The Browser based speedtest function (:8089/speedtest) is a very handy tool to determine where network bottlenecks are located. Could you add the same functionality to both the IOS and TvOS apps as well? Perhaps in the "Settings/DVR" section ?
Unfortunately tvOS doesn't have a web browser we can use. For iOS, adding speedtest is on our todo list.
There is a FREE Speedtest App for tvOS and iOS. Search the App Store for it. I believe same company that produces speedtest.net. OK.... is company name.
There is also a Network Speed Tester available but it may cost $1 or something like that. I run a copy on my iMac and my tvOS from time to time but the Free Speedtest App usually pin points what I am looking for.
Network speedtest measures the throughput from a web browser (or app on the appletv) to a server somewhere "out on the internet." I wish to measure the throughput from the appletv to the server hosting the DVR (a very different metric).. If you are accessing the DVR "away from home" this would include bottlenecks at both ends. An adding iperf3 code to the server and client tvOS app should (IMO) not be that difficult - except that everything now runs over a single TCP/IP port.
You are correct that the SPEEDTEST App on the Apple TV (tvOS) or iPhone (iOS) measures the throughput to a server somewhere "out on the internet" - I.E. "WAN".
BUT, not true about the "Network Speed Tester" I mentioned. This later test is within the "LAN". And I use it to test between my iMac on my "LAN" and my Apple TV on my "LAN".
However, if your are hosting on a Windows Machine I believe you would need another utility.
I agree if Channels would add a feature from say tvOS App to the DVR that would be best for this particular test.