I'm processing some files that I transferred from video tape via ElGato video capture device. This one is a large mp4 file (mp4 is the default output from the ElGato) which, as usual using this device, has a problem synching the audio and video. (Note that subsequent to capturing this video, I have found that I can get an intermediate video file made by ElGato, a .ts file, that does not have the synch problem. The catch is that I have to find that file before ElGato saves the mp4 because the .ts file is autodeleted once the mp4 is saved. However, for this case, I have only the mp4.) I'm having a problem synching the audio and video for one particular segment of my sequence.
The method I use to try to synch the video and audio is to unlink the audio and video clips; then create gaps before and after the clips so there is room to move them around without overlapping other clips in the sequence; drag the audio or video clip until I feel the clips are properly synched; finally group the clips to keep them synched up.
This method has worked fine for me several times. In fact, after I started having the problem described below, I tried the same method on a clip farther on in the sequence, and it worked fine.
Moving on to the problem. I proceed as described above, but when I drag the audio and drop it, the entire video clip ends up being moved all the way to the end of the audio clip. Ctrl-Z puts everything back the way it was. Moving the video has the same effect, although in this case the audio may end up at the end of the video. I also noticed during this process that the audio clip has a strange little split part way through. When I select the audio clip, it shows highlighted, but there is a short gap part way through that is not highlighted. The waveform in that gap looks like it drops to zero volume, but when I play it, I hear sound continuously. The rest of the audio clip beyond the gap is highlighted. If I hover over any of the three pieces, the properties that are shown (such as duration of the audio) are the same for all three of these pieces.
A really frustrating part of this is that I had the audio and video synched for this clip at one point, but somehow, even though I had the audio and video clips grouped, when I changed something earlier in the sequence, it knocked the audio and video out of synch in this part.
You can see a video that demonstrates some of this here:
https://www.dropbox.com/s/m3fcdohysfdqd4l/VID00002.MP4?dl=0