it's not as hard as you're making it seem, you just allow for a positive or negative time offset and rely on the devices counting seconds similarly, which is mostly a given now.

I did this with raw footage and a VESC speed controller dump to overlay a bunch of motor stats on a prior project, this was pre-AI and it was still only an afternoon project.

ffmpeg/image-magick do all the real heavy lifting out of the box.

This sounds like something Claude Code could do very easily. If you need to actually look at the videos that's harder but still possible, but if it's just aligning GPS times and timestamps with reasonably accurate clocks, Claude Could probably do the ffmpeg commands unsupervised. I wouldn't be surprised if Haiku (the cheapest model) could do it, or an open-source agent harness with another small 30B model.

Just prompting claude (probably I would start with Opus) "I would like a HUD display of the following metrics from my Fit file overlayed on these GoPro videos, and I'd like the videos stitched together (there are some gaps, I want seamless playback) it would probably do it in 30 minutes or less, and the majority of the time would probably be ffmpeg.