Yep, I've done this too. I had a video with a live youtube transcript for a talk, but in addition I had a manually written transcript from one of the attendees. She wasn't trying to make it word-for-word perfect, but it was reasonably close and obviously had better formatting.

The automatic transcript was fairly poor quality but had fairly precise timestamps. The manual transcript lacked timestamps but was high quality. So I used an approximate matching algorithm to combine them and produce a clickable version of the manual transcript where every group of words was a direct link to that portion of the youtube video. It all worked out surprisingly well. (The other piece was that I hand-inserted annotations to produce an index of various topics and concepts that I thought were significant.)

I don't know how common of a situation this is, since it requires having a high-fidelity human-created transcript. I could clean up the tools and release them, I suppose. I did this for a birthday present.

(I don't have a demo because it's a private video, sadly, and I have rights to neither the video nor the manual transcript.)