avfilter: add extrastereo filter

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

Changelog

@@ -3,6 +3,7 @@ releases are sorted from youngest to oldest.
 
 version <next>:
 - DXV decoding
+- extrastereo filter
 
 
 version 2.8:

doc/filters.texi

@@ -1817,6 +1817,23 @@ equalizer=f=1000:width_type=q:width=1:g=2,equalizer=f=100:width_type=q:width=2:g
 @end example
 @end itemize
 
+@section extrastereo
+
+Linearly increases the difference between left and right channels which
+adds some sort of "live" effect to playback.
+
+The filter accepts the following option:
+
+@table @option
+@item m
+Sets the difference coefficient (default: 2.5). 0.0 means mono sound
+(average of both channels), with 1.0 sound will be unchanged, with
+-1.0 left and right channels will be swapped.
+
+@item c
+Enable clipping. By default is enabled.
+@end table
+
 @section flanger
 Apply a flanging effect to the audio.
 

libavfilter/Makefile

@@ -67,6 +67,7 @@ OBJS-$(CONFIG_DYNAUDNORM_FILTER)             += af_dynaudnorm.o
 OBJS-$(CONFIG_EARWAX_FILTER)                 += af_earwax.o
 OBJS-$(CONFIG_EBUR128_FILTER)                += f_ebur128.o
 OBJS-$(CONFIG_EQUALIZER_FILTER)              += af_biquads.o
+OBJS-$(CONFIG_EXTRASTEREO_FILTER)            += af_extrastereo.o
 OBJS-$(CONFIG_FLANGER_FILTER)                += af_flanger.o generate_wave_table.o
 OBJS-$(CONFIG_HIGHPASS_FILTER)               += af_biquads.o
 OBJS-$(CONFIG_JOIN_FILTER)                   += af_join.o

libavfilter/af_extrastereo.c

@@ -0,0 +1,128 @@
+/*
+ * Copyright (c) 2015 The FFmpeg Project
+ *
+ * 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 ExtraStereoContext {
+    const AVClass *class;
+    float mult;
+    int clip;
+} ExtraStereoContext;
+
+#define OFFSET(x) offsetof(ExtraStereoContext, x)
+#define A AV_OPT_FLAG_AUDIO_PARAM|AV_OPT_FLAG_FILTERING_PARAM
+
+static const AVOption extrastereo_options[] = {
+    { "m", "set the difference coefficient", OFFSET(mult), AV_OPT_TYPE_FLOAT, {.dbl=2.5}, -10, 10, A },
+    { "c", "enable clipping",                OFFSET(clip), AV_OPT_TYPE_INT,   {.i64=1},     0,  1, A },
+    { NULL }
+};
+
+AVFILTER_DEFINE_CLASS(extrastereo);
+
+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 filter_frame(AVFilterLink *inlink, AVFrame *in)
+{
+    AVFilterContext *ctx = inlink->dst;
+    AVFilterLink *outlink = ctx->outputs[0];
+    ExtraStereoContext *s = ctx->priv;
+    const float *src = (const float *)in->data[0];
+    const float mult = s->mult;
+    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++) {
+        float average, left, right;
+
+        left    = src[n * 2    ];
+        right   = src[n * 2 + 1];
+        average = (left + right) / 2.;
+        left    = average + mult * (left  - average);
+        right   = average + mult * (right - average);
+
+        if (s->clip) {
+            dst[n * 2    ] = av_clipf(left,  -1, 1);
+            dst[n * 2 + 1] = av_clipf(right, -1, 1);
+        }
+    }
+
+    if (out != in)
+        av_frame_free(&in);
+    return ff_filter_frame(outlink, out);
+}
+
+static const AVFilterPad inputs[] = {
+    {
+        .name         = "default",
+        .type         = AVMEDIA_TYPE_AUDIO,
+        .filter_frame = filter_frame,
+    },
+    { NULL }
+};
+
+static const AVFilterPad outputs[] = {
+    {
+        .name = "default",
+        .type = AVMEDIA_TYPE_AUDIO,
+    },
+    { NULL }
+};
+
+AVFilter ff_af_extrastereo = {
+    .name           = "extrastereo",
+    .description    = NULL_IF_CONFIG_SMALL("Increase difference between stereo audio channels."),
+    .query_formats  = query_formats,
+    .priv_size      = sizeof(ExtraStereoContext),
+    .priv_class     = &extrastereo_class,
+    .inputs         = inputs,
+    .outputs        = outputs,
+};

libavfilter/allfilters.c

@@ -89,6 +89,7 @@ void avfilter_register_all(void)
     REGISTER_FILTER(EARWAX,         earwax,         af);
     REGISTER_FILTER(EBUR128,        ebur128,        af);
     REGISTER_FILTER(EQUALIZER,      equalizer,      af);
+    REGISTER_FILTER(EXTRASTEREO,    extrastereo,    af);
     REGISTER_FILTER(FLANGER,        flanger,        af);
     REGISTER_FILTER(HIGHPASS,       highpass,       af);
     REGISTER_FILTER(JOIN,           join,           af);

libavfilter/version.h

@@ -30,7 +30,7 @@
 #include "libavutil/version.h"
 
 #define LIBAVFILTER_VERSION_MAJOR   6
-#define LIBAVFILTER_VERSION_MINOR   0
+#define LIBAVFILTER_VERSION_MINOR   1
 #define LIBAVFILTER_VERSION_MICRO 100
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \