avfilter/vf_delogo: add auto set the area inside of the frame

when the area outside of the frame, then use expr should
give user warning message and auto set to the area inside of the frame.
Signed-off-by: Steven Liu <lq@chinaffmpeg.org>

libavfilter/vf_delogo.c

@@ -327,6 +327,21 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
     s->w = av_expr_eval(s->w_pexpr, s->var_values, s);
     s->h = av_expr_eval(s->h_pexpr, s->var_values, s);
 
+    if (s->x + (s->band - 1) <= 0 || s->x + s->w - (s->band*2 - 2) > inlink->w ||
+        s->y + (s->band - 1) <= 0 || s->y + s->h - (s->band*2 - 2) > inlink->h) {
+        av_log(s, AV_LOG_WARNING, "Logo area is outside of the frame,"
+               " auto set the area inside of the frame\n");
+    }
+
+    if (s->x + (s->band - 1) <= 0)
+        s->x = 1 + s->band;
+    if (s->y + (s->band - 1) <= 0)
+        s->y = 1 + s->band;
+    if (s->x + s->w - (s->band*2 - 2) > inlink->w)
+        s->w = inlink->w - s->x - (s->band*2 - 2);
+    if (s->y + s->h - (s->band*2 - 2) > inlink->h)
+        s->h = inlink->h - s->y - (s->band*2 - 2);
+
     ret = config_input(inlink);
     if (ret < 0) {
         av_frame_free(&in);