Is there a way to loop part of a video on macOS?

I'm trying to learn a language from a video. For this I would like to loop part of a video indefinitely, and additionally be able to change the speed of the video while it's playing back. Is there any way to loop part of a video like this on macOS? The simplest way I can think of is by trimming the video with ffmpeg or QuickTime Player, but that would become quite cumbersome with multiple parts of the video. There's also an online service called Looptube which does that that I've been using (for YouTube videos), but it's quite buggy and doesn't work at all half the time, so I've given up using it.