lavfi/overlay: show incoming frames on debug messages

This is especially useful to debug queue overflow issues.

Ideally we should be able to set the debug message at the
dualinput/framesync level, but they do not have the information related
to the filter context and the inlink, so cannot access much useful
information.
Signed-off-by: Stefano Sabatini <stefasab@gmail.com>

libavfilter/vf_overlay.c

@@ -34,6 +34,7 @@
 #include "libavutil/imgutils.h"
 #include "libavutil/mathematics.h"
 #include "libavutil/opt.h"
+#include "libavutil/timestamp.h"
 #include "internal.h"
 #include "dualinput.h"
 #include "drawutils.h"
@@ -576,6 +577,7 @@ static AVFrame *do_blend(AVFilterContext *ctx, AVFrame *mainpic,
 static int filter_frame(AVFilterLink *inlink, AVFrame *inpicref)
 {
     OverlayContext *s = inlink->dst->priv;
+    av_log(inlink->dst, AV_LOG_DEBUG, "Incoming frame (time:%s) from link #%d\n", av_ts2timestr(inpicref->pts, &inlink->time_base), FF_INLINK_IDX(inlink));
     return ff_dualinput_filter_frame(&s->dinput, inlink, inpicref);
 }