If the "usual route" is an ATI capture card, I can vouch for the fact that you can have these problems. If you capture via 1394 via your camcorder or a DV encoder, I would be surprised if you could get this sync problem. Did you capture via a DV encoder?

Sorry John:

VHS Player - Sony DV Cam (A - D converter) then fire wire using Sony Video Capture 5.0

Andy

If your usual 'route' is using a video card and the sound card....that's probably your problem. If you're using 1394 (firewire-like a canopus or similar) it should be fine. (if you can drag the audio track away from the video track and they're not 'locked' together, you have a problem.) But also note, if you did use 1394 and you made some cut's in the video, you could lose sync, but it usually takes about 20-30 minutes before you can notice it. (at least that's been my experience.) If you're not in sync, you can still separate the video from the audio and drag one track or the other back in sync, although you may end up jerry-rigging the whole thing together again. (using 'time-stretch' to compress or stretch the video back in sync) I also suggest using smpte time code on your time line. (preferences) (two messages appeared while I was writing this one.)

Steve:

So this audio drift is normal?

I'm annoyed it's so pronounced.

Andy

I wouldn't say it's normal. It depends on how it's put together and I've only had a few experiences where sometimes it stays perfectly in sync for an hour and a half and sometimes (I think due to editing) it slips, but my experience for my worst case senario was when my time code was not SMPTE (somehow switched by accident). I had some problems once, because I used two camera's and due to tape changes and accidental stoppages, I had to use the sound of one camera or the other and that created problems. I think in time, I'll figure out what causes what, but it's still too early for me to be sure exactly what creates the problem. Once it loses sync and you can drag one track away from the other (video and audio) that's when you start to jerry-rig. Sometimes you can re-render one song at a time back in sync or like I did, 'time-stretch' like a madman (making splits in the video track only and fixing each song.) I had to render one DVD 9 times before I got it in sync all the way to the end. (1 hour and 23 minutes in length)

Let me add this. Did it look in sync when you were transfering it? If it did, then make sure your time code, in preferences, is SMPTE (I use non-drop29.970, but I've seen arguments on this.) and drop the .avi back in the timeline and see if it plays in sync. Also be sure that the video and audio track are locked together. (If you try to drag the audio track away, the video should stick with it.) 1394 usually automatically locks these together. If they're not locked together then I'm at a loss for words.

The sample clocks in all digital recording devices are crystal controlled, however, this does not mean that all digital recording devices sample at exactly the same speed. Crystal controlled clocks are very stable and won't drift over the short term, but that doesn't mean that they are operating at the correct frequency to begin with.

Using an analog video capture card, like an ATI, coupled with recording the audio via a separate soundcard has an inherent problem. The video capture card and the soundcard have independent clocks and they will drift over time. Guaranteed. Now, there are two ways that a capture application can compensate for this disparity. It can adjust the video frame rate to match the audio, or the other way around. Neither soulution works completely. NTSC video is 29.97002997 frames per second and the audio is sampled at a rate of 48khz. This is the rate at which Vegas is going to play it back. If it wasn't recorded at exactly these rates, then something's going to drift.

DV camcorders and converters like the ADVC-100 synchronize the audio sample rate to the video, so they really can't drift. In the case of "locked audio", they can't drift at all. In the case of "unlocked audio", they can never drift enough to be noticable.

(for more on Locked vs Unlocked audio, read this).

As far as using two cameras on a shoot; in the pro world, they "genlock" the cameras so they are all operating off of the same clock. Consumer and prosumer DV camcorders have no provisions for genlocking. Each camera runs at its own rate but, if you're lucky, they will stay in sync for more than a few minutes at a time. You will probably have better luck if the two cameras are identical. Your chances of successfully mixing, let's say, a Sony and a Canon, for example, is probably even less likely to stay in sync over a long period of time. Pretty much any two (or more) DV cameras can be made to sync up if the shots are pretty short.

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TheGr8Steve, what do you mean when you say that the time code was "not SMPTE." Strictly speaking, the timecode of DV video isn't SMPTE anyway. But did you mean it wasn't set for Drop Frame when it should have been? There is no difference in the actual video frame rate between drop-frame and non-drop-frame, just the way the frame counter is incremented is different. Setting it to DF or NDF isn't going to affect the actual playback rate.

Another thing to keep in mind when using the audio from two different cameras to sync up the cameras is that sound travels at approximately one foot per millisecond through air. If you were using the camera mics and one camera was close to the sound source and the other was, let's say, 33 feet from the sound source, then, if you line up the audio waveforms in Vegas, your sync is already 1 frame off because there are 33 milliseconds in one frame of video. If both cameras are being fed from the same audio source, then this isn't a problem. Anyway, you need to be aware of this and compensate accordingly.

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Wolfbass, in the case of VHS to DV encoding, if the VHS tape has dropouts or is otherwise unstable, it will occasionally lose video sync and the video encoder in the DV camcorder may stop for a moment, while the audio will probably continue on its merry way. A timebase corrector (TBC) will really help in the transfer process and help to maintain audio/video sync.

