avfilter/af_agate: add level_sc option for sidechaingate filter

Also correct usage of input gain for both filters.
Signed-off-by: NPaul B Mahol <onemda@gmail.com>

doc/filters.texi

@@ -2656,6 +2656,9 @@ Default is peak. Can be peak or rms.
 Choose if the average level between all channels or the louder channel affects
 the reduction.
 Default is average. Can be average or maximum.
+
+@item level_sc
+Set sidechain gain. Default is 1. Range is from 0.015625 to 64.
 @end table
 
 @section silencedetect

libavfilter/af_agate.c

@@ -35,6 +35,7 @@ typedef struct AudioGateContext {
     const AVClass *class;
 
     double level_in;
+    double level_sc;
     double attack;
     double release;
     double threshold;
@@ -74,6 +75,7 @@ static const AVOption options[] = {
     { "link",      "set link",               OFFSET(link),      AV_OPT_TYPE_INT,    {.i64=0},           0,    1, A, "link" },
     {   "average", 0,                        0,                 AV_OPT_TYPE_CONST,  {.i64=0},           0,    0, A, "link" },
     {   "maximum", 0,                        0,                 AV_OPT_TYPE_CONST,  {.i64=1},           0,    0, A, "link" },
+    { "level_sc",  "set sidechain gain",     OFFSET(level_sc),  AV_OPT_TYPE_DOUBLE, {.dbl=1},           0.015625,   64, A },
     { NULL }
 };
 
@@ -158,27 +160,25 @@ static double output_gain(double lin_slope, double ratio, double thres,
     return 1.;
 }
 
-static void gate(AudioGateContext *s, const double *src, double *dst, const double *scsrc,
-                 int nb_samples, AVFilterLink *inlink, AVFilterLink *sclink)
+static void gate(AudioGateContext *s,
+                 const double *src, double *dst, const double *scsrc,
+                 int nb_samples, double level_in, double level_sc,
+                 AVFilterLink *inlink, AVFilterLink *sclink)
 {
     const double makeup = s->makeup;
     const double attack_coeff = s->attack_coeff;
     const double release_coeff = s->release_coeff;
-    const double level_in = s->level_in;
     int n, c;
 
     for (n = 0; n < nb_samples; n++, src += inlink->channels, dst += inlink->channels, scsrc += sclink->channels) {
-        double abs_sample = fabs(scsrc[0]), gain = 1.0;
-
-        for (c = 0; c < inlink->channels; c++)
-            dst[c] = src[c] * level_in;
+        double abs_sample = fabs(scsrc[0] * level_sc), gain = 1.0;
 
         if (s->link == 1) {
             for (c = 1; c < sclink->channels; c++)
-                abs_sample = FFMAX(fabs(scsrc[c]), abs_sample);
+                abs_sample = FFMAX(fabs(scsrc[c] * level_sc), abs_sample);
         } else {
             for (c = 1; c < sclink->channels; c++)
-                abs_sample += fabs(scsrc[c]);
+                abs_sample += fabs(scsrc[c] * level_sc);
 
             abs_sample /= sclink->channels;
         }
@@ -193,7 +193,7 @@ static void gate(AudioGateContext *s, const double *src, double *dst, const doub
                                s->lin_knee_stop, s->range);
 
         for (c = 0; c < inlink->channels; c++)
-            dst[c] *= gain * makeup;
+            dst[c] = src[c] * level_in * gain * makeup;
     }
 }
 
@@ -218,7 +218,8 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
     }
     dst = (double *)out->data[0];
 
-    gate(s, src, dst, src, in->nb_samples, inlink, inlink);
+    gate(s, src, dst, src, in->nb_samples,
+         s->level_in, s->level_in, inlink, inlink);
 
     if (out != in)
         av_frame_free(&in);
@@ -284,6 +285,7 @@ static int scfilter_frame(AVFilterLink *link, AVFrame *in)
     scsrc = (const double *)s->input_frame[1]->data[0];
 
     gate(s, sample, sample, scsrc, nb_samples,
+         s->level_in, s->level_sc,
          ctx->inputs[0], ctx->inputs[1]);
     ret = ff_filter_frame(outlink, s->input_frame[0]);