A method of processing video data, the method comprising: determining a value of a first syntax element of a temporal motion constrained tile sets, MCTS, supplemental enhancement information, SEI, message of an access unit, wherein the value of the first syntax element represents whether or not each tile of one or more corresponding pictures is included in a separate MCTS; and when the value of the first syntax element does not indicate that each tile of the one or more corresponding pictures is included in a separate MCTS: i) determining , based on a value of a second syntax element of the temporal MCTS SEI message, a number of MCTS sets in the temporal MCTS SEI message, wherein the temporal MCTS SEI message includes a loop over the number of MCTS sets in the temporal MCTS SEI message, the loop including one iteration per set signaling values for one or more additional syntax elements for each MCTS set; and ii) based on the loop over the number of MCTS sets in the temporal MCTS SEI message, processing values of the one or more additional syntax elements for each MCTS set in the temporal MCTS SEI message and setting an MCTS identifier value of an MCTS of a current picture of the access unit equal to a value of an index of the MCTS set within the loop, the current picture being one of the one or more corresponding pictures, wherein the value of the index of the MCTS set within the loop is the value of a variable i, which is a loop counter that increments at each iteration of the loop. determining a value of a first syntax element of a temporal motion constrained tile sets, MCTS, supplemental enhancement information, SEI, message of an access unit, wherein the value of the first syntax element represents whether or not each tile of one or more corresponding pictures is included in a separate MCTS; and when the value of the first syntax element does not indicate that each tile of the one or more corresponding pictures is included in a separate MCTS: i) determining , based on a value of a second syntax element of the temporal MCTS SEI message, a number of MCTS sets in the temporal MCTS SEI message, wherein the temporal MCTS SEI message includes a loop over the number of MCTS sets in the temporal MCTS SEI message, the loop including one iteration per set signaling values for one or more additional syntax elements for each MCTS set; and ii) based on the loop over the number of MCTS sets in the temporal MCTS SEI message, processing values of the one or more additional syntax elements for each MCTS set in the temporal MCTS SEI message and setting an MCTS identifier value of an MCTS of a current picture of the access unit equal to a value of an index of the MCTS set within the loop, the current picture being one of the one or more corresponding pictures, wherein the value of the index of the MCTS set within the loop is the value of a variable i, which is a loop counter that increments at each iteration of the loop. i) determining , based on a value of a second syntax element of the temporal MCTS SEI message, a number of MCTS sets in the temporal MCTS SEI message, wherein the temporal MCTS SEI message includes a loop over the number of MCTS sets in the temporal MCTS SEI message, the loop including one iteration per set signaling values for one or more additional syntax elements for each MCTS set; and ii) based on the loop over the number of MCTS sets in the temporal MCTS SEI message, processing values of the one or more additional syntax elements for each MCTS set in the temporal MCTS SEI message and setting an MCTS identifier value of an MCTS of a current picture of the access unit equal to a value of an index of the MCTS set within the loop, the current picture being one of the one or more corresponding pictures, wherein the value of the index of the MCTS set within the loop is the value of a variable i, which is a loop counter that increments at each iteration of the loop. <EOS>