[Mp4-tech] [H.264] Using B-Frames & Reducing Bitrate Problem

[Ertuğrul Doğan (Design Engineer - VESTEK)]

Hi all,
I was experimenting with JM 11.0 software. I encoded the famous Foreman sequence with Qp = 28, GOP = IBPBP... with Intra period of 10. The Qp was the same for I, B and P frames. Also NumberReferenceFrames =  1.
I used the same configuration for IPPP... for the same sequence. In the end IPPPP.... GOP configuration resulted in a better bitrate. 
Isn't this weird ? Doesn't B frames supposed to reduce the bitrate with the same PSNR value ?
Thanks,
e.dogan
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