avfilter: add audio crossfeed filter

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

Changelog

@@ -12,6 +12,7 @@ version <next>:
 - afir audio filter
 - scale_cuda CUDA based video scale filter
 - librsvg support for svg rasterization
+- crossfeed audio filter
 
 version 3.3:
 - CrystalHD decoder moved to new decode API

doc/filters.texi

@@ -2251,6 +2251,35 @@ Set temperature degree in Celsius. This is the temperature of the environment.
 Default is 20.
 @end table
 
+@section crossfeed
+Apply headphone crossfeed filter.
+
+Crossfeed is the process of blending the left and right channels of stereo
+audio recording.
+It is mainly used to reduce extreme stereo separation of low frequencies.
+
+The intent is to produce more speaker like sound to the listener.
+
+The filter accepts the following options:
+
+@table @option
+@item strength
+Set strength of crossfeed. Default is 0.2. Allowed range is from 0 to 1.
+This sets gain of low shelf filter for side part of stereo image.
+Default is -6dB. Max allowed is -30db when strength is set to 1.
+
+@item range
+Set soundstage wideness. Default is 0.5. Allowed range is from 0 to 1.
+This sets cut off frequency of low shelf filter. Default is cut off near
+1550 Hz. With range set to 1 cut off frequency is set to 2100 Hz.
+
+@item level_in
+Set input gain. Default is 0.9.
+
+@item level_out
+Set output gain. Default is 1.
+@end table
+
 @section crystalizer
 Simple algorithm to expand audio dynamic range.
 

libavfilter/Makefile

@@ -81,6 +81,7 @@ OBJS-$(CONFIG_CHANNELSPLIT_FILTER)           += af_channelsplit.o
 OBJS-$(CONFIG_CHORUS_FILTER)                 += af_chorus.o generate_wave_table.o
 OBJS-$(CONFIG_COMPAND_FILTER)                += af_compand.o
 OBJS-$(CONFIG_COMPENSATIONDELAY_FILTER)      += af_compensationdelay.o
+OBJS-$(CONFIG_CROSSFEED_FILTER)              += af_crossfeed.o
 OBJS-$(CONFIG_CRYSTALIZER_FILTER)            += af_crystalizer.o
 OBJS-$(CONFIG_DCSHIFT_FILTER)                += af_dcshift.o
 OBJS-$(CONFIG_DYNAUDNORM_FILTER)             += af_dynaudnorm.o

