CBR vs VBR

[Tero Ahlfors]

[Devinda Fernando] “So you don’t actually know the methodology of how Adobe Premiere reduces the file size when the Bitrate setting is reduced for the Export?”

It’s a combination of bitrate, macroblock compression and GOP, there are some settings you can tweak depending on, for example, some specific delivery specs.. The compression runs automatically so you can’t go and tweak it on frame by frame basis. If you really need to know how the math works then read the book or start with this https://en.wikipedia.org/wiki/H.262/MPEG-2_Part_2