"I fields" are identical in all 3 clips but subsequent P or B fields are different in 1 vs (2 & 4). that is the reason you see "I- frame" has a different size. Your frame is consist of 2 fields actually where the bottom one is not "I".
Yes."I fields" should be the same and subsequent P or B fields are different in 1 vs (2 & 4).But the bottom field of "I-frame" is only related to "I field".Why does its size change?
The construction you name frame does not exist in that encoded sequences you provided. All of them field encoded. #1 is I fields only – so Top and Bottom fields are both Intra type. Other 2 bitstreams are very similar for first 2 fields - I and P fields – Top field is Intra, Bottom is P type
you are right. now I see your point - bottom P fields are really different in size. same size in GopRefDist 2 and 4 but different from GopRefDist = 1 case. can you upload a short sample of your original uncompressed clip? 16 field pair would be just right. also give us information on your CPU and driver version installed on the platform
The original stream contains 7 bitstream.The sample's PID is 0x4ec.I use MPEG-2 Demultiplexer,Intel MPEG-2 Decoder,Intel H264 Encoder and Intel MPEG2 Muxer to get the outcomes.
CPU: Intel(R) Core(TM) i5-4570 CPU @ 3.20GHz
OS: Microsoft Windows 7
Graphics Devices: Intel(R) HD Graphics 4600 10.18.14.4080
Dear Chi Xu, Thank you for your patience! so far issue was escalated but not yet confirmed. While you are waiting please take a chance to upgrade your graphics driver to latest. Currently available 4222 version, your 4080 is almost a half a year old.
Hi Chi Xu, sorry for a long turn around. I have got the confirmation that it is an expected behavior by design.
The main reason is the adaptive rounding offset control. When there is no B frame/field, the rounding offset for P frame is minimal to reduce the frame size. When there are B fields, the rounding offset for P field is bigger, so P field quality can be improved because it is used as reference for B field. The reference frame size increase to be compensated by overall PSNR improvement.