I used the AverMedia Live Gamer Extreme (GC550), and for all the consoles I had, only Line2x was supported, which was good, but highly a shame as I wanted to record my favorite machines on at least a 720p resolution.
I now use an Elgato Cam Link, as advised by Vince, and it does work extremely well as I can now record on line3x and onward (even 5x, which is absolutely surprising for such a small device, ahah)
However, I have a major problem, when it comes to recording the SNES, and Nintendo 64 on Line3x/Line4x : when I try to do so, it has major & quick screen distorsions, and I don’t know how to fix them. Of course, I use the official SCART cable from the SNES. However, on Line2X, no problem.
In case of: My SNES is a PAL which has a SuperCIC installed, and my N64 is a NUS-FRA (thus, RGB modified).
Video showcasing the problem: https://twitter.com/Ch0wW7/status/943569166073819136
I recently bought Elgato Cam Link and had the same problem. After trying tweaking the settings I found a solution. Set “Allow TVP HPLL2x” On, and if the picture still jitters, set v.synclen to 7 and v.backporch to 10. This is for 3x mode.