Last time I checked best choices for Windows 9x were MediaPlayerClassic 6.4.9.1 https://sourceforge.net/projects/guliverkli2/ … lassic/6.4.9.1/) and PotPlayer for Windows XP (MPC-HC was also good https://github.com/mpc-hc/mpc-hc). But I'm no longer interested in watching movies on vintage computers, so I may not be up to date...

I remember that in the past I switched to PotPlayer because it supported DXVA offered by graphics cards (and was more handy - everything I needed was in the context menu).

Of things that come to mind to point out, PotPlayer has its own codecs and supports loading external codecs, can add similar named files to playlist automatically, can open YouTube links and allows selection of codec for videos from YouTube, can use madVR video renderer, a thumbnail popup of video at specific time can be enabled when hovering over navigation bar, the thumbnail can show the chapter if available, has a dialog for configuring decoders for different codecs (you could use CUDA on NVIDIA hardware instead of DXVA), its D3D renderers support exclusive mode.

The part handling YouTube is external programmable Lua module, can be edited and it's possible to add support for some other site if you find a third party module.

Personally I don't consider PotPlayer great with just vintage PCs and you'll have to look for old version if you want to run it on Windows XP. CUDA is useful there, at least I couldn't combine DXVA with madVR, but that's XP.

Mplayer has windows builds too. It’s a huge statically linked exe onto which you can drag any video file and it plays. You can also invoke the usual command line options like skiploopfilter etc to speed up decoding on slow stuff.