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View Full Version : General question about audio sync and waveform scopes


FlimsyFeet
24th March 2005, 12:42
(I wasn't really sure where to post this, as it transcends several different forum topics.)

I've been capturing some VHS tapes with VirtualVCR (using the "dynamic resample audio" option). Mostly the audio sync is fine, but in one or two parts where there are dropouts on the tape and the capture has dropped frames, the sync goes a little bit off for a few minutes.

Is there such a thing as a filter for VirtualDub or AviSynth that will give you a frame from an AVI file with an waveform scope below it representing the slice of the audio associated with that particualr frame? You know, like in TMPGEnc when you select "source range", there's a display of the audio below?

The next question is, say there's a clearly identifiable sound such as a gunshot or impact that you want to use to help getting things back into sync, where should the start of that sound be in the frame? At the start, or in the middle, or near the end, or does is not really matter as long as it's in the correct frame? I've read somewhere that errors of +20 ms (audio advanced) and -40 ms (audio delayed) were detectable. When dealing with PAL film material each frame is 40ms.

Wilbert
24th March 2005, 13:06
Is there such a thing as a filter for VirtualDub or AviSynth that will give you a frame from an AVI file with an waveform scope below it representing the slice of the audio associated with that particualr frame?
AudioGraph.


The next question is, say there's a clearly identifiable sound such as a gunshot or impact that you want to use to help getting things back into sync, where should the start of that sound be in the frame? At the start, or in the middle, or near the end, or does is not really matter as long as it's in the correct frame?
In the middle? I don't think there is a good answer to this. I mean, can you really see that this gunshot happens exactly on a frame or does it happen between two frames, etc.

ppera2
24th March 2005, 18:15
Idea is maybe not bad, I mean to get some help by determining value of A/V desync. But...
This will not fix your capturing. And if async varies, fixing is very hard.
I can only suggest that try Virtual Dub 1.64 instead Virtual VCR. Many people here had very good experiences with...