ffmpeg: make loglevel verbose for frame duration warning

fftools/ffmpeg.c

@@ -1121,7 +1121,7 @@ static void do_video_out(OutputFile *of,
             format_video_sync != VSYNC_PASSTHROUGH &&
             format_video_sync != VSYNC_DROP) {
             if (delta0 < -0.6) {
-                av_log(NULL, AV_LOG_WARNING, "Past duration %f too large\n", -delta0);
+                av_log(NULL, AV_LOG_VERBOSE, "Past duration %f too large\n", -delta0);
             } else
                 av_log(NULL, AV_LOG_DEBUG, "Clipping frame in rate conversion by %f\n", -delta0);
             sync_ipts = ost->sync_opts;