The app tries to provide the best video quality with a reasonable delay and without WiFi congestion. However, to obtain the best results, having a robust and reliable WiFi network is crucial.
We suggest using a modern WiFi access point with simultaneous dual-band (2.4GHz and 5GHz), supporting WMM and Apple Bonjour, while also having MIMO on both bands. MIMO is not used by every iOS device, but having it often means having a modern chipset.
We also suggest disabling Background App Refresh (in your iPhone Settings → General), and to avoid using apps which access the Internet in the background while you are streaming.
The video quality can also drop if the distance is too great for your network to handle. Sometimes moving the cameras closer together will help as well.