A method comprising: associating a first set of data units into a first bitstream partition and associating a second set of data units into a second bitstream partition, where the first set comprises data units different from those of the second set; inputting the first bitstream partition into a first buffer; inputting the second bitstream partition into a second buffer; obtaining buffering parameters for at least one of the second bitstream partition and the second buffer; and using the buffering parameters in at least one of inputting the second bitstream partition into the second buffer and outputting from the second buffer.