1. A video stream decoding method comprising: obtaining random access point (RAP) reference layer number information indicating the number of layers referred to for performing inter layer prediction on RAP images among current layer images and non-RAP reference layer number information indicating the number of different layers referred to for performing inter layer prediction on non-RAP images, from a video stream regarding images encoded for a plurality of layers; obtaining RAP reference layer identification information for each layer referred to for predicting the RAP images based on the obtained RAP reference layer number information, from the video stream; obtaining non-RAP reference layer identification information for each layer referred to for predicting the non-RAP images based on the obtained non-RAP reference layer number information, from the video stream; reconstructing an RAP image of a current layer based on a layer image indicated by the obtained RAP reference layer identification information; and reconstructing a non-RAP image of the current layer based on a layer image indicated by the obtained non-RAP reference layer identification information.