Processing methods and apparatuses for video data comprise receiving input data associated with a current coding block (CB) in a current slice, deriving a top-left location of a current quantization group containing the current CB using a recursive process or a tracking process, and determining a reference quantization parameter (QP) according to the top-left location of the current quantization group. The current CB is encoded or decoded according to the reference QP. The reference QP may be further derived based on a previous QP determined by a tracking method.