avfilter: add virtualbass filter

Changelog

@@ -20,6 +20,7 @@ version 5.1:
 - tiltshelf audio filter
 - QOI image format support
 - ffprobe -o option
+- virtualbass audio filter
 
 
 version 5.0:

doc/filters.texi

@@ -6927,6 +6927,26 @@ Depth of modulation as a percentage. Range is 0.0 - 1.0.
 Default value is 0.5.
 @end table
 
+@section virtualbass
+
+Apply audio Virtual Bass filter.
+
+This filter accepts stereo input and produce stereo with LFE (2.1) channels output.
+The newly produced LFE channel have enhanced virtual bass originally obtained from both stereo channels.
+This filter outputs front left and front right channels unchanged as available in stereo input.
+
+The filter accepts the following options:
+
+@table @option
+@item cutoff
+Set the virtual bass cutoff frequency. Default value is 250 Hz.
+Allowed range is from 100 to 500 Hz.
+
+@item strength
+Set the virtual bass strength. Allowed range is from 0.5 to 3.
+Default value is 3.
+@end table
+
 @section volume
 
 Adjust the input audio volume.

libavfilter/Makefile

@@ -164,6 +164,7 @@ 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
+OBJS-$(CONFIG_VIRTUALBASS_FILTER)            += af_virtualbass.o
 OBJS-$(CONFIG_VOLUME_FILTER)                 += af_volume.o
 OBJS-$(CONFIG_VOLUMEDETECT_FILTER)           += af_volumedetect.o
 

