The contribution proposes a syntax element (nuh_pic_id) in the NAL unit header, which has the same value with the LSB values of the picture order count. The proposed syntax element (nuh_pic_id) is an identifier for each picture and can be used for the access unit identification at the system level. A network element or a video player can easily access VCL NAL units belonging to the same access unit. It is asserted that, especially when multiple video components are coded with multiple layers (or with multiple coded vide sequences) and simultaneously contained in the same coded bitstream, exposing the value of the picture order count in NAL unit header layer is very helpful for a media player or a file writer to access pictures belonging the same access unit or the same time instance, and synchronize multiple NAL units corresponding to different components for extracting, editing, writing or playing back.