Not sure exactly what you'd do in Windows, but this is some really basic OS scripting outside of Tvheadend.
I do more-or-less the same thing for my ONVIF cameras. The cameras each have an RTSP server, so I use openrtsp to receive the stream which enables me to limit the duration of each file.
If you use curl you can use the --max-file-size command line parameter.
What you would do is create a batch script, powershell script, whatever, for each source - or one that you can pass parameters into. The batch script would have an infinite loop. On each iteration you would call curl with the URL for the channel (probably using the pass or htsp profile) and a maximum size, and the output file including whatever information you need - e.g. date, time, channel name. On termination, you would check the size of all the files in the directory ("folder") and if it exceeds a certain amount (e.g. 2TB), delete the oldest. Then the loop goes back to the start.
