I've had some very large high-bitrate files that will play choppy on a laptop HDD because they're 5400RPM and they can barely get the data off and through the SATA port quick enough. Playing them across the mess that is USB just wasn't a thing that would work.
Also had files that were just encoded like shit. It's hard to tell what you get sometimes when you find them laying around on the Internet.
You should try MPV or VLC (they handle hardware decoding) and have a pretty good caching system.
Vlc is the only thing I've used for like, 13 years.
I use VLC. Even it has issues with some things I've acquired.
Try MPV. It could also be that your videos might be encoded in h.265, which looks like shit if your CPU and GPU aren't fast enough to decode the stream.
The files on the laptop hd played fine until I copied them to the external. now the files in both places are shit.
That's odd. I can't offer an explanation unless your drive is failing or highly fragmented.
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