I’m being a bit lazy here. But I expect researching this would take a hell of a lot more time than just asking here.
Vidometer is an iOS-only app I’ve seen used in many ride videos. It places a speedometer, odometer, map, and even more (optional), over iPhone video footage of the ride being recorded.
Is there anything like that for Android? Or even for specific action cams?
Same-day update after the break.
Being impatient, I did some quick research and ran across this:
Add GPS Data Overlays to GoPro Video For Free!
But I’d still rather have an Android all-in-one app that does that. Preferably with 4K video recording too.
Right now, it seems I’d have to get an iPhone for this. And that’s a very expensive proposition, given the way Apple tiers pricing with a huge jump from 16GBs of storage (a laughable and almost-useless amount!) to 64 or 128GBs.
Of course, I could always go with an action cam, but that’s an entirely new level of research! I’m open to advice for them too.
Mike Cane's Atomic Supermen 
I have some good news.
iPhone SE, 6s, and 7 start at 32GB, +$100 for 128GB.
8 and X start at 64GB, +$150 for 256GB.
So, there are no more 16GB iPhones! Also, while iPhones get software updates for years, most android phones are never supported at all.
Huh. I haven’t Kept Up! Went to Apple to check the 6s price. US$449 for 32Gbs. Something new to think about. Thanks.