Program to cut and sync audio tracks

[Bobdeluxe]

Hey there,

I want to sync a bunch of mkv files with audio files from another source.
The problem is that I need to cut and shift the audio files at certain points of the video.
In particular after the intro of an episode and sometimes after a few seconds of black screen in the video.
So I'm looking for a (preferably free) program where I can visually see how to cut and sync the audio file, with no or little quality loss.

Video format: HEVC
Audio format: AC-3

[ProWo]

Synch first and cut then the synched video.

For the cuts you can use avidemux (free).
It only cuts on keyframes.

[Bobdeluxe]

Correct me if I'm wrong, but it seems avidemux is not the right tool for what I'm trying to do.

To be more specific, I don't want to change anything about the video file. I only want to change the audio file.
The first 2 min of the video and audio file are in sync. I then need to cut the audio file and give it about 2000ms delay. I have to do this a few times.
I then want to render only the audio file and multiplex it with mkvtoolnix.

[ProWo]

Let's assume you have
- movie a with hevc video and ac3 audio.
- audio b (ac3) from another source.

Then:
extract audio from a as ac3 file.

Load audio a and audio b in audacity and match the tracks from b to a.

Then delete audio a from audacity and save b.

Then mux the hevc video track from a with b.

[Bobdeluxe]

Thanks! That will work.
Although a little bit more tedious than I was hoping for.