All what you need to do and it is a pain, if you are using a PC, Windows 10 I am not sure about 7 anymore. You have a video editor that is built in to 10 by MicroGreed.
When I download something off YT I run it through that and drop the resolution down to 540p it still looks good even on a 4K 43 inch TV that I use for a monitor.
I think that there should be a way of downsizing videos automatically, there should be a program out there that will do it in batches.
It is a pain in the backside to have to do this at all, but as AM is such an amazing front end apart from this, then it is worth sticking to. If you are downloading from Emu Movies, then make sure that you download hi quality MP4 and not the HD versions, when I was using the HD version it was stutter all over the place.
Regards
Mark