Sony Vegas 6 Capture - audio sync problem
by Lance Placey
on
Jan 29, 2008 at 10:34:24 pm
I have Sony Vegas 6 with the latest update installed ( d ) from the sony site. I have an ATI All-in-wonder card ( ATI RAGE PRO chipset ) and a Soundmax sound card.
When capturing video from a VHS player, the video and audio appear to be in sync during the capture, but after the capture is complete, when I load the video to the editor, I find that the audio length is longer then the video length. Video and Audio appear to match fairly close at the begging of play, but toward the end appear to be further and further out of sync. It seems that this must be some sort of encoding issue on the audio track that seems to "stretch" the audio. Does anyone have any idea how I can correct the issue ?
Re: Sony Vegas 6 Capture - audio sync problem by Don Bloom on Jan 30, 2008 at 12:31:05 am
I have encourtered this a couple of times as well. The only way I could fix it was to find silent areas split the audio track and adjust as needed. It was a PITA but luckily there were enough areas of silence that I could split the track and move it.
Re: Sony Vegas 6 Capture - audio sync problem by Rick Mac on Jan 30, 2008 at 4:41:15 am
[Lance Placey]"I have an ATI All-in-wonder card ( ATI RAGE PRO chipset ) and a Soundmax sound card."
Are you using the audio inputs on the ATI Capture card for the audio capture portion or are you using the soundcard inputs? If using the soundcard inputs you may have a sample rate issue or more than likely the sync clock for your video card on your ATI is out of sync with your audiocard's clock.
If using the audio inputs on the ATI card I would think audio would stay in sync with the video.
You could also check the sample rate of your captured avi clip by right clicking and choose properties. Take note of the sample rate and then set your Vegas Properties settings to match.
Regards, Rick.
Rick Mac
Director of Audio Production
TCT Network - Directv 377
Re: Sony Vegas 6 Capture - audio sync problem by Lance Placey on Feb 18, 2008 at 2:00:17 pm
After some further experimentation I came to the following conclusions...
The VHS that I am capturing from is pretty old and causes alot of screen flash/flicker. ( mostly toward the beginning of the tape.
What I did was break the tape up into segments and recorded each one. The later segments of the tape I had no problem with, and video and audio sync were fine. The first portion of the tape, where most of the screen flash and flicker occured was where my audio and video would get out of sync. After various attempts to record and re-record the first section of this tape I noticed that what I ended up with for video and what I saw as I previewed the capture process differed slightly. Following the capture I noticed that their seemed to be ever so slight jumping in certains sections of the capture as if frames were missing from the video capture.
It is my belief that the capture process is eliminating frames associated with the flash/flicker possibly as part of the compression process.. possibly as part of some sort of filtering process. The audio meantime has no issues and is fed back through my audio card for capture. Hence I end up with video and audio portions that are not the same in length. By clipping pieces of audio in strategic places and then stretching the audio clip to match the length of the video clip I manage to re-sync the A/V to something acceptable for this beginning portion.
The question remains as to what might cause this "clipping" of bad frames in the video. My suspicion is that it is actually associated with the video card or the ATI drivers, but I'm also supposing that there may be some setting in Vegas that allows this "filtering"
Re: Sony Vegas 6 Capture - audio sync problem by Rick Mac on Feb 20, 2008 at 3:38:49 am
In the broadcast world video tape machines have what is called a TBC ( Time Base Corrector ) on them. It's job is to handle those little tape glitches without dropping frames.
VHS can be pretty ruff. Sounds like you are loseing some of
your control track most likely tape edge damage is to blame.
If your tape does have damage you are already doing what I would suggest by manually slipping sync back in with editing.
By the way, some of the better analog to dv converters can clean up minor tape hits.
Regards, Rick.
Rick Mac
Director of Audio Production
TCT Network - Directv 377
