 decibels using fixed-point precision:
+@example
+volume=volume=6dB:precision=fixed
+@end example
+@end itemize
+
 @c man end AUDIO FILTERS
 
 @chapter Audio Sources

libavfilter/Makefile

@@ -35,6 +35,7 @@ OBJS-$(CONFIG_CHANNELMAP_FILTER)             += af_channelmap.o
 OBJS-$(CONFIG_CHANNELSPLIT_FILTER)           += af_channelsplit.o
 OBJS-$(CONFIG_JOIN_FILTER)                   += af_join.o
 OBJS-$(CONFIG_RESAMPLE_FILTER)               += af_resample.o
+OBJS-$(CONFIG_VOLUME_FILTER)                 += af_volume.o
 
 OBJS-$(CONFIG_ANULLSRC_FILTER)               += asrc_anullsrc.o
 

libavfilter/af_volume.h

+/*
+ * This file is part of Libav.
+ *
+ * Libav is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * Libav is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with Libav; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file
+ * audio volume filter
+ */
+
+#ifndef AVFILTER_AF_VOLUME_H
+#define AVFILTER_AF_VOLUME_H
+
+#include "libavutil/common.h"
+#include "libavutil/float_dsp.h"
+#include "libavutil/opt.h"
+#include "libavutil/samplefmt.h"
+
+enum PrecisionType {
+    PRECISION_FIXED = 0,
+    PRECISION_FLOAT,
+    PRECISION_DOUBLE,
+};
+
+typedef struct VolumeContext {
+    const AVClass *class;
+    AVFloatDSPContext fdsp;
+    enum PrecisionType precision;
+    double volume;
+    int    volume_i;
+    int    channels;
+    int    planes;
+    enum AVSampleFormat sample_fmt;
+
+    void (*scale_samples)(uint8_t *dst, const uint8_t *src, int nb_samples,
+                          int volume);
+    int samples_align;
+} VolumeContext;
+
+#endif /* AVFILTER_AF_VOLUME_H */

libavfilter/allfilters.c

@@ -46,6 +46,7 @@ void avfilter_register_all(void)
     REGISTER_FILTER (CHANNELSPLIT,channelsplit,af);
     REGISTER_FILTER (JOIN,        join,        af);
     REGISTER_FILTER (RESAMPLE,    resample,    af);
+    REGISTER_FILTER (VOLUME,      volume,      af);
 
     REGISTER_FILTER (ANULLSRC,    anullsrc,    asrc);
 

libavfilter/version.h

@@ -29,7 +29,7 @@
 #include "libavutil/avutil.h"
 
 #define LIBAVFILTER_VERSION_MAJOR  3
-#define LIBAVFILTER_VERSION_MINOR  2
+#define LIBAVFILTER_VERSION_MINOR  3
 #define LIBAVFILTER_VERSION_MICRO  0
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \