It is possible to stream to Twitch using the ffmpeg command-line program very easily by just using an RTMP transport and knowing a stream key. For example, the following command:
ffmpeg -hide_banner -loglevel error -y -i "rtsp://user:password@HOST.TLD/stream1" -c:v copy -c:a copy -f flv "rtmp://live-fra.twitch.tv/app/live_645677534_EcJuiWNVddkejUEKSLKDJNJE"
where:
user and password are credentials,HOST.TLD is the hostname corresponding to the Tapo camera,live_645677534_EcJuiWNVddkejUEKSLKDJNJE is a Twitch stream key taken from an account
will grab video from the camera and stream the video to Twitch. It is also possible to combine streams by using multiple -i flags representing multiple inputs. Ultimately, OBS just does some sophisticated parameter interpolation behind the scenes that renders the stream to Twitch in a convenient and user-friendly manner but ffmpeg is what it uses.