bad VHS to VCD transfer??

[Anonymous65]

I have a couple of poor quality VHS tapes where I loose audio sync after just 30 seconds of recording. Obviously, when watching the tape on TV the audio is in sync.

This is what I have tried so far:
Capture like normal where the video stream is locked to the audio stream. I don't loose frames during capture, but the audio is 5 seconds off after 20 minutes.

Capture with the audio and video streams running free (not locked to each other). Strangely, this gives the exact same audio sync problem!

Capture setting the frame rate at 29 or 31 frames per second. No change in the audio sync problem.

What gives??? Any ideas?
I have been thinking of using Tmpeg to get the frame rate back to 29.97, but the audio sync is still the same after the conversion to VCD. My guess the audio goes out of sync is because the frame rate is not 29.97, and when playing the AVI file (and perhaps when capturing) the player forces 29.97 frames per second. However, in Tmpeg, if there is a missing frame, it should add the previous frame to make up for the lost frame, and drop a frame if there are more than 2997 frames per second. Any way to make the audio stream and video stream follow each other no matter the frame rate?

SK

[Anonymous65]

Oh, let me add a few more things.
If I make a copy of the video tape and run the video through a TBC (Time Base Corrector), I see no reason why the tape should not digitize like normal and the audio stay in sync. However, why can't the PC make this time base correction to the video after capture, or even during capture? Anybody knowing the how the mpeg encoders work should be able to explain why, and how to achieve a new frame rate for bad video?

[rickmccl]

You're confusing me you capture _certain_ videotapes and get audio sync problem.

I have fixed out-of-sync avi files, but they were not my capture. I used *Virtual Dub*. there is a framerate conversion selection called 'match audio and video lengths' so it automatically determines a framerate that will cause the time length of the video to equal the time length of the audio. it will pick something weird-looking like maybe 29.5 FPS. If the number it picks is still 29.97, then you know it will not work

Why is your capture having problems? did you try different codecs to see if the video was just getting stopped up like an old toilet?

[Anonymous65]

The problem is the video tape. Is is a third generation tape with drop-outs, where the image is totally gone for as much as a second, and bad tracking errors that were recorded on the tape. I had the same kind of problem on a tape that had tons of edit points, where each edit was a glitch, and not a clean switch. The capture program tried both Vdub and Vcap32 just will not work correctly with such a bad video source.

One solution, a bit expensive, is to get a VCR with a built-in TBC. It should output clean frames at 29.97 no matter if I'm playing back noise on the tape or good video. The output video is always 29.97 frames per second.

But, I should try the feature in Tmpeg to match both the video and audio track. However, both tracks should be the same lenght to start with... I might have to get a TBC to be able to digitize bad video tapes.

[Anonymous65]

I got hold of a TBC and ran the video through it. I can now capture without any audio sync problems. So, I guess a VCR with a built-in TBC is very helpful when capturing from poor quality VHS tapes. It makes all the difference when it comes to audio sync problems (and at the same time cleans up the picture a bit)

SK

what is a TBC

[/quote]

[wet8092]

So can you dub the poor quality VHS tape to a good quality tape and then capture?

[Anonymous65]

TBC, time base corrector, forces new sync pulses on the video so it becomes a stable signal. It basically puts the video frames into memory, and then clock it out at a precise speed. This way you can capture really bad video tapes without having the capture card loose signal and loose audio sync. The cheapest way is to get a VCR with a built in TBC (like the JVC-S7800U for $300), or use an external TBC or PCI bus TBC (Videodata TBC-100 and TBC-1000, $300 and $200).