So from a shooting / editing standpoint, here’s how do it.
You’ll definitely want to record audio separately. You can use something like an A139 Pro that offers an external wired lav mic, record to a mic wired to your phone that’s running to a wired mic, or get a mic that clips onto your chest and record it separately too.
Now for the editing, synicing video and audio is trivial. Most any reasonable video editor will have an option to do that for you.
Two things come to mind for the video.
First, some dashcams (and I don’t know about the A810 off the top of my head) don’t have perfect continuity between clips meaning there might be a tiny gap between subsequent clips and so you’ll have black frames in the video every minute or so for those gaps.
You can combine those clips into one big clip, but again if they’re not continuous then the video and audio are gonna get more and more out of sync as time goes on. For this reason you’ll want to ensure your dashcam perfectly transitions from one clip to the next.
When it comes to combining a bunch of video clips, you’ll want to see what method works best with your editor of choice. There’s a few approaches that come to mine:
-Merge the videos in something like LosslessCut then sync video and audio in your editor.
-Combine the video clips in your editor directly into a new clip and then sync that with your audio
-Layout all the video clips in your timeline, manually sync the audio, mute all the video clips, then combine into one synced clip.
Find the easiest approach when starting your edit and it’ll pay dividends when you start cutting for the actual edit.
Then when it comes to audio, some editors have options to reduce noise or isolate your voice audio.
Adobe also has a tool that helps clean up audio and make it sound like it was shot in a studio. It’s actually made for podcasts.
https://podcast.adobe.com/ I haven’t always been a huge fan of the results, but it does help in some instances and I wouldn’t be surprised if it’s gotten better since I first tried it. YMMV.
Finally if you do have to cut, try to do it without varying your car speed so that the road noise and engine noise sounds the same and the cut is less jarring and noticeable. Using cruise control will help. You can also switch the video between a front and interior cam, for example, to help visually hide the cut. Hiding the time (or just slightly zooming in in post to hide the clock) can also help mask any cuts you make.
Sounds like a fun project. I hope you have fun creating it!