ffmpeg: check for unsupported "queing of command on first filter supporting the specific commend"

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

ffmpeg.c

@@ -2698,6 +2698,9 @@ static int check_keyboard_interaction(int64_t cur_time)
                         ret = avfilter_graph_send_command(fg->graph, target, command, arg, buf, sizeof(buf),
                                                           key == 'c' ? AVFILTER_CMD_FLAG_ONE : 0);
                         fprintf(stderr, "Command reply for stream %d: ret:%d res:\n%s", i, ret, buf);
+                    } else if (key == 'c') {
+                        fprintf(stderr, "Queing commands only on filters supporting the specific command is unsupported\n");
+                        ret = AVERROR_PATCHWELCOME;
                     } else {
                         ret = avfilter_graph_queue_command(fg->graph, target, command, arg, 0, time);
                     }