Audio Video Sync

[amitray]

I have 2 video files of an event one with good video but bad audio and another with bad video but good audio. I was able to separate video and audio from both the files. I wanted to combine the good video and good audio. There is no proper syncing as there is a 3 seconds lag in good audio. How can I sync the video with audio? I just need to start audio after 3 seconds of video being played. Is there any tutorial on this?

[hello_hello]

MKVToolNixGUI. It'll open many file formats. Open one of the files and add the second (no need to extracted the streams first in most cases), select the video and audio you want to keep, then re-multiplex as a new MKV. There's an option for setting a delay for any stream in ms (under the Timecodes tab), so you'd have to select the audio stream you're keeping in the "tracks chapters and tags" section and set it to roughly 3000 (positive or negative). If you need another output file type you'll need to use a different program, but I don't know what that might be.

[transporterfan]

Try using Audacity. Add three seconds of silence to the beginning of the track, save it off and mux it with the video.
Failing that, you will have to use an NLE (a video editor) and load the video and audio tracks in a timeline.
You can then move the audio track until you find the sync point. Examples on Youtube (search 'sync audio with video').