Is it possible to use the same PlainTransport for both audio producer and video producer？
I modified <mediasoup-demo/broadcasters/gstreamer.sh> to use the same PlainTransport for both audio producer and video producer. But there is only audio on the web page and no video.
Yes, of course it’s possible. But your problem is not with mediasoup but without gstreamer. You need to make it capable of sending and receiving using the same RTP tuple.
It is possible, you should use only one IP tuple and introduce a funnel element (or the new rtpfunnel rtpfunnel) in order to mix multiple rtp flows on the same UDP connection.