From 68b1edf19c441a59fd53c0286eee841244cf5f11 Mon Sep 17 00:00:00 2001
From: Paul B Mahol <onemda@gmail.com>
Date: Mon, 30 May 2022 11:36:22 +0200
Subject: [PATCH] avfilter: add virtualbass filter
Signed-off-by: Paul B Mahol <onemda@gmail.com>
---
doc/filters.texi | 20 ++++
libavfilter/Makefile | 1 +
libavfilter/af_virtualbass.c | 183 +++++++++++++++++++++++++++++++++++
libavfilter/allfilters.c | 1 +
4 files changed, 205 insertions(+)
create mode 100644 libavfilter/af_virtualbass.c
@@ -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.
@@ -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
new file mode 100644
@@ -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,
+};
@@ -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;
--
2.36.1