Currently we use a modified WebRTC stack with VP8/VP9 to encode the video stream. This is similar to what quite a few game streaming services are doing like Stadia and even Amazon's new Luna(?) service. There are lots of platform specific optimizations up and down the webrtc stack to make sure latency is kept to a minimum while preserving quality. Things like only encoding pixels that change, progressively encoding over multiple frames to sharpen quality, keeping jitter buffers to a minimum.