Provided is a method for calculating a timestamp associated with a data packet before transcoding of the data packet. The method may include sampling a time of day (TOD) signal to provide a sampled TOD. A previously sampled TOD estimate may be retrieved. An internal TOD estimate may be determined based on the sampled TOD and the previously sampled TOD estimate. A timestamp may be determined based on the internal TOD estimate. A system and computer program product are also disclosed.