mpg file size smaller than expected, TMPGEnc 2.5 VBR 2-pass mode

[chipsndukes]

I encoded an .mpg file with TMPGEnc 2.5 using 2-pass VBR.

I set the avg. bitrate to be 5991, but the final result checked in GSpot was 4350. I noticed because the file was much smaller than expected.

What could have caused this?

Source: .wmv file 23.976 fps
frame served via AviSynth
used 3:2 pulldown and unchecked the "enable padding not to be lower than minimum bitrate" box

It's not really important, the final product is fine, but I would like to know if someone could explain why this happened.

Thanks,
Chipsndukes

[chipsndukes]

I played around with the "enable padding not to be lower than minimum bitrate" setting and the minimum bitrate on a different clip, and got the final bitrate in GSpot to change a bit.

So, I guess my assumption now is that 2-pass VBR will not use more bitrate than necessary unless a) forced to by a minimum bitrate or b) padding.

Does that sound right?

Chipsndukes