Attn: TugBoat. Fixing audio sync issues tutorial (AVI to DVD)

TugBoat,

I came across your instructions (and here) for fixing audio sync problems, but there's not enough detail for me to work with. I was hoping you can help clarify some of the steps.

I've got a bunch of AVIs with mp3 audio that go out of sync when I convert them to (S)VCD or CVD or DVD. The audio is in sync when played as AVIs using QT or VLC.

There seems to be two ways to fix the out of sync issue: 1) use SyncHole, QT Sync, or QT Mutator; 3) use Quicktime and ffmpegX (your method). Unfortunately, there aren't any clear, detailed newbie instructions for any of these applications. So I'm going with your method, but I need to clear up a few things.

And if anyone knows how to fix audio sync issues using SyncHole, QT Sync, or QT Mutator, could you please write a clear, newbie-friendly tutorial? Thank. Anyway, back to the issue at hand.

Tugboat wrote:

The easiest way to correct it is trial and error with QT Pros editing feature. Apparently that particular AVI was muxed with delay settings that don't get exported correctly when converting to separate tracks. Another possible cause is the Scale function you mentioned or Variable Bitrate Audio. You should never scale a track that is going to be separated from the track it's scaled to. And never use Variable Bitrate Audio in a movie.

I'd appreciate it if you could correct, complete, and elaborate on the instructions below which I culled from the post linked to above. Thanks.

Step 1: Open a copy of the AVI QuickTime, select 'Show Movie Info' and 'Show Movie Properties'.

Step 2: Extract the Audio track, then delete the Audio track from the movie.

Step 3: Then "export" the Audio track to AIFF (for Toast) or WAV (for ffmpegX). This will correct the variable bitrate errors.
What settings do I select for AIFF or WAV?

WAV: Rate (16 kHz or something else)? Linear PCM Settings? Sample size (16 bits or something else)? Little Endian enabled? Floating Point?

AIFF: Rate (48.000 kHz?) Render settings? Sample size? Why doesn't ffmpegX support AIFF?

Step 4: [I got lost here] Am I supposed to first convert the AIFF or WAV to MP3 or AC3 using ffmpegX or I can add the AIFF or WAV directly to the AVI and then do the conversion?

Step 5: Select all and copy on the Audio track and then Add it to the video track. DO NOT SCALE [what does "scale" do?].

Step 6: Scan the new movie and see how it is synced. If the Audio track is ahead, you need to either add content to the beginning of the audio track(?) or delete content from the beginning of the Video track. You can undo the 'Add to Movie', make the corrections, then 'Add to Movie' again. You can make the small selections with the triangles on the bottom of the QT timeline using the left and right arrow keys. The 'Show Movie Info' window will display the length of the selections as you use the arrow keys.

[How do you "add" content to the audio track?]

Once you have the beginning synced, check out the end. If the end is out of sync, then you need to use something like Final Cut Express, FCP, or some other App to 'Change the Duration' of the Audio track to match the duration of the Video track.

Step 7: Save the movie file [to .MOV?]. Then convert using Toast or ffmpegX.

Step 3: Then "export" the Audio track to AIFF (for Toast) or WAV (for ffmpegX). This will correct the variable bitrate errors.
What settings do I select for AIFF or WAV?

Well, you can choose whatever you wish. Since I always convert the Audio to AC3, using Compressor, I choose 48kHz, Better, 16. Once I have it synced, I convert the AIFF to AC3, then mux with D-Vision or Nandub (in VPC).

Step 4: [I got lost here] Am I supposed to first convert the AIFF or WAV to MP3 or AC3 using ffmpegX or I can add the AIFF or WAV directly to the AVI and then do the conversion?

You can do either, there are many ways to skin a cat. You cannot add an AC3 track to a Video with QT. You can save the Video track to an AVI by using the 'Export', 'Save as AVI' MPEG Streamclip plugin. Then you can use D-Vision (or Nandub in VPC) to mux the Video.AVI with the Audio.AC3.

Step 5: Select all and copy on the Audio track and then Add it to the video track. DO NOT SCALE [what does "scale" do?].

Scaling changes the duration of one track to match another track. This works fine as long as the two tracks are kept in the same wrapper. When the tracks are separated, they revert to their original durations which may not be in sync at their original durations.

Step 6: Scan the new movie and see how it is synced. If the Audio track is ahead, you need to either [u]add content to the beginning of the audio track[/](?) or delete content from the beginning of the Video track. You can undo the 'Add to Movie', make the corrections, then 'Add to Movie' again. You can make the small selections with the triangles on the bottom of the QT timeline using the left and right arrow keys. The 'Show Movie Info' window will display the length of the selections as you use the arrow keys.

[How do you "add" content to the audio track?]

You select an area of the Audio track that contains silence, such as the beginning or the end, copy, move the playhead back to the beginning of the track, then paste. Note that QT Player does non-precise audio editing. I think the smallest selection is .25 seconds. If you need more precision when editing, edit the Video track which allows more precise editing. Again, select a portion of the Video track that's black (the beginning), copy, move playhead back to beginning, paste. Most of the sync problems I've seen are round numbers, such as .5, 1, or 2 seconds in duration, as in, easy to fix by editing the Audio track. If I want precision when editing Audio, I use Peak instead of QT.

It's not a difficult procedure, and since I convert ALL my AVIs to AC3 audio, it's something I do often.

Tugboat,

Thanks for your help. I was able to fix the audio sync problem using your instructions.