Why do different captures result in different timings?

[OBNOXIUs]

I'm capturing PAL VHS tapes using this workflow:

• JVC HR-S7600 => TBC-3000 => ATI 600 USB (Win10, VirtualDub2 to lossless FFV1)

Audio is captured with a separate Roland audio interface, which I understand is something other users here do also.
After capturing some tapes multiple times using the same equipment, I noticed that all my captures have different timings! Meaning that when I play them back at the same time, they drift apart. The A/V is in sync for each capture individually. Since I'm using a frame TBC, ánd VirtualDub reports no dropped or inserted frames, I'm a bit surprised...

I followed sanlyn's VirtualDub settings guide (including LS's remark about dropped/inserted frames tickbox).

If VirtualDub says no frames were dropped or inserted, where does this timing difference come from? All the frames are there, there is a constant framerate, audio is resampled to match the video... Does anybody here have experience with this? Thanks!

Karel

[lollo2]

Not sure I understand. If you write an avs file to watch 2 captures at the same time with VirtualDub, for example:

v1=AviSource(<file1>).trim(X,0)
v2=AviSource(<file1>).trim(Y,0)
stackhorizontal(v1, v2)

# where X and Y are appropriate to synch the 2 videos at the beginng

do you mean that moving inside Vdub at some point in time the 2 captures are not coincident anymore?

If that's the case, it is possible that the card (or the TBC) is dropping/inserting frames without "telling" it to the capture software. The dropped/insert frames reports are not always accurate.

Some reference here: https://forum.doom9.org/showthread.php?t=163958
If you search for jmac698 user on this topic you'll find many more...

[OBNOXIUs]

Thanks for the quick follow up. I hadn't come to trying Avisynth yet, but after installing it (and changing AviSource to DirectShowSource for FFV1) the conclusion is that the different captures are not drifting apart!

I've done so much A-B comparing with MPC-HC (for example of different encodes of the same source), and never had any speed or sync issues. It didn't occur to me that the problem could be in the playback software...

Thanks for the AviSynth way of A-B comparing.
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