Method and apparatus of scaling window constraint for worst case bandwidth consideration for reference picture resampling in video coding

An apparatus for coding a video sequence, wherein a Reference Picture Resampling (RPR) mode is supported, the apparatus comprising one or more electronic circuits or processors arranged to:

• generate, at an encoder side, or receive, at a decoder side, a bitstream corresponding to encoded data of the video sequence, wherein the bitstream comprises one or more syntaxes related to the RPR mode when the RPR mode is enabled, and scaling information for the RPR mode is derived using said one or more syntaxes, and wherein said one or more syntaxes are constrained by taking into account a value corresponding to Max(8, (minimum coding block size for a luma component));
• wherein the minimum coding block size for the luma component is indicated by one variable, MinCbSizeY, wherein said one or more syntaxes comprise a first syntax corresponding to current picture width in luma samples and a second syntax corresponding to maximum picture width in the luma samples, wherein said one or more syntaxes are constrained to cause ((the current picture width−Max(8, MinCbSizeY))*scaling window width of reference picture in the luma samples) to be smaller than or equal to (the maximum picture width*scaling window width of a current picture), and wherein a target picture of the video sequence is encoded, at the encoder side, or decoded at the decoder side, utilizing the scaling information.