AVPro Video has an option "Force RTP TCP" to force Android ExoPlayer to play RTSP live stream with TCP.
This is disabled by default. So currently it seems that underlying ExoPlayer tries to connect with UDP firstly, then fallback to TCP. This fallback causes about 10 seconds delay to play our TopazChat live stream (and also VRCDN).
Enabling this option will skip UDP connection trying, so the time to start playback could be faster.
Playing RTSP source with UDP will not be used commonly, because most users connect Quest to their routers with NAT enabled. RTSP itself has no mechanism to connect UDP over NAT, so RTSP over UDP will be used only in LAN which is not a main usage of VRChat.