Random audio/video sync problem with webcam recorded video

[TinoArts]

Hello, I am new here and I hope I am posting this to the right category.

Yesterday I recorded few videos, using Free2X Webcam Recorder tool and my Acer laptop built-in webcam. The format is .AVI, resolution is 720p and according to MediaInfo, the framerate is 23.976. I have 5 videos, some or 40 minutes long and the longest one is 2,5 hours long.

The problem is the video and audio are out of sync. I am not talking about the delay, which could be fixed by shifting the audio track by some amount of miliseconds. The sync goes out randomly, and I don't know how to fix it.

What I know:
- both audio and video tracks are of the same length. Basically, the first couple of seconds are ALWAYS synced, and the ending of the video is aleays quite all right as well (1s delay at most I think). However, most of the time of the playback, it is not synced at all.
- the first video has 40 minutes, the sync is perfect in the beginning, and it is sort of all right until the end. At the end, there is a delay of 1 second or even less. The video is watchable. On the other hand, the other video which is 2 hours long gets messed up in just couple of minutes. After three minutes of playback, the delay is more than 3 seconds. Then, in the middle, the delay is more than 20 seconds and it seems completely random.
- the video is kind of messed up, it is noticable because some parts seem speeded up 2 times or so, the speed is not constant (it is most of the time, but not always) - I believe it is some video lag which is causing this sync problem.

I already tried the Handbrake tool to convert it to the "constant framerate", no difference.

Fixing these videos is really important for me. Do I have any chance? Thank you.

EDIT: I've noticed every single video speeds up at some point before the end (4 minutes, 20 minutes, depends on the video length), probably to catch up with the audio track. However, the video lag/delay throughout the video doesn't seem to be constant, so I am not sure how to calculate what to do.

[davexnet]

Open one of the troublesome files in Mediainfo, put it in Text view and post the whole thing in your next reply

[Krispy Kritter]

Hardware specs would be helpful as well. If the laptop is under powered, or doing something else at the same time, it may not be capturing properly. In other words, the file(s) are possibly being created with sync issues.