avfilter/avf_avectorscope: add possibility to auto zoom

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

doc/filters.texi

@@ -17044,7 +17044,8 @@ Specify the red, green, blue and alpha fade. Default values are @code{15},
 Allowed range is @code{[0, 255]}.
 
 @item zoom
-Set the zoom factor. Default value is @code{1}. Allowed range is @code{[1, 10]}.
+Set the zoom factor. Default value is @code{1}. Allowed range is @code{[0, 10]}.
+Values lower than @var{1} will auto adjust zoom factor to maximal possible value.
 
 @item draw
 Set the vectorscope drawing mode.

libavfilter/avf_avectorscope.c

@@ -90,7 +90,7 @@ static const AVOption avectorscope_options[] = {
     { "gf", "set green fade",     OFFSET(fade[1]), AV_OPT_TYPE_INT, {.i64=10}, 0, 255, FLAGS },
     { "bf", "set blue fade",      OFFSET(fade[2]), AV_OPT_TYPE_INT, {.i64=5},  0, 255, FLAGS },
     { "af", "set alpha fade",     OFFSET(fade[3]), AV_OPT_TYPE_INT, {.i64=5},  0, 255, FLAGS },
-    { "zoom", "set zoom factor",  OFFSET(zoom), AV_OPT_TYPE_DOUBLE, {.dbl=1},  1, 10, FLAGS },
+    { "zoom", "set zoom factor",  OFFSET(zoom), AV_OPT_TYPE_DOUBLE, {.dbl=1},  0, 10, FLAGS },
     { "draw", "set draw mode", OFFSET(draw), AV_OPT_TYPE_INT, {.i64=DOT}, 0, DRAW_NB-1, FLAGS, "draw" },
     { "dot",   "", 0, AV_OPT_TYPE_CONST, {.i64=DOT} , 0, 0, FLAGS, "draw" },
     { "line",  "", 0, AV_OPT_TYPE_CONST, {.i64=LINE}, 0, 0, FLAGS, "draw" },
@@ -234,7 +234,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *insamples)
     const int hh = s->hh;
     unsigned x, y;
     unsigned prev_x = s->prev_x, prev_y = s->prev_y;
-    const double zoom = s->zoom;
+    double zoom = s->zoom;
     int i;
 
     if (!s->outpicref || s->outpicref->width  != outlink->w ||
@@ -254,6 +254,35 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *insamples)
 
     fade(s);
 
+    if (zoom < 1) {
+        float max = 0;
+
+        switch (insamples->format) {
+        case AV_SAMPLE_FMT_S16: {
+            int16_t *samples = (int16_t *)insamples->data[0];
+
+            for (i = 0; i < insamples->nb_samples * 2; i++) {
+                float sample = samples[i] / (float)INT16_MAX;
+                max = FFMAX(FFABS(sample), max);
+            }
+
+            }
+            break;
+        case AV_SAMPLE_FMT_FLT: {
+            float *samples = (float *)insamples->data[0] + i * 2;
+
+            for (i = 0; i < insamples->nb_samples; i++) {
+                max = FFMAX(FFABS(samples[i]), max);
+            }
+            }
+            break;
+        default:
+            av_assert2(0);
+        }
+
+        zoom = 1. / max;
+    }
+
     for (i = 0; i < insamples->nb_samples; i++) {
         int16_t *samples = (int16_t *)insamples->data[0] + i * 2;
         float *samplesf = (float *)insamples->data[0] + i * 2;