Ask HN: Options for single-button media remote control for smartphones?

I'm going through a Language Transfer course [1] and it requires pausing lesson after Mihalis asks a question and before his minion gets a chance to answer it.

I'd like to go through the course while running, so looking for a simple one-button remote control for the phone that can pause/resume the playback.

There are some shutter controls of this sort for taking selfies, but they don't seem to be re-programmable for media control.

Are there any ready-made options for this?

[1] https://www.languagetransfer.org