John

As far as me using the SMPTE thing, I hardly remember what made me go to that. I just know that I had a video tape of me and a friend jamming on guitars and I decided to add some Bass and drums, afterwards. The new tracks would not stay in sync with the original video until I changed the timeline to SMPTE, and as soon as I discovered that, I never bothered trying any of the other tmecode settings. I know you're going to say that isn't what SMPTE is all about, I just know that it started staying in sync after I made that change and that was good enough for me. ( I can't explain how crazy it drives me, when I add more tracks, playing along with the video and then when I play them back, after re-syncing the beginning, they completely drift apart soon after starting playback. To you experienced users, this appears to be normal, to me it appears to be broken and I have to figure out how to fix it. Not exactly explained in the manual.)
I had also taken my Dig 8 and Hi8 cameras and filmed jams, with nobody operating the cameras, they were just on and then I mixed them in Vegas and they stayed perfectly sync'd for the duration of the Sony Dig8 tape. (no cuts, just camera switching and I used SMPTE non-drop )
Now just a couple of months ago, I had 3 shows I recorded, of live bands on the same day. I wish I could say I had recorded the sound separately with decent mics, but that wasn't an option that day. One camera was a Sony Dig8 and the other was a Hi 8 Canon. The Sony I used for both close ups and far away shots. When ever I got close up, the sound distorted so much it was unusable. But I was able to use the sound from the Canon Hi8. The first show was captured non-stop and both cameras stayed in sync for the duration of the first show. I was able to use the distorted sound from the Sony to sync it up with the sound of the Canon and they did not drift apart. I understand the difference in distance and sound travel, that wasn't the problem. The second show, I had to completely change my positions and both camera's were stopped and started and I had to literally patch the audio from both cameras into one long stream. When I say patched together, I didn't put it all on one track, I kept both cameras on their own tracks during mix-down and just placed them on the timeline where I needed them, turning which ever camera sounded better up at the right point. This worked pretty well, but at about 25 minutes in, the video and audio started drifting apart. This did not seem to happen right away, but a couple of weeks in, after tweaking this and that (video tweaks).(also discovered ruler had somehow changed to 'Time & Frames') This is where I started making cuts into the video track and stretching or compressing it to get back in sync. For this show, that worked. The 3rd show was similar to the second show in that both cameras had start and stop points and the sound had to be patched together, again the video and audio started drifting at about 25 minutes in. This time, the strange thing that happened is that it was in sync perfectly when I watched it on the timeline, but when I rendered it out to mpg2 and ac3, it would start to drift at about the 25 to 30 minute mark. I ended up with 3 mpgs stitched together and you can still see it start to lose sync just before the each mpg is through. It was while working on these 3 shows, that I discovered this forum. It didn't make sense to me, that this was happening. And in fact, you still won't be able to answer this because I never got answers that were consistant. I just ended up jerry-rigging the whole thing together and it's good enough, unless you get out the magnifying glass and really look at the last couple of minutes before each mpg ends. Yes, I know in reality that SMPTE is some code that professional cameras and some audio recorders use. It was just something that appeared to work for me. Especially when I added additional audio w/video to the original video recording. (I should point out that I had the audio from the Bass or drums, going into my soundcard (via RCA jacks), and also had the 1394 input from camera, at the same time. The 1394 being built into the Audigy Plat 2, which I've already heard is a lousy card.) The SMPTE non-drop setting fixed the drifting and I don't know why. This occured long before I discovered this forum.
Now explain to me how a video can look completely in sync while viewing it in the timeline and go out of sync when rendering mpg2 and ac3, using the exact start and stop point for both? I was able to play almost an hour and a half in timeline with no problem, but ended up having to make 3 separate mpgs, and I didn't have to re-sync anything, just render the .avi in 3 sections. (I think I asked about this here, and knew I wasn't going to get an answer.)

Steve:

The preferences for SMPTE: Are they in Vegas or Vid Cap?

Andy

Just a few tips and tricks I've picked up along the way but first let me say I've never had a sync drift problem but then again I'm in PAL land so this whole 'dropped frame' thing is a bit alien but as has been said I cannot see how it'd be an issue. I've captured 100s of hours of VHS via ADVC-300 and D8 camcorder prior to that and never had a problem.

Firstly as has been pointed out on a multicamer shoot you will have issues, withour genlock both audio and video will drift. There's some expensive gizmos to address this but you still need cameras with external sync inputs. However as I understand the issue with audio you can still have problems. The problem is the sample clock, even by design not all cameras run these at precisely 48.000KHz, the XL! was off by more than the Sony cameras to really cause havoc.

My best advice for avoiding these issues and maybe others might think this an uneeded set and I cannot really verify just how valid it as as I've never had to face these issues. Before you start editing, check all the syncs. Line everything up at the start on the one TL, then check the sync at the end. This is why lots of old hand slate the heads and tails of every shot. Once everything is in sync, render each A/V track out to a new file. Everything in all this files will now be 100% in sync.
Now when you're editing if things start getting out of whack you know it isn't becuase they were our to start with. With Ripple Edit exhibiting such odd behaviour it's easy enough to get things out even if they were right to start with.

Bob.