I would like to merge a video (visual) track in with an audio track from another source. However, there is a lack of a number of seconds and I will need to adjust the sound at several checkpoints throughout the movie. Not just in the beginning - which I've done in the past - not that hard. I have no previous experience - what tools are best for this purpose, and easiest to use for syncing visual with audio, for a film? The goal is to create a nice .mkv or possibly .avi file where the audio and video are matching. This is a matter of rescuing an old film.