[M4IF Technotes] Trouble with Bframe: size goes bigger

[Francesco Falconi]

Hello to everyone,
I hope someone can find two minutes to answer me. 
I show you this test: they are only 8 frames to compress, (frame base cosing). My test is about advantage in size compression using more bframe than Pframe. 
The GOP is 8 frame and i try to change the number of P-B frame (fixing numer of Iframe).
So i change the value of  Motion.PBetweenICount  and Motion.BBetweenPCount 
These are the results:
      P=    B=
     GOP 
     Size cmp
     fps
      0    6
     I B B B B B B I
     15944
     0,4097
      1    3
     I B B B P B B I
     14804
     1,3095
      3    1
     I B P B P B P I
     14065
     2,4133
      6    0
     I P P P P P P I
     14023
     2,8229
I cant't understand why adding Bframe the size goes bigger, it could be the opposite (accordin Mpeg Theory). I try to make other test, the same results.
Could you explain me the reason?
Thank you vaery much, this is for my university thesis.
Francesco Falconi
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