Audio and Video Mismatch

Peyton-Todd wrote on 7/15/2005, 11:04 AM
Can anyone explain what's wrong here? Do the latest versions of Vegas fix it?

I have Vegas 3.0. Whenever I convert an AVI to MPEG1 using MainConcept's codec which shipped with Vegas, then try to convert that to a Quicktime MOV file, then load that back into Vegas, I find that the Audio track is longer than the Video. (Usually, it has been exactly two frames longer, but I just tried it again and found it to be 3.5 frames longer - that's right, not an integral number.)

Yes, I know I can just go back to the original AVI files work from there, but I have hundreds of MPEG clips made in the way described, and only recently decided to convert them to MOV. I would have to do all that work over again.

Any ideas?

Thanks,
Peyton Todd

Comments

Chienworks wrote on 7/15/2005, 11:24 AM
My guess is that the difference may be due to GOP (group of pictures) differences between MPEG and QuickTime. Whatever software you use to convert to MOV may be padding out the length to include a full GOP, even if the last few frames are blank.

I'm not sure why it would be all that much more work to use Vegas to make MOV files from your original AVI files than i would be to convert MPEG to MOV. In any case you're probably going to take a substantial quality hit converting from MPEG to MOV, and it may be taking a lot longer than if you started with AVI again.
Peyton-Todd wrote on 7/15/2005, 12:01 PM
Actually, you'd be astounded at how little quality is lost. Perhaps that's partly because the quality was never wonderful to begin with, given that the originals were reel-to-reel black and white made 35 years ago. Secondly, the MainConcept codec appears to be a very good one - I notice no deterioration of quality at all going from AVI to these MPEG1 files. Thirdly, the MOV screen size I'm making is much smaller. And again, I notice no deterioration in quality going from the MPEG1s to MOV. Truly, the only problem is the lack of sync between the video and audio.

Does anyone with 3.0 have the same problem? Does anyone with later versions of Vegas encounter it? If it's fixed now, I might be willing to pay the upgrade price.
Former user wrote on 7/15/2005, 1:56 PM
Is this causing problems with the file?

Dave T2
Peyton-Todd wrote on 7/15/2005, 2:42 PM
Believe it or not, Dave, the answer may be No.

In previous experiences involving conversion of Vegas-produced MPEG1 files into MP4 via Quicktime, the MP4 result shows in Quicktime with a blank white screen at the end, where the extra portion of audio is.

But with the procedure I'm describing here - doing it all within Vegas - Quicktime stops at the end of the video as it should, and does not display the extra video-less frames. So MAYBE there's no problem after all, in practical terms.

What's really strange is that, if you put the Vegas-created MOV file into Vegas and try to chop off the video-less audio frames at the end, rendering the result as MOV, Vegas put the extra frames back onto it. In fact, on my first attempt, it added STILL MORE frames, taking it, in this case, from one extra frame to 2.5 extra frames. However, on subsequent iterations, it merely put back what was there, never going beyond 2.5 frames.

Also - a quirk I wonder how to explain - the quality deteriorated slightly with each next reproduction, even though I was rendering MOV as MOV.

Another point: So far, all the extra audio frames as the end have been silence - and most of my clips are so short that I do not perceive any lack of sync between voice and picture. So again, maybe it's a problem which isn't a problem. I hope so. But it would be nice to understand it better - maybe something do with the GOP problem suggested by another responder?
Chienworks wrote on 7/15/2005, 4:42 PM
Rendering MOV to MOV will degrade quality if you are using compressed formats. The video must be decompressed and then recompressed when rendering.