B-frames: 1st, 2nd, or both passes?

[spstrikwerda]

hi there,


a while ago i started using B-frames in XviD, but i have a little dilemma:

- should i use B-frames only in the 1st pass, or only the 2nd, or both passes?
- when i enable them in both passes, my filesize comes out right, but when i only use B-frames in 2nd pass, the filesize gets about 150 mb under the desired size.

i experimented with DebugView, and came to the conclusion that only using B-frames in 2nd pass, results in much higher quant. (used a test clip of 1 minute length, Q2: 1400, Q3: 85, Q4: 15).

anybody advice on this? tnx!

[Sigmatador]

should i use B-frames only in the 1st pass, or only the 2nd, or both passes?
THE BOTH!!!

when i enable them in both passes, my filesize comes out right, but when i only use B-frames in 2nd pass, the filesize gets about 150 mb under the desired size.
all is normal :D (the 1st pass stats file don't have the compressibility gain offered by the bframe)

i experimented with DebugView, and came to the conclusion that only using B-frames in 2nd pass, results in much higher quant. (used a test clip of 1 minute length, Q2: 1400, Q3: 85, Q4: 15).
normal too. b-frames = equivalent quality with higher quant (so better compressibility)

[spstrikwerda]

tnx! i'll encode a few more clips to find the best settings :D

by the way, can i set video in VirtualDub to "fast recompress", or do i have to use "full processing mode" ??? (regarding luma masking etc.)

[Sigmatador]

fast recompress to avoid pointless conversion ( virtualdubmod with avisynth 2.5 to work in the YV12 colorspace)

[ssjkakaroto]

Sigmatador wasnt there a bug using b-frames on both passes and the fix for it wasnt just use them on the second pass?

[Sigmatador]

with the last koepi's build (17022003) i can't see any darkblock or artefact on bframes. (bframe activated for the both pass --> options which modify the 1st pass size must be activated in the both pass)
i've just notice that qpel is better with h263 than mpeg and darkscene are better with no qpel and mpeg (it's my point a view :D, need a dynamic hpel/qpel :cool: )

[ssjkakaroto]

that's great to hear! :D