Some time ago there was talk about OpenTimelineIO, but I can no longer find the reference. What I was thinking of, was to use Audio Offset Finder to see the gap between files and then manually impose a timecode on each asset via the appropriate "set timecode" button. At this point you can use your "sync up" (i.e., "Align Timecodes") button whenever you want. Regarding the ease of losing sync on the timeline and then having to redo it again and again, I seem to remember that it was not possible to lock audio and video together because it meant creating a new type of "A/V" track while CinGG only has "A" and "V". In contrast to what you said, in my opinion, what all open NLEs on linux lack is synchronization in pre-editing, that is, in the Resources window, working even on dozens and dozens of sources. What is also missing is the ability to automatically replace, in each source, the embedded audio track with an external audio track. But always in pre-editing, not on the timeline. In my opinion, the operations of pre-editing should be present in an NLE, while post-editing may be missing.