There is provided a method for clock reference insertion during packetization of an encoded data stream, wherein said packetization is performed before buffering of the data stream. The method comprises storing the value of each bit rate applied during encoding, and the duration of time for which each bit rate is applied. A clock reference time interval is converted into a clock reference data interval using the value of each bit rate applied and the duration of time for which each bit rate is applied. The clock reference data interval is used to determine where to insert a clock reference into the data stream during packetization.