The symptom: Your converted video begins with the sound and picture in sync. But over the course of the video, the audio and video slowly drift out of sync. The longer the file, the more out of sync the video and audio will be towards the end.

This is a very common problem and is usually the result of converting an MPEG4-based AVI file to a Mac-friendly video format.

Theres little I hate more than watching a video where the sound doesnt match up with the mouths of the characters (especially when Ive spent hours downloading or converting said AVI files). Im here to offer a dirty, trial-and-error fix for this annoying predicament, but youll need QuickTime Pro and a little patience to do it.
You can download some useful software form here

Putting the Sound in Sync

Open your out-of-sync iPod video in QuickTime. Select Window: Show Movie Info and remember the FPS (frames per second) number. Close the info window.

Move the play head toward the end of the video and press play. Estimate how out of sync the audio is towards the end of the movie. Is it a second? Is it less than a second? If the words and audio are only slightly out of sync, youre probably looking at less than half a second.

Now, select Edit: Select All. Your timeline is now completely selected. There are two handles on your timeline, one at the start of your movie and one at the end. Select the one at the end (it should turn black) and drag it all the way to the right to ensure that it is at the very end of the timeline.

Were going to chop off a tiny part at the end of our movie in order to re-sync the audio with the video.

Use your left arrow key and count the taps it takes until the counter on the left goes down to the previous second. Each tap of the left arrow key rewinds one frame of video. How many taps did it take? Was it close to the FPS number? If it was, that means we just rewound nearly a full second of video. Tap the left arrow key until youve rewound the video to your estimate. Dont worry; you dont need to be exact. Just remember the number of taps you made and maybe write it down somewhere. Unless your audio is horribly out of sync, youre probably not going to want to rewind more than 5 or 6 frames to begin with.

Okay, now select Edit: Copy, then Edit: Select All, then Edit: Add to selection & scale. Now, select Window: Show Movie Properties. You should see two video tracks and two sound tracks. Video Track 1 and Sound Track 1 are the original tracks. The second tracks are the slightly shortened tracks. Now, were going to mix-and-match using the check boxes to find out if we got closer to matching the audio and video.

When you begin, all four tracks will be selected.

Move the playhead to a point later in the movie and press play. Mix and match tracks labeled 1′ with tracks labeled 2′ selecting only one Video Track and one Sound Track at a time.

Play Video Track 1 with Sound Track 2 and then try playing Video Track 2 with Sound Track 1. One of these options should be much better than the other. If you hit the sweet spot and the audio and video are matched up, delete the unselected tracks and select File: Save and make sure you select self contained movie. Your new QuickTime movies audio is now synced and its all ready for your iPod.

if the audio and video match up, delete the unselected tracks.

If one of the selections is only somewhat better than the original, close the file without saving it. When you reopen your original file, repeat the steps above, but youll tap the left arrow key a few more times than you did previously. A good rule of thumb is to progressively add five more frames than you entered previously.

Again select all, copy, add to selection and mix-and-match the tracks to see if youve come any closer.

If neither pairing is better than the way the original video was, you overshot the number of frames to trim. Repeat the process, but lower the number of frames that you tap with the left arrow key.

Above is a method to fix the sync problem. If you have any other iPod problems, you can refer here for more help.
I wish it is useful to you; enjoy your favorite videos on iPod anytime and anywhere. :wavey: