Audio Sync: Editing & Rendering MPEG-2

nugent wrote on 12/3/2003, 12:54 PM

Using a Creative VideoBlaster MovieMaker, I have captured old PAL VHS video at 352x480, 25fps, 6Mbits/sec. Audio is 192 kbits/sec, 44.1 kHz. The capture encodes directly to MPEG-2.

I put the captured file on the Vegas (4.0c) timeline, and cut out some unwanted sections. The edited video plays just fine in Vegas.

I then rendered the project for use in a DVD, using the DVD Architect template for PAL. The audio was rendered separately as AC3.

When I pull the the resulting files into DVD Architect, the audio loses sychronization, until it is about two seconds behind the video. This is apparent in both the preview on the computer, and the burned DVD played on a standalone player.

I have tried rendering an MPEG-2 with sound and video together, but the result is the same. I have also tried PCM audio. If only a small section is rendered from the end of the project, the audio is in sync!

This issue has been discussed quite a bit on these forums, but I have not found a clear solution. So here's a hope that someone has found a solution?

Comments

Lawrence wrote on 12/3/2003, 2:39 PM

The old Creative VideoBlaster captured at D1/2 mpeg2.
For PAL, it's should be at 352x576, 25 fps.

The icompression chipset in VideoBlaster itself gives audiosync problem.

Try this workflow.

Rendering it to DV avi in V4. Do your editing,
Render final output to avi or direct to mpeg2.

Hope this helps.

MainConcept wrote on 12/3/2003, 5:35 PM

nugent wrote on 12/4/2003, 9:46 AM

Thanks for the responses so far.

Lawrence - you are correct, the capture was at 352x576. I am trying your workflow idea. However, this is slow, as I have to render the DV avi in sections due to 4GB limit in my Windows 98 SE. (I would be great! if Vegas could automatically split files) Then I have re-render to mpeg2 - renders take hours. Any comments on potential quality loss in this route?

Mr MainConcept, I am confused. I have been editing mpeg2 on Vegas. How is this different to what you propose? Anyway, sounds great to me!

johnmeyer wrote on 12/4/2003, 10:07 AM

MainConcept is thinking of developing an MPEG editing plug-in for Vegas. It would include full native editing, smart rendering, realtime performance at DVD resolution, HD support, etc. If this is something that would interest you, please post a comment.

Sign me up!

I have posted (probably too many times) why it is absolutely vital for Vegas to become completely conversant with MPEG. The summary of those comments is this: The final output for most projects is going to be DVD, and we are increasingly going to need to be able to re-author, re-purpose, and re-use these assets in future projects. Therefore, Vegas needs to be able to use MPEG directly.

Here are a few features that I would consider vital in such a plug-in or addition:

1. Should be able to easily handle VOB files. This is a key feature, because most people want to be able to take the VOBs directly from their own DVDs, and re-edit them. When a VOB is placed on the Vegas timeline, all audio streams associated with that VOB should be listed, and the user should be able to place any one of them on the timeline.

2. The ability to do cuts-only MPEG editing without recompression. Just as Vegas today does not "touch" the portions of a DV AVI file that are only cut (i.e., it does not recompress), this should also be done with MPEG. Obviously, if an edit is done in the middle of a GOP, the software will have to recompress a few frames around the edit point.

3. Should be able to handle AC3. Since Vegas encodes using AC3, and the goal here is to be able to re-use content that we have authored ourselves, you should make it easy to put the AC3 audio back into Vegas. Today, the only way I can use a VOB inside of Vegas is to first decode the audio back into a WAV file using a program like DVD2AVI. This is a needless, cumborsome step.

4. Should be able to seemlessly handle multiple MPEG files that have different compressions rates.

vonhosen wrote on 12/4/2003, 10:20 AM

Interested here as well.

People attempting to & experiencing problems ediitng MPEGs post on these forums quite regularly. Of course as with anything cost is what is going to play a major part in people's decision to go with the plug-in.

Fuzzy John wrote on 12/4/2003, 11:25 AM

Yes, Yes, Yes, Yes... Oh yesssssss...
Please count me in.

MainConcept wrote on 12/4/2003, 5:58 PM

1) Should be no problem, although we would have to leave copyright protection in place. Of course this would be no problem when you're capturing your own created VOBs.

2) Smart rendering will be included, working just that way.

3) We'll try to achieve that.

4) Yep. And the best part is that you can re-export MPEG files at different settings without actually re-encoding. For example if you import Sony MICROMV data and convert it to DVD-compliant MPEG-2, the data is simply requantized without being re-encoded (saving the quality loss that you would get with another generation).

Mark

nugent wrote on 12/8/2003, 6:22 AM

A follow-up: I rendered my edited project to DV avi. I had to do this in segments, because of the 4 GB limit in my 98SE. The avi's were then re-rendered to a single mpeg-2, the audio to ac3. This project had all audio in synch, except where the very orginal mpg had been cut and joined, creating a overlap on the audio.

A better method will be to convert the orginal mpg to avi before editing, and then proceed normally.

The conclusion is that editing mpeg-2 is not really feasible (yet). Thanks to those who made suggestions.

donp wrote on 12/8/2003, 6:46 AM

I normally do not edit MPEG-2. Do all my work on AVI files. A project recently
Came to me as as a Widows Media file but I talked the fellow who furnished it into giving me the original MiniDV tapes. However I would have tried to edit the MPEG if I could have so I support Mainconcept in creating the MPEG plugin, I havn't seen anything from Sony/Vegas on this thread. How do they feel about this since it is really their puppy.