The disclosure relates to a device for transmitting a data stream and a device for receiving a data stream. Disclosed is a device for transmitting a data stream including: an encoder configured to generate a compressed bitstream by encoding input media, generate additional information about the compressed bitstream, and generate a data stream (DS) including the additional information and the compressed bitstream, wherein the additional information includes at least one class information indicating an importance of the compressed bitstream, and a DS transmitter configured to generate a packet by packing the data stream, transmit a plurality of packets including the generated packet to a reception device, and retransmit at least some of the plurality of packets due to transmission error, wherein the retransmitted packets are identified based on at least corresponding class information.