avfilter: add tremolo filter

Signed-off-by: Kyle Swanson <k@ylo.ph>

Changelog

@@ -9,6 +9,7 @@ version <next>:
 - stereowiden filter
 - stereotools filter
 - rubberband filter
+- tremolo filter
 
 
 version 2.8:

doc/filters.texi

@@ -2568,6 +2568,25 @@ slope
 Determine how steep is the filter's shelf transition.
 @end table
 
+@section tremolo
+
+Sinusoidal amplitude modulation.
+
+The filter accepts the following options:
+
+@table @option
+@item f
+Modulation frequency in Hertz. Modulation frequencies in the subharmonic range
+(20 Hz or lower) will result in a tremolo effect.
+This filter may also be used as a ring modulator by specifying
+a modulation frequency higher than 20 Hz.
+Range is 0.1 - 20000.0. Default value is 5.0 Hz.
+
+@item d
+Depth of modulation as a percentage. Range is 0.0 - 1.0.
+Default value is 0.5.
+@end table
+
 @section volume
 
 Adjust the input audio volume.

libavfilter/Makefile

@@ -84,6 +84,7 @@ OBJS-$(CONFIG_SILENCEREMOVE_FILTER)          += af_silenceremove.o
 OBJS-$(CONFIG_STEREOTOOLS_FILTER)            += af_stereotools.o
 OBJS-$(CONFIG_STEREOWIDEN_FILTER)            += af_stereowiden.o
 OBJS-$(CONFIG_TREBLE_FILTER)                 += af_biquads.o
+OBJS-$(CONFIG_TREMOLO_FILTER)                += af_tremolo.o generate_wave_table.o
 OBJS-$(CONFIG_VOLUME_FILTER)                 += af_volume.o
 OBJS-$(CONFIG_VOLUMEDETECT_FILTER)           += af_volumedetect.o
 

libavfilter/af_tremolo.c

+/*
+ * Copyright (c) 2015 Kyle Swanson <k@ylo.ph>.
+ *
+ * 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/opt.h"
+#include "avfilter.h"
+#include "internal.h"
+#include "audio.h"
+#include "generate_wave_table.h"
+
+typedef struct TremoloContext {
+    const AVClass *class;
+    double freq;
+    double depth;
+    double *wave_table;
+    int wave_table_index;
+    int sample_rate;
+} TremoloContext;
+
+#define OFFSET(x) offsetof(TremoloContext, x)
+#define FLAGS AV_OPT_FLAG_AUDIO_PARAM|AV_OPT_FLAG_FILTERING_PARAM
+
+static const AVOption tremolo_options[] = {
+    { "f", "set frequency in hertz",    OFFSET(freq),    AV_OPT_TYPE_DOUBLE,   {.dbl = 5.0},   0.1,   20000.0, FLAGS },
+    { "d", "set depth as percentage",   OFFSET(depth),   AV_OPT_TYPE_DOUBLE,   {.dbl = 0.5},   0.0,   1.0,     FLAGS },
+    { NULL }
+};
+
+AVFILTER_DEFINE_CLASS(tremolo);
+
+static double trem_env(AVFilterContext *ctx)
+{
+    TremoloContext *s = ctx->priv;
+    double env = s->wave_table[s->wave_table_index];
+    s->wave_table_index++;
+    if (s->wave_table_index >= s->sample_rate / s->freq)
+        s->wave_table_index = 0;
+    return 1.0 - (s->depth * env);
+}
+
+static int filter_frame(AVFilterLink *inlink, AVFrame *in)
+{
+    AVFilterContext *ctx = inlink->dst;
+    AVFilterLink *outlink = ctx->outputs[0];
+    const double *src = (const double *)in->data[0];
+    const int channels = inlink->channels;
+    const int nb_samples = in->nb_samples;
+    AVFrame *out;
+    double *dst;
+    int n, c;
+
+    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 < nb_samples; n++) {
+        const double env = trem_env(ctx);
+
+        for (c = 0; c < channels; c++)
+            dst[c] = src[c] * env;
+        dst += channels;
+        src += channels;
+    }
+
+    if (in != out)
+        av_frame_free(&in);
+
+    return ff_filter_frame(outlink, out);
+}
+
+static int query_formats(AVFilterContext *ctx)
+{
+    AVFilterFormats *formats;
+    AVFilterChannelLayouts *layouts;
+    static const enum AVSampleFormat sample_fmts[] = {
+        AV_SAMPLE_FMT_DBL,
+        AV_SAMPLE_FMT_NONE
+    };
+    int ret;
+
+    layouts = ff_all_channel_counts();
+    if (!layouts)
+        return AVERROR(ENOMEM);
+    ret = ff_set_common_channel_layouts(ctx, layouts);
+    if (ret < 0)
+        return ret;
+
+    formats = ff_make_format_list(sample_fmts);
+    if (!formats)
+        return AVERROR(ENOMEM);
+    ret = ff_set_common_formats(ctx, formats);
+    if (ret < 0)
+        return ret;
+
+    formats = ff_all_samplerates();
+    if (!formats)
+        return AVERROR(ENOMEM);
+    return ff_set_common_samplerates(ctx, formats);
+}
+
+static av_cold void uninit(AVFilterContext *ctx)
+{
+    TremoloContext *s = ctx->priv;
+    av_freep(&s->wave_table);
+}
+
+static int config_input(AVFilterLink *inlink)
+{
+    AVFilterContext *ctx = inlink->dst;
+    TremoloContext *s = ctx->priv;
+
+    s->sample_rate = inlink->sample_rate;
+    s->wave_table = av_malloc_array(s->sample_rate / s->freq, sizeof(*s->wave_table));
+    if (!s->wave_table)
+        return AVERROR(ENOMEM);
+
+    ff_generate_wave_table(WAVE_SIN, AV_SAMPLE_FMT_DBL, s->wave_table, s->sample_rate / s->freq, 0.0, 1.0, 0.0);
+    s->wave_table_index = 0;
+    return 0;
+}
+
+static const AVFilterPad avfilter_af_tremolo_inputs[] = {
+    {
+        .name         = "default",
+        .type         = AVMEDIA_TYPE_AUDIO,
+        .config_props = config_input,
+        .filter_frame = filter_frame,
+    },
+    { NULL }
+};
+
+static const AVFilterPad avfilter_af_tremolo_outputs[] = {
+    {
+        .name = "default",
+        .type = AVMEDIA_TYPE_AUDIO,
+    },
+    { NULL }
+};
+
+AVFilter ff_af_tremolo = {
+    .name          = "tremolo",
+    .description   = NULL_IF_CONFIG_SMALL("Apply tremolo effect."),
+    .priv_size     = sizeof(TremoloContext),
+    .priv_class    = &tremolo_class,
+    .uninit        = uninit,
+    .query_formats = query_formats,
+    .inputs        = avfilter_af_tremolo_inputs,
+    .outputs       = avfilter_af_tremolo_outputs,
+};

libavfilter/allfilters.c

@@ -106,6 +106,7 @@ void avfilter_register_all(void)
     REGISTER_FILTER(STEREOTOOLS,    stereotools,    af);
     REGISTER_FILTER(STEREOWIDEN,    stereowiden,    af);
     REGISTER_FILTER(TREBLE,         treble,         af);
+    REGISTER_FILTER(TREMOLO,        tremolo,        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   6
+#define LIBAVFILTER_VERSION_MINOR   7
 #define LIBAVFILTER_VERSION_MICRO 100
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \