avfilter: add stereowiden filter

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

Changelog

@@ -6,6 +6,7 @@ version <next>:
 - extrastereo filter
 - ocr filter
 - alimiter filter
+- stereowiden filter
 
 
 version 2.8:

doc/filters.texi

@@ -2394,6 +2394,33 @@ silenceremove=1:5:0.02
 @end example
 @end itemize
 
+@section stereowiden
+
+This filter enhance the stereo effect by suppressing signal common to both
+channels and by delaying the signal of left into right and vice versa,
+thereby widening the stereo effect.
+
+The filter accepts the following options:
+
+@table @option
+@item delay
+Time in milliseconds of the delay of left signal into right and vice versa.
+Default is 20 milliseconds.
+
+@item feedback
+Amount of gain in delayed signal into right and vice versa. Gives a delay
+effect of left signal in right output and vice versa which gives widening
+effect. Default is 0.3.
+
+@item crossfeed
+Cross feed of left into right with inverted phase. This helps in suppressing
+the mono. If the value is 1 it will cancel all the signal common to both
+channels. Default is 0.3.
+
+@item drymix
+Set level of input signal of original channel. Default is 0.8.
+@end table
+
 @section treble
 
 Boost or cut treble (upper) frequencies of the audio using a two-pole

libavfilter/Makefile

@@ -80,6 +80,7 @@ OBJS-$(CONFIG_RESAMPLE_FILTER)               += af_resample.o
 OBJS-$(CONFIG_SIDECHAINCOMPRESS_FILTER)      += af_sidechaincompress.o
 OBJS-$(CONFIG_SILENCEDETECT_FILTER)          += af_silencedetect.o
 OBJS-$(CONFIG_SILENCEREMOVE_FILTER)          += af_silenceremove.o
+OBJS-$(CONFIG_STEREOWIDEN_FILTER)            += af_stereowiden.o
 OBJS-$(CONFIG_TREBLE_FILTER)                 += af_biquads.o
 OBJS-$(CONFIG_VOLUME_FILTER)                 += af_volume.o
 OBJS-$(CONFIG_VOLUMEDETECT_FILTER)           += af_volumedetect.o

libavfilter/af_stereowiden.c

+/*
+ * Copyright (C) 2012 VLC authors and VideoLAN
+ * Author : Sukrit Sangwan < sukritsangwan at gmail dot com >
+ *
+ * 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 StereoWidenContext {
+    const AVClass *class;
+
+    float delay;
+    float feedback;
+    float crossfeed;
+    float drymix;
+
+    float *buffer;
+    float *write;
+    int length;
+} StereoWidenContext;
+
+#define OFFSET(x) offsetof(StereoWidenContext, x)
+#define A AV_OPT_FLAG_AUDIO_PARAM|AV_OPT_FLAG_FILTERING_PARAM
+
+static const AVOption stereowiden_options[] = {
+    { "delay",     "set delay time",    OFFSET(delay),     AV_OPT_TYPE_FLOAT, {.dbl=20}, 1, 100, A },
+    { "feedback",  "set feedback gain", OFFSET(feedback),  AV_OPT_TYPE_FLOAT, {.dbl=.3}, 0, 0.9, A },
+    { "crossfeed", "set cross feed",    OFFSET(crossfeed), AV_OPT_TYPE_FLOAT, {.dbl=.3}, 0, 0.8, A },
+    { "drymix",    "set dry-mix",       OFFSET(drymix),    AV_OPT_TYPE_FLOAT, {.dbl=.8}, 0, 1.0, A },
+    { NULL }
+};
+
+AVFILTER_DEFINE_CLASS(stereowiden);
+
+static int query_formats(AVFilterContext *ctx)
+{
+    AVFilterFormats *formats = NULL;
+    AVFilterChannelLayouts *layout = NULL;
+
+    ff_add_format(&formats, AV_SAMPLE_FMT_FLT);
+    ff_set_common_formats(ctx, formats);
+    ff_add_channel_layout(&layout, AV_CH_LAYOUT_STEREO);
+    ff_set_common_channel_layouts(ctx, layout);
+
+    formats = ff_all_samplerates();
+    if (!formats)
+        return AVERROR(ENOMEM);
+    return ff_set_common_samplerates(ctx, formats);
+}
+
+static int config_input(AVFilterLink *inlink)
+{
+    AVFilterContext *ctx = inlink->dst;
+    StereoWidenContext *s = ctx->priv;
+
+    s->length = 2 * s->delay * inlink->sample_rate / 1000;
+    s->buffer = av_calloc(s->length, sizeof(s->buffer));
+    if (!s->buffer)
+        return AVERROR(ENOMEM);
+    s->write = s->buffer;
+
+    return 0;
+}
+
+static int filter_frame(AVFilterLink *inlink, AVFrame *in)
+{
+    AVFilterContext *ctx = inlink->dst;
+    AVFilterLink *outlink = ctx->outputs[0];
+    StereoWidenContext *s = ctx->priv;
+    const float *src = (const float *)in->data[0];
+    const float drymix = s->drymix;
+    const float crossfeed = s->crossfeed;
+    const float feedback = s->feedback;
+    AVFrame *out = NULL;
+    float *dst;
+    int n;
+
+    if (av_frame_is_writable(in)) {
+        out = in;
+    } else {
+        AVFrame *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 = (float *)out->data[0];
+
+    for (n = 0; n < in->nb_samples; n++, src += 2, dst += 2) {
+        const float left = src[0], right = src[1];
+        float *read = s->write + 2;
+
+        if (read > s->buffer + s->length)
+            read = s->buffer;
+
+        dst[0] = drymix * left - crossfeed * right - feedback * read[1];
+        dst[1] = drymix * right - crossfeed * left - feedback * read[0];
+
+        s->write[0] = left;
+        s->write[1] = right;
+
+        if (s->write == s->buffer + s->length)
+            s->write = s->buffer;
+        else
+            s->write += 2;
+    }
+
+    if (out != in)
+        av_frame_free(&in);
+    return ff_filter_frame(outlink, out);
+}
+
+static av_cold void uninit(AVFilterContext *ctx)
+{
+    StereoWidenContext *s = ctx->priv;
+
+    av_freep(&s->buffer);
+}
+
+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_stereowiden = {
+    .name           = "stereowiden",
+    .description    = NULL_IF_CONFIG_SMALL("Apply stereo widening effect."),
+    .query_formats  = query_formats,
+    .priv_size      = sizeof(StereoWidenContext),
+    .priv_class     = &stereowiden_class,
+    .uninit         = uninit,
+    .inputs         = inputs,
+    .outputs        = outputs,
+};

libavfilter/allfilters.c

@@ -102,6 +102,7 @@ void avfilter_register_all(void)
     REGISTER_FILTER(SIDECHAINCOMPRESS, sidechaincompress, af);
     REGISTER_FILTER(SILENCEDETECT,  silencedetect,  af);
     REGISTER_FILTER(SILENCEREMOVE,  silenceremove,  af);
+    REGISTER_FILTER(STEREOWIDEN,    stereowiden,    af);
     REGISTER_FILTER(TREBLE,         treble,         af);
     REGISTER_FILTER(VOLUME,         volume,         af);
     REGISTER_FILTER(VOLUMEDETECT,   volumedetect,   af);

libavfilter/version.h

@@ -30,7 +30,7 @@
 #include "libavutil/version.h"
 
 #define LIBAVFILTER_VERSION_MAJOR   6
-#define LIBAVFILTER_VERSION_MINOR   3
+#define LIBAVFILTER_VERSION_MINOR   4
 #define LIBAVFILTER_VERSION_MICRO 100
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \