Video processing method for remapping sample locations in projection-based frame with projection layout to locations on sphere and associated video processing apparatus

A video processing method includes: decoding apart of a bitstream to generate a decoded frame, where the decoded frame is a projection-based frame that includes projection faces in a projection layout; and remapping sample locations of the projection-based frame to locations on the sphere, where a sample location within the projection-based frame is converted into a local sample location within a projection face packed in the projection-based frame; in response to adjustment criteria being met, an adjusted local sample location within the projection face is generated by applying adjustment to at least one coordinate value of the local sample location within the projection face, and the adjusted local sample location within the projection face is remapped to a location on the sphere; and in response to the adjustment criteria not being met, the local sample location within the projection face is remapped to a location on the sphere.