[FFmpeg-devel] [PATCH] libavfilter/af_ambisonic.c Added File for Ambisonic Filter

[Sanchit Sinha]

libavfilter/af_ambisonic.c | 139
+++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 139 insertions(+)
 create mode 100644 libavfilter/af_ambisonic.c

diff --git a/libavfilter/af_ambisonic.c b/libavfilter/af_ambisonic.c
new file mode 100644
index 0000000..98b0e44
--- /dev/null
+++ b/libavfilter/af_ambisonic.c
@@ -0,0 +1,139 @@
+/*
+ * 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 <stdio.h>
+#include "libavutil/avstring.h"
+#include "libavutil/channel_layout.h"
+#include "libavutil/opt.h"
+#include "audio.h"
+#include "avfilter.h"
+#include "formats.h"
+
+#define root8 2.828
+
+typedef struct AmbisonicContext {
+    const AVClass *class;
+    /*Not needed, if any new variables are to be used, this struct can be
populated*/
+
+} AmbisonicContext;
+
+#define OFFSET(x) offsetof(AmbisonicContext, x) //Future use(maybe)
+
+static const AVOption ambisonic_options[] = {  //square will be an option
+{NULL}
+};
+
+AVFILTER_DEFINE_CLASS(ambisonic);
+static int query_formats(AVFilterContext *ctx)
+{
+    AVFilterFormats *formats = NULL;
+    AVFilterChannelLayouts *layout = NULL;
+    int ret;
+        if ((ret = ff_add_format             (&formats, AV_SAMPLE_FMT_FLTP
  )) < 0 ||
+        (ret = ff_set_common_formats         (ctx     , formats
 )) < 0 ||
+        (ret = ff_add_channel_layout         (&layout ,
AV_CH_LAYOUT_4POINT0)) < 0 ||
+        (ret = ff_set_common_channel_layouts (ctx     , layout
)) < 0)
+        return ret;
+    formats = ff_all_samplerates();
+    return ff_set_common_samplerates(ctx, formats);
+}
+static int filter_frame(AVFilterLink *inlink, AVFrame *in)
+{
+    AVFilterContext *ctx = inlink->dst;
+    AVFilterLink *outlink = ctx->outputs[0];
+    /*If variables used, this has to be created*/
+    // AmbisonicContext *s = ctx->priv;
+    // const float *src = (const float *)in->data[0];
+    // float *dst;
+    float *lf,*lb,*rb,*rf;
+    AVFrame *out;
+    int itr;
+    float *w,*x,*y;
+
+    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);
+    }
+
+    /*If planar samples are used, output must be put in dst*/
+    //dst = (float *)out->data[0];
+
+    lf = (float *)malloc(sizeof(float));
+    lb = (float *)malloc(sizeof(float));
+    rb = (float *)malloc(sizeof(float));
+    rf = (float *)malloc(sizeof(float));
+
+    for(itr=0;itr<in->nb_samples;itr++)
+    {
+        *lf=0,*lb=0,*rb=0,*rf=0;
+        /*Float pointers to the samples*/
+        w=(float *)(*(in->extended_data)+itr);
+        x=(float *)(*(in->extended_data+1)+itr);
+        y=(float *)(*(in->extended_data+2)+itr);
+
+        *lf = root8 * (2*(*w)+*x+*y);
+        *lb = root8 * (2*(*w)-*x+*y);
+        *rb = root8 * (2*(*w)-*x-*y);
+        *rf = root8 * (2*(*w)+*x-*y);
+
+        /*Mathematical coefficients taken from :
https://en.wikipedia.org/wiki/Ambisonics*/
+        out->extended_data[0][itr]= *lf;
+        out->extended_data[1][itr]= *lb;
+        out->extended_data[2][itr]= *rb;
+        out->extended_data[3][itr]= *rf;
+    }
+
+    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,
+        // .config_props = config_input,
+    },
+    { NULL }
+};
+
+static const AVFilterPad outputs[] = {
+    {
+        .name = "default",
+        .type = AVMEDIA_TYPE_AUDIO,
+    },
+    { NULL }
+};
+
+AVFilter ff_af_ambisonic = {
+    .name           = "ambisonic",
+    .description    = NULL_IF_CONFIG_SMALL("An ambisonic filter"),
+    .query_formats  = query_formats,
+    .priv_size      = sizeof(AmbisonicContext),
+    .priv_class     = &ambisonic_class,
+    // .uninit         = uninit,
+    .inputs         = inputs,
+    .outputs        = outputs,
+};
\ No newline at end of file
-- 
2.7.4