With live ingest you have the possibility to switch from playlist, or folder mode to a live stream.
It works in a way, that it create a ffmpeg instance in listen (server) mode. For example when you stream over RTMP to it, you can set the ingest input parameters to:
-f live_flv -listen 1 -i rtmp://0.0.0.0:1936/live/my-secrete-streaming-key
For SRT you could use:
-f mpegts -i 'srt://0.0.0.0:40077?mode=listener&passphrase=12345abcde'
Have in mind, that the ingest mode can't pull from a server, it only can act as its own server and listen for income.
When it notice a incoming stream, it will stop the current playing and continue the live source. The output will not interrupt, so you have a continuously output stream.
In rare cases it can happen, that for a short moment after switching the image freezes, but then it will continue. Also a short frame flickering can happen.
You need to know, that ffmpeg in current version has no authentication mechanism and it just listen to the protocol and port (no app and stream name).
ffplayout catches this problem with monitoring the output from ffmpeg. When the input is rtmp and the app or stream name differs to the config it stops the ingest process. So in a way we have a bit control, which stream we let come in and which not.
In theory you can use every protocol from ffmpeg which support a listen mode.