Found a solution.
See also: https://community.home-assistant.io/t/solved-2-way-audio-with-frigate-tapo-cameras-c320ws/793219
The following configuration works.
Note the go2rtc -> streams ->
Is the same as the cameras ->
They use the same IP address.
This is a Tapo C120 cam.
Note the "tapo://" protocol (this enabled 2-way audio) requires only the password, and device IP without a port number or URI path.
config.yaml
go2rtc:
streams:
living_room:
- rtsp://username:password@xxx.xxx.xxx.123:554/stream1
- tapo://password@xxx.xxx.xxx.123
cameras:
living_room:
enabled: true
ffmpeg:
inputs:
- path: rtsp://username:password@xxx.xxx.xxx.123:554/stream1
roles:
- detect
...
...