The general way to do this is to use ffmpeg to stream an flv formatted stream to a 3rd party RTMP server, like YouTube Live. Then you can embed the resulting YouTube live stream into the HTML Widget on Thingsboard as an object. I have this working on my end, however, there are some YouTube specific limitations in that if the stream stops, the streaming URL Key changes, so you have to get a new Key from YouTube GUI which is unfortunate because it requires human intervention.