ffmpeg: warn that -t does not work with -filter_complex.

ffmpeg.c

@@ -4943,6 +4943,9 @@ static void init_output_filter(OutputFilter *ofilter, OptionsContext *o,
                "cannot be used together.\n", ost->file_index, ost->index);
         exit_program(1);
     }
+    if (o->recording_time != INT64_MAX)
+        av_log(NULL, AV_LOG_WARNING,
+               "-t does not work with -filter_complex (yet).\n");
 
     if (configure_output_filter(ofilter->graph, ofilter, ofilter->out_tmp) < 0) {
         av_log(NULL, AV_LOG_FATAL, "Error configuring filter.\n");