B-Frames In second pass

[ShaoMonk]

Hi..

when i used b-frames 2 or 1 in first pass.. can i change this.. in second pass.. without doing the first pass again?

bye

also want to know whats wrong about undersized files.. i cant get 2 cd size.. with this settings:

quantization type: mpeg
vhq mode: 1
max i frame:250
min i frame:1
b-frame: 2
b-frame ratio:150
b-frame offset:75

xvid build: 16.07.2003

[Koepi]

ShaoMonk,

use the search function, this question has been answered at least 3 times.

You need to redo your first pass as the bframes settings affect compressability.

Regards
Koepi

[Didée]

@ Koepi

A quick follow-up:

What if I change B-frames ratio & offset in a way that still give the same quants for B-frames in the 1st pass?
E.g. on 1st pass, B-frame settings were 2/200/0.
On 2nd pass, B-frame settings were 2/150/100.

This both settings give exactly the same output in the 1st-pass, but (would) behave quite different in the 2nd-pass.

Does this make a difference, or not? Or, in other words, are the B-frame settings of the 1st-pass actually remembered somehow, or does the scaling routines only rely on size & quant of 1st-passes B-frames?

For those who don't live'n sleep in the XviD sources ;)

- Didée

[YY1020]

I think that you are setting two-pass as same as one-pass may as well do.

[mf]

Originally posted by Didée
@ Koepi

A quick follow-up:

What if I change B-frames ratio & offset in a way that still give the same quants for B-frames in the 1st pass?
E.g. on 1st pass, B-frame settings were 2/200/0.
On 2nd pass, B-frame settings were 2/150/100.

This both settings give exactly the same output in the 1st-pass, but (would) behave quite different in the 2nd-pass.

Does this make a difference, or not? Or, in other words, are the B-frame settings of the 1st-pass actually remembered somehow, or does the scaling routines only rely on size & quant of 1st-passes B-frames?

For those who don't live'n sleep in the XviD sources ;)

- Didée
What you'll find by setting Discard First Pass off is that B-frames are already scaled in first pass.

[Didée]

Of course they are already scaled.
I was aiming for that: does it make a difference by what B-frame settings the given B-frame-quant in 1st pass was reached, when calculating the quantizers for the 2nd pass.
And - obviously, it makes no difference. At least, it shouldn't. After 1st-pass, the B-frames *have* a specific size at a *certain* quantizer, and that's all that's needed to estimate bitrate distribution in the 2nd pass.

Sometimes you simply have to speak out some nonsense loud, in order to reckognize that it's *nonsense*. Sorry.

- Didée