avfilter/showvolume : calculate fade only if fade < 1.

libavfilter/avf_showvolume.c

@@ -273,6 +273,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *insamples)
     }
     s->out->pts = insamples->pts;
 
+    if (s->f < 1.) {
     for (j = 0; j < outlink->h; j++) {
         uint8_t *dst = s->out->data[0] + j * s->out->linesize[0];
         const uint32_t alpha = s->bgopacity * 255;
@@ -284,6 +285,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *insamples)
             dst[k * 4 + 3] = FFMAX(dst[k * 4 + 3] * s->f, alpha);
         }
     }
+    }
 
     if (s->orientation) { /* vertical */
         for (c = 0; c < inlink->channels; c++) {