1. As WebRTC client, it will auto adjust the sending video fps/resolution/bitrate according to the network bandwidth. For subscribed mix stream, the bitrate will do auto adjustment, and resolution need to be switched manually through MCU multi-streaming, but fps is fixed for each resolution now.
2. You can manually enable/disable local video stream and notify MCU to play/pause video stream to achieve audio only chat if you found network quality is bad through network stats API.