I would love to have an external controller for start/stop/fast forward/rewind when watching tutorials on Youtube. For example a controller [1] people are using to edit videos. Quite often I would like to pause the video for a while, repeat last 30 sec or by-pass some boring segment.
I hesitate to mention mpv a second time in the same thread, but using mpv should make this fairly easy. You can control mpv over a unix socket, which should allow you to implement nearly any custom control scheme you can think of.
It's doable as an extension that communicates with a native program. There are already such extensions for media buttons, you might want to look among them―some may allow you to reconfigure the keys. Search for ‘media keys’ in the extension store.
However, rewinding is probably not among standard functionality of these extensions.
[1] https://www.amazon.com/Contour-Design-Shuttle-Xpress-Multime...