Extension decoder for decoding a sequence of packets, wherein the extension decoder comprises an extended functionality as compared to a basic decoder, comprising: a receiver for receiving the sequence of packets for which a packet syntax is specified, the sequence of packets comprising at least one data packet and at least one replacement packet, the replacement packet being a valid packet with regard to the packet syntax, audio content of the replacement packet being predetermined valid audio content reproducible by the basic decoder and having a predetermined content characteristic and the replacement packet containing an indication for the fact that the same is a replacement packet, wherein the indication is such that the basic decoder can receive the replacement packet and the replacement packet can be decoded like a valid packet according to the predetermined content characteristic; detector for detecting whether a packet of the sequence of packets contains the indication and consequently is the replacement packet, wherein the detector is implemented to interpret the indication; error concealing means for synthesizing synthesis audio content for the replacement packet by means of an error concealing measure, the synthesis audio content comprising a content characteristic differing from the predetermined content characteristic of the audio content of the replacement packet; and audio rendering means for rendering the audio content of a packet of the sequence of packets when the packet of the sequence of packets is the data packet and for rendering the synthesis audio content when the packet of the sequence of packets is the replacement packet. a receiver for receiving the sequence of packets for which a packet syntax is specified, the sequence of packets comprising at least one data packet and at least one replacement packet, the replacement packet being a valid packet with regard to the packet syntax, audio content of the replacement packet being predetermined valid audio content reproducible by the basic decoder and having a predetermined content characteristic and the replacement packet containing an indication for the fact that the same is a replacement packet, wherein the indication is such that the basic decoder can receive the replacement packet and the replacement packet can be decoded like a valid packet according to the predetermined content characteristic; the sequence of packets comprising at least one data packet and at least one replacement packet, the replacement packet being a valid packet with regard to the packet syntax, audio content of the replacement packet being predetermined valid audio content reproducible by the basic decoder and having a predetermined content characteristic and the replacement packet containing an indication for the fact that the same is a replacement packet, wherein the indication is such that the basic decoder can receive the replacement packet and the replacement packet can be decoded like a valid packet according to the predetermined content characteristic; detector for detecting whether a packet of the sequence of packets contains the indication and consequently is the replacement packet, wherein the detector is implemented to interpret the indication; error concealing means for synthesizing synthesis audio content for the replacement packet by means of an error concealing measure, the synthesis audio content comprising a content characteristic differing from the predetermined content characteristic of the audio content of the replacement packet; and audio rendering means for rendering the audio content of a packet of the sequence of packets when the packet of the sequence of packets is the data packet and for rendering the synthesis audio content when the packet of the sequence of packets is the replacement packet.