not an expert, but from what i understand is more like that they "extend" the codec with technique more effective on higher resolution content, or new "profile"

not an expert, but from what i understand is more like that they "extend" the codec with technique more effective on higher resolution content, or new "profile" (parameter) more effective for higher resolution content (a bit like you can have different parameter when you zip file). This new techniques can also be used for 1080p video (for example) but with lower gain. Also the "old" algorithm/system are generally still used but they may be improved/extend.