Relevant links:
Virtualdub video editor: http://virtualdub.sourceforge.net/ (get 64-bit version unless you're still on a 32 bit system for some reason)
VIrtualDub FFMPEG input plugin: https://codecpack.co/download/FFInputDriver.html (dead original link: https://sourceforge.net/projects/virtualdubffmpeginputplugin/ )
Unzip VirtualDub program. Open the plugin zip and copy the contents of the plugins64 folder to the folder of the same name in your unzipped VirtualDub folder. (if that doesn't make sense, watch the video, it shows exactly what to do!)