Tape start position changes audio sync by seconds?

[semmelbroesel]

Hi.

I'm using VirtualDub 1.10.4 64bit version, the Diamond VC500 card, and Windows 8.1 64bit. I'm using Huffyuv video compression and no audio compression. The VCR is a JVC HR-S9700.

I just did some captures with a VCR I just bought, and it had maybe half a second of audio sync which I found somewhat acceptable for the moment.

Then I used a full 4 hour tape and found that I got a 2 second audio delay.

I kept trying different settings and went back to the tutorial here from the board.

What I eventually found out was this:

The tape has multiple TV recordings on it with some empty space in between (i.e. no recording on it - the space was skipped before adding the next recording). I started a bit before the second recording.

If I start capturing 10 seconds before the program starts, I get 8 seconds of audio lag. If I start capturing 5 seconds before the program starts, I get 4 seconds of audio lag. If I can cut it close enough to hit start 1 second before the program starts, audio appears to be reasonably synced.

During the capture process, the audio meter seemed to react to the audio CORRECTLY as it came in (i.e. when I knew the music started, the audio meters jumped accordingly) - and then I'd play the video file later and find these huge lags.

My questions:

1. Is it normal for empty tape space to mess up the audio sync so much? What could cause this?

2. Is there a way to avoid it?

3. Should I record the entire tape in one go from the beginning instead of starting 30 minutes in?

And a quick side question:

4. If I capture with Huffyuv, can I use VirtualDub to edit out parts I don't want with "Direct Stream Copy" and without any loss in quality of sync?

Thanks!

[msgohan]

This is expected when there is no device performing frame TBC in your capture chain.

[lollo2]

In addition to what msgohan said (main cause), you could:
- switch to VirtualDub 1.9.11
- capture each segment separatly
- try AmarecTV

Quote:

If I capture with Huffyuv, can I use VirtualDub to edit out parts I don't want with "Direct Stream Copy" and without any loss in quality of sync?

Yes (but check options in VirtualDUb -> Audio -> Interleaving...)

[semmelbroesel]

I figured it out, and it shouldn't have been this difficult if my brain wasn't so foggy these days that I don't spot the obvious...

"Sync video to audio by adjusting video timing" - that's all it took. (I also have drop and insert frames enabled, but the dropped frames count has been 0 since I changed the sync setting).

Makes sense - some of my videos contain music, so the audio should drive everything.

Now I can start over and get it done properly.

Thanks for all responses!