Audio/Video sync issues after rendering

MusicTECH wrote on 5/2/2003, 1:45 PM
I've been working on some short video clips in highly compressed mpeg-1 format that will be used on an Enhanced CD (mostly music, with some multimedia stuff in the second session).

I captured the clips directly from my mini-DV camera, and did all the editing and audio sweetening in VV4 and rendered to an AVI file.

I then start a new project and open up the AVI file on its own. Audio/Video sync is perfect in the AVI version. I then try to render this as an MPEG-1 in a small multimedia format for computer, and when I play back the resulting mpg file, the audio and video drift apart fairly quickly. Most of the clips are only around 5 minutes long, but you can already tell by the end of those that the audio/video is not synchronized. Then, there is one clips that's a bit over 12 minutes long, and by the end of that clip, the audio and video are at least 1 full second apart!

This is definitely not acceptable!

I've played around with the render settings, encoding audio at different bit rates and at both 44.1Khz and 48 Khz, and I get pretty much the same results every time.

Usually I just do stuff for DVD and have not had any problems with MPEG-2 renders, but I do recall sometime last year I did a short concert clip (around 6 minutes) in Vegas 3 that I rendered to Real Vido for the web, and the audio/video drifted out of sync with that clip as well.

Is this a Vegas problem? Or is it a problem with highly compressed video/audio formats in general?

Does anyone have a solution?

I need to wrap up this current product to get it into manufacturing as soon as possible, and this is a MAJOR show-stopper right now!

Thanks in advance for any help.

Stephen Sherrard

Comments

pconti wrote on 5/2/2003, 2:15 PM
I have seen that MPEG-2 files drift apart over time after rendering. However, I'm using DVDa so when I render for that application I make the MPEG-2 file using the DVDa template and the audio is a separate AC-3 file. The resulting DVD's are fine.

I posted on this issue a while ago and have seen several others like yourself post on it too. I haven't seen a response from SOFO though.
Frenchy wrote on 5/2/2003, 3:45 PM
MusicTech:
How are you playing back the mpeg - on your pc? - If so, I've had similar problems, something about the pc not able to keep up decoding the vid and playing audio from mpeg's very well. Maybe a higher compression makes this more pronounced. Playing mpeg's (VCD or SVCD) on standalone DVD players is flawless, as it is with avi's(either from cammy, or copied to VHS). I've not had any problems with wmv files either. In short, Vegas has been a godsend with regards to prior (constant) audio synch problems with MGI's videwave shit. Good luck

Frenchy
MusicTECH wrote on 5/2/2003, 5:15 PM
OK... figured it out! Just a little brain fart.

When I switched the template from VCD to MPEG-1 and started making adjustments, somehow the framerate got set to 30fps. The original AVIs are at 29.97 ND, so those 0.03 frames each second were adding up and causing the video/audio to drift. When I set it back to 29.97 fps, the sync was perfect in the resulting mpg file.

So, I guess that means you can't Render at a different frame rate than the original clip? Not that I need to for this project, but how would you do that if you wanted to? Is there a way to resample the audio/video together if you wanted to say convert an NTSC video to PAL? Or, simply go to a lower frame rate to make the file size smaller for internet stuff?

Just curious. I'm a music producer and audio engineer and am just starting to get into this video stuff more seriously, so I'm learning as I go.

Thanks.

Steve