2 frame shift between original video & avs script

[nautilus7]

I am trying to re-encode a PAL DVD (mpeg-2). I use DGIndex to create a .d2v file to make an .avs script (a simple one).

When i load the 1st .vob file of the dvd and the .avs into 2 different VirtualDubMod instances, i notice a 2 frame shift (what is on frame x in the .vobs is on x+2 in the .avs).

Why is that? Does it has to do with the frame type order (I, P, B)? Frame order in the .d2v file is like this: [B][B][I][B][B][P]

How does it affect the calculated delay by DGIndex (-8ms in this case)?

EDIT: I forgot to mention that total number of frames in .d2v and .avs is the same.

[Guest]

VirtualDubMod discards the nondecodable leading B frames while DGIndex replaces them with copies of the first decodable frame (to keep the original frame count). DGIndex calculates the delay based on the retention of these frames.

[nautilus7]

So, everything is fine and no reason to worry. Thanks, neuron2!