VirtualDub - constant frame rate vs. variable FPS?

[Zerowalker]

I know that when you capture, you are pretty much never going to get a constant FPS, the clock sync between devices are never precise and you will never get that 30fps you are supposed to.

However, i am wondering, is it possible to capture Variable FPS with Virtualdub?

I know it should be possible to capture, i can do it in Graphstudio, but in Virtualdub it want´s to always set a FPS and then play it to that later.

[lordsmurf]

I'm not aware of any such error -- and I do mean "error", not "feature". Because that's what it would be. No TV (or even a streaming player) could ever play back such a problematic video. It expects (and therefore requires) consistency in the video stream. The signal locks to this, and is how the stream self-audits itself. For example, the ability to drop frames, or the ability to sync audio.

True, no capture is ever 100% perfect to the framerate, but that's because of the chaotic nature of analog video. However, it is close. For example, a brief few frames may be 29.971 or 29.969 in stead of 29.970.

Once digitized, it is a perfect 29.97001 frame rate (or whatever it is).

Like pi (3.14159...), I think the actual math for NTSC video is imperfect with an enormous decimal place.

[Zerowalker]

True, but mine isn´t so close that it isn´t noticeable.
To get it as good as possible, i have to save it at any framerate, disable all resync, drop frames etc.

Then use the Time Log that Virtualdub can give you at the end, and sync manually.
That way i will get the best result with no dropped/inserted frames or desync.

But for my problem, it isn´t actually in Analogue i am having trouble, but it´s my Webcam.

If i choose 30fps, it will be at an average rate of 29.874, which is very far away, so the only way i can get the correct speed is to tell it afterwards and change it, or save it in a Variable Framerate, meaning it will save in the framerate that it has in the end, to have the correct speed throughout the video.

[kpmedia]

If it were me, I'd just get a different webcam.

[Zerowalker]

The problem is, how do i know that others aren´t the same.
Also, 25fps seems to be at about 25fps, so it´s 30fps that "fails".

[NJRoadfan]

Quote:

Originally Posted by lordsmurf

Once digitized, it is a perfect 29.97001 frame rate (or whatever it is).

Like pi (3.14159...), I think the actual math for NTSC video is imperfect with an enormous decimal place.

Its technically 30/1.001.

As for the webcam, buggy drivers can drop frames silently without VirtualDub even knowing about it.

[Zerowalker]

Well buggy drivers is it´s own story, didn´t know it could drop frames without VirtualDub knowing though.
I think however, mine doesn´t, as i got a TimeStamp running on it as a PostProcess, and it´s correct, which it probably wouldn´t be if it dropped frames (if i drop/insert with VirtualDub it is out of sync).

Guess i will have to ask someone with a Webcam to do a VD test for me or something.