An apparatus configured to decode video data, the apparatus comprising: a memory configured to store the video data; and a video decoder in communication with the memory, the video decoder configured to: receive a first decoded picture buffer DPB output delay and a second DPB output delay in a picture timing SEI message; receive a sub-picture coded picture buffer, CPB flag; determine whether a hypothetical reference decoder, HRD, setting for a video decoder indicates operation at a picture level or operation at a sub-picture level based on the sub-picture CPB flag; and based on a determination that the HRD setting indicates operation at the picture level, determine, for the decoded picture, a first DPB output time by multiplying the first DPB output delay by a picture clock tick and adding a resultant value to a CPB removal time, and outputting pictures from a decoded picture buffer based on the first DPB output time; and based on a determination that the HRD setting indicates operation at the sub-picture level, deriving a sub-picture clock tick based on the picture clock tick and a tick divisor value whereby the sub-picture clock tick equals the picture clock tick divided by the tick divisor value; determine, for the decoded picture, a second DPB output time by multiplying the second DPB output delay by a sub-picture clock tick and adding a resultant value to a CPB removal time and outputting pictures from a decoded picture buffer based on the second DPB output time. a memory configured to store the video data; and a video decoder in communication with the memory, the video decoder configured to: receive a first decoded picture buffer DPB output delay and a second DPB output delay in a picture timing SEI message; receive a sub-picture coded picture buffer, CPB flag; determine whether a hypothetical reference decoder, HRD, setting for a video decoder indicates operation at a picture level or operation at a sub-picture level based on the sub-picture CPB flag; and based on a determination that the HRD setting indicates operation at the picture level, determine, for the decoded picture, a first DPB output time by multiplying the first DPB output delay by a picture clock tick and adding a resultant value to a CPB removal time, and outputting pictures from a decoded picture buffer based on the first DPB output time; and based on a determination that the HRD setting indicates operation at the sub-picture level, deriving a sub-picture clock tick based on the picture clock tick and a tick divisor value whereby the sub-picture clock tick equals the picture clock tick divided by the tick divisor value; determine, for the decoded picture, a second DPB output time by multiplying the second DPB output delay by a sub-picture clock tick and adding a resultant value to a CPB removal time and outputting pictures from a decoded picture buffer based on the second DPB output time. receive a first decoded picture buffer DPB output delay and a second DPB output delay in a picture timing SEI message; receive a sub-picture coded picture buffer, CPB flag; determine whether a hypothetical reference decoder, HRD, setting for a video decoder indicates operation at a picture level or operation at a sub-picture level based on the sub-picture CPB flag; and based on a determination that the HRD setting indicates operation at the picture level, determine, for the decoded picture, a first DPB output time by multiplying the first DPB output delay by a picture clock tick and adding a resultant value to a CPB removal time, and outputting pictures from a decoded picture buffer based on the first DPB output time; and based on a determination that the HRD setting indicates operation at the sub-picture level, deriving a sub-picture clock tick based on the picture clock tick and a tick divisor value whereby the sub-picture clock tick equals the picture clock tick divided by the tick divisor value; determine, for the decoded picture, a second DPB output time by multiplying the second DPB output delay by a sub-picture clock tick and adding a resultant value to a CPB removal time and outputting pictures from a decoded picture buffer based on the second DPB output time.