A method of processing video data, wherein the video data comprises a plurality of operation points, wherein each operation point is identified by a set of layer identifiers denoted by a variable OpLayerIdSet, and a temporal identifier for the operation point, denoted by a variable OpTid, the method comprising: performing a hypothetical reference decoder, HRD, operation, wherein the HRD operation determines conformance of a bitstream comprising encoded video data to a video coding standard or determines conformance of a video decoder to the video coding standard, wherein performing the HRD operation comprises: selecting, from the plurality of operation points, an operation point under test; setting a variable which indicates a target highest temporal identifier of a bitstream-subset associated with the selected operation point under test to be equal to OpTid for the operation point under test; determining, based on the target highest temporal identifier, a particular first syntax element from among a first array of syntax elements included in the bitstream, the first array of syntax elements specifying, for respective values of highest temporal identifier, a maximum required size of a decoded picture buffer, DPB; determining, based on the target highest temporal identifier, a particular second syntax element from among a second array of syntax elements included in the bitstream, the second array of syntax elements specifying, for respective values of highest temporal identifier, a maximum allowed number of pictures preceding any picture in decoding order and succeeding that picture in output order; determining, based on the highest temporal identifier, a particular third syntax element from among a third array of syntax elements included in the bitstream, wherein respective syntax elements in the third array of syntax elements specify, for each respective value of highest temporal identifier, a number minus 1, of alternative coded picture buffer, CPB, specifications in the bitstream; and using the particular first, second and third syntax elements in the HRD operation. selecting, from the plurality of operation points, an operation point under test; setting a variable which indicates a target highest temporal identifier of a bitstream-subset associated with the selected operation point under test to be equal to OpTid for the operation point under test; determining, based on the target highest temporal identifier, a particular first syntax element from among a first array of syntax elements included in the bitstream, the first array of syntax elements specifying, for respective values of highest temporal identifier, a maximum required size of a decoded picture buffer, DPB; determining, based on the target highest temporal identifier, a particular second syntax element from among a second array of syntax elements included in the bitstream, the second array of syntax elements specifying, for respective values of highest temporal identifier, a maximum allowed number of pictures preceding any picture in decoding order and succeeding that picture in output order; determining, based on the highest temporal identifier, a particular third syntax element from among a third array of syntax elements included in the bitstream, wherein respective syntax elements in the third array of syntax elements specify, for each respective value of highest temporal identifier, a number minus 1, of alternative coded picture buffer, CPB, specifications in the bitstream; and using the particular first, second and third syntax elements in the HRD operation.