wait for audience(rtsp server) to complete starting

[yjjnls]

When adding an audience(rtsp server) in a livestream, you have to wait for at least 500ms, then you can start the rtsp analyzer. Or the rtsp analyzer can't get data.

[yjjnls]

The test is described below:
rtsp test server ->livestreeam -> audience(rtsp server) -> rtsp analyzer

here rtsp test server is used as the test source, but if it's replaced with some independent rtsp source, such as IPC or rtspserver(gst-launch), rtsp analyzer will get data even without time wait.