OK finally got working PeerTube 3.4.1 on Nvidia Jetson Nano with hardware transcoding. Pics show live transcoding 720p -> 360p. Jetson load is ~1, would hadle more streams. I will set up PeerTube to transcode all uploads to 360p to allow people on slow connections watch too.
FFmpeg NVMPI encoder https://github.com/jocover/jetson-ffmpeg
PeerTube transcoding profiles plugin https://framagit.org/framasoft/peertube/official-plugins/tree/master/peertube-plugin-transcoding-profile-debug