libavfilter/af_crossfeed.c

+/*
+ * 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 "avfilter.h"
+#include "audio.h"
+#include "formats.h"
+
+typedef struct CrossfeedContext {
+    const AVClass *class;
+
+    double range;
+    double strength;
+    double level_in;
+    double level_out;
+
+    double a0, a1, a2;
+    double b0, b1, b2;
+
+    double i1, i2;
+    double o1, o2;
+} CrossfeedContext;
+
+static int query_formats(AVFilterContext *ctx)
+{
+    AVFilterFormats *formats = NULL;
+    AVFilterChannelLayouts *layout = NULL;
+    int ret;
+
+    if ((ret = ff_add_format                 (&formats, AV_SAMPLE_FMT_DBL  )) < 0 ||
+        (ret = ff_set_common_formats         (ctx     , formats            )) < 0 ||
+        (ret = ff_add_channel_layout         (&layout , AV_CH_LAYOUT_STEREO)) < 0 ||
+        (ret = ff_set_common_channel_layouts (ctx     , layout             )) < 0 ||
+        (ret = ff_set_common_samplerates     (ctx     , ff_all_samplerates())) < 0)
+        return ret;
+
+    return 0;
+}
+
+static int config_input(AVFilterLink *inlink)
+{
+    AVFilterContext *ctx = inlink->dst;
+    CrossfeedContext *s = ctx->priv;
+    double A = exp(s->strength * -30 / 40 * log(10.));
+    double w0 = 2 * M_PI * (1. - s->range) * 2100 / inlink->sample_rate;
+    double alpha;
+
+    alpha = sin(w0) / 2 * sqrt(2 * (1 / 0.5 - 1) + 2);
+
+    s->a0 =          (A + 1) + (A - 1) * cos(w0) + 2 * sqrt(A) * alpha;
+    s->a1 =    -2 * ((A - 1) + (A + 1) * cos(w0));
+    s->a2 =          (A + 1) + (A - 1) * cos(w0) - 2 * sqrt(A) * alpha;
+    s->b0 =     A * ((A + 1) - (A - 1) * cos(w0) + 2 * sqrt(A) * alpha);
+    s->b1 = 2 * A * ((A - 1) - (A + 1) * cos(w0));
+    s->b2 =     A * ((A + 1) - (A - 1) * cos(w0) - 2 * sqrt(A) * alpha);
+
+    s->a1 /= s->a0;
+    s->a2 /= s->a0;
+    s->b0 /= s->a0;
+    s->b1 /= s->a0;
+    s->b2 /= s->a0;
+
+    return 0;
+}
+
+static int filter_frame(AVFilterLink *inlink, AVFrame *in)
+{
+    AVFilterContext *ctx = inlink->dst;
+    AVFilterLink *outlink = ctx->outputs[0];
+    CrossfeedContext *s = ctx->priv;
+    const double *src = (const double *)in->data[0];
+    const double level_in = s->level_in;
+    const double level_out = s->level_out;
+    const double b0 = s->b0;
+    const double b1 = s->b1;
+    const double b2 = s->b2;
+    const double a1 = s->a1;
+    const double a2 = s->a2;
+    AVFrame *out;
+    double *dst;
+    int n;
+
+    if (av_frame_is_writable(in)) {
+        out = in;
+    } else {
+        out = ff_get_audio_buffer(inlink, in->nb_samples);
+        if (!out) {
+            av_frame_free(&in);
+            return AVERROR(ENOMEM);
+        }
+        av_frame_copy_props(out, in);
+    }
+    dst = (double *)out->data[0];
+
+    for (n = 0; n < out->nb_samples; n++, src += 2, dst += 2) {
+        double mid = (src[0] + src[1]) * level_in * .5;
+        double side = (src[0] - src[1]) * level_in * .5;
+        double oside = side * b0 + s->i1 * b1 + s->i2 * b2 - s->o1 * a1 - s->o2 * a2;
+
+        s->i2 = s->i1;
+        s->i1 = side;
+        s->o2 = s->o1;
+        s->o1 = oside;
+
+        dst[0] = (mid + oside) * level_out;
+        dst[1] = (mid - oside) * level_out;
+    }
+
+    if (out != in)
+        av_frame_free(&in);
+    return ff_filter_frame(outlink, out);
+}
+
+#define OFFSET(x) offsetof(CrossfeedContext, x)
+#define FLAGS AV_OPT_FLAG_AUDIO_PARAM|AV_OPT_FLAG_FILTERING_PARAM
+
+static const AVOption crossfeed_options[] = {
+    { "strength",  "set crossfeed strength",  OFFSET(strength),  AV_OPT_TYPE_DOUBLE, {.dbl=.2}, 0, 1, FLAGS },
+    { "range",     "set soundstage wideness", OFFSET(range),     AV_OPT_TYPE_DOUBLE, {.dbl=.5}, 0, 1, FLAGS },
+    { "level_in",  "set level in",            OFFSET(level_in),  AV_OPT_TYPE_DOUBLE, {.dbl=.9}, 0, 1, FLAGS },
+    { "level_out", "set level out",           OFFSET(level_out), AV_OPT_TYPE_DOUBLE, {.dbl=1.}, 0, 1, FLAGS },
+    { NULL }
+};
+
+AVFILTER_DEFINE_CLASS(crossfeed);
+
+static const AVFilterPad inputs[] = {
+    {
+        .name         = "default",
+        .type         = AVMEDIA_TYPE_AUDIO,
+        .filter_frame = filter_frame,
+        .config_props = config_input,
+    },
+    { NULL }
+};
+
+static const AVFilterPad outputs[] = {
+    {
+        .name = "default",
+        .type = AVMEDIA_TYPE_AUDIO,
+    },
+    { NULL }
+};
+
+AVFilter ff_af_crossfeed = {
+    .name           = "crossfeed",
+    .description    = NULL_IF_CONFIG_SMALL("Apply headphone crossfeed filter."),
+    .query_formats  = query_formats,
+    .priv_size      = sizeof(CrossfeedContext),
+    .priv_class     = &crossfeed_class,
+    .inputs         = inputs,
+    .outputs        = outputs,
+};

libavfilter/allfilters.c

@@ -94,6 +94,7 @@ static void register_all(void)
     REGISTER_FILTER(CHORUS,         chorus,         af);
     REGISTER_FILTER(COMPAND,        compand,        af);
     REGISTER_FILTER(COMPENSATIONDELAY, compensationdelay, af);
+    REGISTER_FILTER(CROSSFEED,      crossfeed,      af);
     REGISTER_FILTER(CRYSTALIZER,    crystalizer,    af);
     REGISTER_FILTER(DCSHIFT,        dcshift,        af);
     REGISTER_FILTER(DYNAUDNORM,     dynaudnorm,     af);

libavfilter/version.h

@@ -30,8 +30,8 @@
 #include "libavutil/version.h"
 
 #define LIBAVFILTER_VERSION_MAJOR   6
-#define LIBAVFILTER_VERSION_MINOR  89
-#define LIBAVFILTER_VERSION_MICRO 101
+#define LIBAVFILTER_VERSION_MINOR  90
+#define LIBAVFILTER_VERSION_MICRO 100
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \
                                                LIBAVFILTER_VERSION_MINOR, \