A method for decoding video data in accordance with High Efficiency Video Coding, HEVC, the video data comprising an access unit, AU, the access unit comprising a plurality of decoding units, DUs, the plurality of DUs of the AU including one DU that is last in the AU in decoding order and a plurality of DUs that are not last in the AU in decoding order, the method comprising, when a first flag has a value that indicates that sub-picture coded picture buffer, CPB, parameters are present in the video data: decoding, for each DU of the AU other than the DU of the AU that is last in decoding order, a duration value, in terms of a number of sub-picture clock ticks, between a nominal CPB removal time (140-1, 142-1) of the DU (110-1, 112-1) and a nominal CPB removal time (140-2, 142-2) of an immediately subsequent DU (110-2, 112-2) in decoding order, the duration values for the DUs being decoded from a picture timing supplemental enhancement information, SEI, message associated with the AU when a second flag has a value that indicates that sub-picture CPB parameters are present in picture timing SEI messages and decoded from a sub-picture timing SEI message associated with the AU when the second flag has a value that indicates that sub-picture CPB parameters are not present in picture timing SEI messages, wherein the second flag is a sequence-level flag; determining, for each DU of the AU, a CPB removal time for the DU; and for each DU of the AU, at the determined CPB removal time for the DU, decoding video data associated with the DU and removing the DU from the CPB, wherein the decoding of the video data is performed with low_delay_hrd_flag equal to 0, wherein the CPB removal time for the DU that is last in the AU in decoding order is set equal to a nominal CPB removal time for the AU and the CPB removal time for the remaining DUs of the AU are set equal to respective nominal CPB removal times for the DUs, wherein, when the second flag has a value that indicates that sub-picture CPB parameters are present in picture timing SEI messages, the nominal CPB removal time for each DU in the AU other than the last DU in decoding order is determined by computing the nominal CPB removal time of the immediately subsequent DU in decoding order minus a length of time equal to the decoded duration value multiplied by the duration of a sub-picture clock tick, wherein, when the second flag has a value that indicates that sub-picture CPB parameters are not present in picture timing SEI messages, the nominal removal time for each DU in the AU other than the last DU in decoding order is determined by computing the nominal removal CPB removal time for the AU minus a length of time equal to the decoded duration value multiplied by the duration of a sub-picture clock tick. decoding, for each DU of the AU other than the DU of the AU that is last in decoding order, a duration value, in terms of a number of sub-picture clock ticks, between a nominal CPB removal time (140-1, 142-1) of the DU (110-1, 112-1) and a nominal CPB removal time (140-2, 142-2) of an immediately subsequent DU (110-2, 112-2) in decoding order, the duration values for the DUs being decoded from a picture timing supplemental enhancement information, SEI, message associated with the AU when a second flag has a value that indicates that sub-picture CPB parameters are present in picture timing SEI messages and decoded from a sub-picture timing SEI message associated with the AU when the second flag has a value that indicates that sub-picture CPB parameters are not present in picture timing SEI messages, wherein the second flag is a sequence-level flag; determining, for each DU of the AU, a CPB removal time for the DU; and for each DU of the AU, at the determined CPB removal time for the DU, decoding video data associated with the DU and removing the DU from the CPB, wherein the decoding of the video data is performed with low_delay_hrd_flag equal to 0, wherein the CPB removal time for the DU that is last in the AU in decoding order is set equal to a nominal CPB removal time for the AU and the CPB removal time for the remaining DUs of the AU are set equal to respective nominal CPB removal times for the DUs, wherein, when the second flag has a value that indicates that sub-picture CPB parameters are present in picture timing SEI messages, the nominal CPB removal time for each DU in the AU other than the last DU in decoding order is determined by computing the nominal CPB removal time of the immediately subsequent DU in decoding order minus a length of time equal to the decoded duration value multiplied by the duration of a sub-picture clock tick, wherein, when the second flag has a value that indicates that sub-picture CPB parameters are not present in picture timing SEI messages, the nominal removal time for each DU in the AU other than the last DU in decoding order is determined by computing the nominal removal CPB removal time for the AU minus a length of time equal to the decoded duration value multiplied by the duration of a sub-picture clock tick.