VirtualDubMod always shows 2 B frames before an I frame

[stevem99]

I am trying to combine some short VOB clips into one clip. I use DVD2AVI to find the clip points LBA by saving as a project and then using the Location it gives me in the project file to find the LBA split points.

The start number is SUPPOSED to be an I frame. I then use Vstrip and put in the start LBA number and it gives me the clip. However, when joining the clips there is usually some black blocks at the first part of each of the joined clips. So I put the individual VOB clip into VirtualDubMod and there is almost always 2 B frames at the start before the I frame.

So could someone tell me what is going on here and how to get the clip to start with an actual I frame?? I am posting this in both VirtualDubMod and DVD2AVI forums.

[neuron2]

VDubMod is just following the MPEG2 spec:

6.1.1.11 Frame re-ordering

[...]

When B-frames are present in the sequence, re-ordering is performed according to the following rules:

- If the current frame in coded order is a B-frame, the output frame is the frame reconstructed from that B frame.

- If the current frame is a I-frame or P-frame, the output frame is the frame reconstructed from the previous I-frame or P-frame, if one exists. If none exists, at the start of the sequence, no frame is output.

That means it is quite legal for a sequence to start by displaying B frames.

BTW, don't you know that forum rules prohibit cross-posting?

[fccHandler]

If you're talking about the most recent VirtualDubMod, then it's the code they've borrowed from me which is showing you black blocks. There's an old discussion about that code (and the blocks) here (http://forum.doom9.org/showthread.php?s=&threadid=46606).

P.S. I have yet to see a DVD VOB with all closed GOPs, so if you strip it from any GOP except the first, you're likely to get black blocks in the first couple of frames.