Syntax structures that indicate the completion of coded regions of pictures are described. For example, a syntax structure in an elementary bitstream indicates the completion of a coded region of a picture. The syntax structure can be a type of network abstraction layer unit, a type of supplemental enhancement information message or another syntax structure. For example, a media processing tool such as an encoder can detect completion of a coded region of a picture, then output, in a predefined order in an elementary bitstream, syntax structure(s) that contain the coded region as well as a different syntax structure that indicates the completion of the coded region. Another media processing tool such as a decoder can receive, in a predefined order in an elementary bitstream, syntax structure(s) that contain a coded region of a picture as well as a different syntax structure that indicates the completion of the coded region.