I have one of the Easycap-type video grabbers and had been tearing my hair out trying unsuccessfully to get it to run on Windows 10. There are several different chipsets hiding under 'Easycap' exteriors and mine was one of the ones that is no longer supported by Windows.
Then I remembered that I'd installed some software on my old phone that had worked with 'most' USB webcams ... could there be something similar for Easycap devices? Answer yes! I found "USB Camera - Connect EasyCap or USB WebCam" by ShenYao China on the Play Store, installed it, plugged the Easycap in via a micro USB-USB2 adapter lead and hey presto! Pictures onscreen, and easily recorded!
I did a quick proof-of-concept capture from the FLIR Integrator 5/20 camera that I'm working on (it wasn't pointing at anything in particular, and was out of focus) but I was definitely able to view and record analogue video on my mobile phone's screen. Video is saved in MP4 format and plays fine on my Windows PC (and on the phone). Note that the black borders around the picture appear to be a feature of the camera - I saw the same effect when I connected the camera to a monitor.
The Easycap may be a bit of a battery-drainer but that doesn't worry me unduly as the Samsung Galaxy S7 supports charging via QI at the same time as the USB port is in use for OTG.
It's likely that there are other apps out there that can perform the same trick and drive an Easycap or similar USB dongle; the one I mention here is simply the one I tried first and as it worked there didn't seem to be any need to try others.
One final note: I connected video to the Easycap before connecting the Easycap to the phone. This seems to have made the app default correctly to PAL (25Hz), though sometimes it incorrectly selected composite input 2 rather than composite input 1 (which is where the camera was connected). Thankfully it's easy enough to select the 'Standard/Input' setting from the app's menu (3 vertical dots) and set it correctly.