avfilter/vf_vfrdet: also report average delta

doc/filters.texi

@@ -18946,8 +18946,8 @@ This filter tries to detect if the input is variable or constant frame rate.
 
 At end it will output number of frames detected as having variable delta pts,
 and ones with constant delta pts.
-If there was frames with variable delta, than it will also show min and max delta
-encountered.
+If there was frames with variable delta, than it will also show min, max and
+average delta encountered.
 
 @section vibrance
 

libavfilter/vf_vfrdet.c

@@ -29,6 +29,7 @@ typedef struct VFRDETContext {
     int64_t delta;
     int64_t min_delta;
     int64_t max_delta;
+    int64_t avg_delta;
 
     uint64_t vfr;
     uint64_t cfr;
@@ -53,6 +54,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
             s->delta = delta;
             s->min_delta = FFMIN(delta, s->min_delta);
             s->max_delta = FFMAX(delta, s->max_delta);
+            s->avg_delta += delta;
         } else {
             s->cfr++;
         }
@@ -81,7 +83,7 @@ static av_cold void uninit(AVFilterContext *ctx)
 
     av_log(ctx, AV_LOG_INFO, "VFR:%f (%"PRIu64"/%"PRIu64")", s->vfr / (float)(s->vfr + s->cfr), s->vfr, s->cfr);
     if (s->vfr)
-        av_log(ctx, AV_LOG_INFO, " min: %"PRId64" max: %"PRId64")", s->min_delta, s->max_delta);
+        av_log(ctx, AV_LOG_INFO, " min: %"PRId64" max: %"PRId64" avg: %"PRId64, s->min_delta, s->max_delta, s->avg_delta / s->vfr);
     av_log(ctx, AV_LOG_INFO, "\n");
 }