libavfilter/af_virtualbass.c

@@ -0,0 +1,183 @@
+/*
+ * Copyright (c) 2022 Paul B Mahol
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg 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.
+ *
+ * FFmpeg 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 FFmpeg; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "libavutil/channel_layout.h"
+#include "libavutil/opt.h"
+#include "audio.h"
+#include "avfilter.h"
+#include "filters.h"
+#include "internal.h"
+
+#include <float.h>
+
+typedef struct AudioVirtualBassContext {
+    const AVClass *class;
+
+    double cutoff;
+    double strength;
+
+    double a[3], m[3], cf[2];
+} AudioVirtualBassContext;
+
+#define OFFSET(x) offsetof(AudioVirtualBassContext, x)
+#define TFLAGS AV_OPT_FLAG_AUDIO_PARAM | AV_OPT_FLAG_FILTERING_PARAM | AV_OPT_FLAG_RUNTIME_PARAM
+#define FLAGS AV_OPT_FLAG_AUDIO_PARAM | AV_OPT_FLAG_FILTERING_PARAM
+
+static const AVOption virtualbass_options[] = {
+    { "cutoff",   "set virtual bass cutoff",   OFFSET(cutoff),   AV_OPT_TYPE_DOUBLE, {.dbl=250},100,500, FLAGS },
+    { "strength", "set virtual bass strength", OFFSET(strength), AV_OPT_TYPE_DOUBLE, {.dbl=3},  0.5,  3, TFLAGS },
+    {NULL}
+};
+
+AVFILTER_DEFINE_CLASS(virtualbass);
+
+static int query_formats(AVFilterContext *ctx)
+{
+    AVFilterChannelLayouts *in_layout = NULL, *out_layout = NULL;
+    AVFilterFormats *formats = NULL;
+    int ret;
+
+    if ((ret = ff_add_format                 (&formats, AV_SAMPLE_FMT_DBLP )) < 0 ||
+        (ret = ff_set_common_formats         (ctx,      formats            )) < 0 ||
+        (ret = ff_add_channel_layout         (&in_layout, &(AVChannelLayout)AV_CHANNEL_LAYOUT_STEREO)) < 0 ||
+        (ret = ff_channel_layouts_ref(in_layout, &ctx->inputs[0]->outcfg.channel_layouts)) < 0 ||
+        (ret = ff_add_channel_layout         (&out_layout, &(AVChannelLayout)AV_CHANNEL_LAYOUT_2POINT1)) < 0 ||
+        (ret = ff_channel_layouts_ref(out_layout, &ctx->outputs[0]->incfg.channel_layouts)) < 0)
+        return ret;
+
+    return ff_set_common_all_samplerates(ctx);
+}
+
+static int config_input(AVFilterLink *inlink)
+{
+    AVFilterContext *ctx = inlink->dst;
+    AudioVirtualBassContext *s = ctx->priv;
+    const double Q = 0.707;
+    double g, k;
+
+    g = tan(M_PI * s->cutoff / inlink->sample_rate);
+    k = 1. / Q;
+    s->a[0] = 1. / (1. + g * (g + k));
+    s->a[1] = g * s->a[0];
+    s->a[2] = g * s->a[1];
+    s->m[0] = 0.;
+    s->m[1] = 0.;
+    s->m[2] = 1.;
+
+    return 0;
+}
+
+#define SQR(x) ((x) * (x))
+
+static double vb_fun(double x)
+{
+    double y = 2.5 * atan(0.9 * x) + 2.5 * sqrt(1. - SQR(0.9 * x)) - 2.5;
+
+    return y < 0. ? sin(y) : y;
+}
+
+static void vb_stereo(AVFilterContext *ctx, AVFrame *out, AVFrame *in)
+{
+    AudioVirtualBassContext *s = ctx->priv;
+    const double *lsrc = (const double *)in->extended_data[0];
+    const double *rsrc = (const double *)in->extended_data[1];
+    double *ldst = (double *)out->extended_data[0];
+    double *rdst = (double *)out->extended_data[1];
+    double *lfe = (double *)out->extended_data[2];
+    const double st = M_PI / s->strength;
+    const double a0 = s->a[0];
+    const double a1 = s->a[1];
+    const double a2 = s->a[2];
+    const double m0 = s->m[0];
+    const double m1 = s->m[1];
+    const double m2 = s->m[2];
+    double b0 = s->cf[0];
+    double b1 = s->cf[1];
+
+    memcpy(ldst, lsrc, in->nb_samples * sizeof(double));
+    memcpy(rdst, rsrc, in->nb_samples * sizeof(double));
+
+    for (int n = 0; n < in->nb_samples; n++) {
+        const double center = (lsrc[n] + rsrc[n]) * 0.5;
+        const double v0 = center;
+        const double v3 = v0 - b1;
+        const double v1 = a0 * b0 + a1 * v3;
+        const double v2 = b1 + a1 * b0 + a2 * v3;
+        double b, vb;
+
+        b0 = 2. * v1 - b0;
+        b1 = 2. * v2 - b1;
+
+        b = m0 * v0 + m1 * v1 + m2 * v2;
+        vb = sin(vb_fun(b) * st);
+
+        lfe[n] = vb;
+    }
+
+    s->cf[0] = b0;
+    s->cf[1] = b1;
+}
+
+static int filter_frame(AVFilterLink *inlink, AVFrame *in)
+{
+    AVFilterContext *ctx = inlink->dst;
+    AVFilterLink *outlink = ctx->outputs[0];
+    AVFrame *out;
+
+    out = ff_get_audio_buffer(outlink, in->nb_samples);
+    if (!out) {
+        av_frame_free(&in);
+        return AVERROR(ENOMEM);
+    }
+
+    vb_stereo(ctx, out, in);
+
+    out->pts = in->pts;
+    av_frame_free(&in);
+    return ff_filter_frame(outlink, out);
+}
+
+static const AVFilterPad inputs[] = {
+    {
+        .name         = "default",
+        .type         = AVMEDIA_TYPE_AUDIO,
+        .filter_frame = filter_frame,
+        .config_props = config_input,
+    },
+};
+
+static const AVFilterPad outputs[] = {
+    {
+        .name = "default",
+        .type = AVMEDIA_TYPE_AUDIO,
+    },
+};
+
+const AVFilter ff_af_virtualbass = {
+    .name            = "virtualbass",
+    .description     = NULL_IF_CONFIG_SMALL("Audio Virtual Bass."),
+    .priv_size       = sizeof(AudioVirtualBassContext),
+    .priv_class      = &virtualbass_class,
+    FILTER_INPUTS(inputs),
+    FILTER_OUTPUTS(outputs),
+    FILTER_QUERY_FUNC(query_formats),
+    .flags           = AVFILTER_FLAG_SUPPORT_TIMELINE_INTERNAL,
+    .process_command = ff_filter_process_command,
+};

libavfilter/allfilters.c

@@ -153,6 +153,7 @@ extern const AVFilter ff_af_tiltshelf;
 extern const AVFilter ff_af_treble;
 extern const AVFilter ff_af_tremolo;
 extern const AVFilter ff_af_vibrato;
+extern const AVFilter ff_af_virtualbass;
 extern const AVFilter ff_af_volume;
 extern const AVFilter ff_af_volumedetect;
 

libavfilter/version.h

@@ -31,7 +31,7 @@
 
 #include "version_major.h"
 
-#define LIBAVFILTER_VERSION_MINOR  40
+#define LIBAVFILTER_VERSION_MINOR  41
 #define LIBAVFILTER_VERSION_MICRO 100