Is your feature request related to a problem? Please describe.
GoPro likes to chop up long videos to multiple files (4G/10G, depending on version).
Due to this using this tool will result in "broken" graphs, maps, etc.

Describe the solution you'd like
Add the option to specify multiple input videos.
For "easy" implementation (or POC):

• export GPX (as you are doing now)
• combine the GPX files somehow
• concat the videos using ffmpeg (I get that it will use double storage, but its easy)
• render the result

Describe alternatives you've considered
Manually exporting the GPX data, combining them, doing the concat manually and specifying the video/data manually:

• export: https://goprotelemetryextractor.com/free/#
• combine: https://gotoes.org/strava/Combine_GPX_TCX_FIT_Files.php

Not sure how big this request is in the grand scheme of things, but it would be a good-to-have.