Quantcast Panasonic S-VHS running slow? - digitalFAQ Forum
02-22-2020, 08:04 PM
bakerie bakerie is offline
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I was having issues with VirtualDub captures looking "juddery". I fixed this by disabling the option to add frames when there is some missing. The reason Vdub is inserting so many though appears to be (according to Vdub) the VCR is only outputting 24.5 FPS instead of 25.

Is it possible to adjust this internally on the VCR? This is a tape that was recorded and played back on the same machine.
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02-22-2020, 09:18 PM
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You must have an external framesync TBC between the VCR and capture card/device. That should resolve this problem.

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02-23-2020, 05:31 AM
bakerie bakerie is offline
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Hmmm. Yes an external TBC would correct the issue, but that's surely the wrong way to go about fixing this issue?

If I had a prerecorded tape that was outputting 24.5fps than TBC would be the answer as the tape is already made, but if I'm recording and playing back footage that's being mastered at the wrong frame rate, surely you fix the problem at the source, not try and correct it with band aids later?
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02-23-2020, 06:29 AM
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Actually, on further investigation, this isn't related to the VHS player at all. I'm using a DVD player to test and I'm still getting 24.6 FPS. Is this a capture card issue? Timing on the PC is screwed?
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02-23-2020, 07:15 AM
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EDIT: Can an admin change the thread title to something more relevant in case someone has the same problem in the future?

Well that was an adventure, but I got there!

Documenting this for anyone with the same issue.

Two tools to fix this:
Windows timer tester to check system clock accuracy: https://www.ghacks.net/download/99427/
Timertool V3 to increase clock precision: https://vvvv.org/contribution/windows-system-timer-tool

First you can use Windows Timer Tester to check the current timer accuracy. I was able to see that the framerate Vdub was reporting was being manipulated linearly with the system timer accuracy. For some reason (possible battery saving for laptops?) the precision was set to 15ms, need to get this lower. First use Timertool V3 to set the precision to 1ms.

Now you can check your accuracy again with Timer tester and you should see it has increased. Mine was up to 24.89 FPS from 24.6 with this fix, but this obviously isn't good enough.

Probably our HPET timer is shite, or we aren't using it at all. We can check and see which is true by entering the below commands in an admin elevated command prompt:

To enable HPET as the only timer run the command "bcdedit /set useplatformclock true"
To disable HPET in Windows run the command "bcdedit /deletevalue useplatformclock"

For me, I had to disable the platform clock. Vdub is now showing a relatively smooth 24.99fps
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The following users thank bakerie for this useful post: msgohan (02-24-2020)
02-24-2020, 08:05 PM
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Intriguing info. Thanks.
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