1. A decoder, comprising: a pre-unit, for separating a data stream into various packets and providing each packet with a packet information, wherein each packet information corresponds to each packet and includes a packet identification; a database, for recording a plurality of setting parameter sets; at least one data filter, for comparing the data stream with a operation parameter set saved therein, and outputting a comparing result; and a scheduler, coupled to the pre-unit, the database, and the data filter, for fetching corresponding at least one setting parameter set from the database according to the packet identification of the packet information provided by the pre-unit and saving the setting parameter set fetched from the database into the data filter, which has a minimum probability to be used, as the operation parameter set, wherein the packet identification of each packet is first transmitted to the scheduler, and the setting parameter set corresponding to the packet identification is written into the data filter by the scheduler before each packet is transmitted to the data filter.