A portable device comprising: a storage unit (620, 1204) configured to store a plurality of multimedia files encoded in a predetermined format; a decoder unit configured to decode digital data included in the plurality of multimedia files; a USB device controller (820, 3261) configured to transmit the decoded digital data to an external device having a USB host controller (810, 3205); and a control unit (610, 1205) configured to: receive, via the USB device controller, from the external device, a control signal corresponding to a user input of selecting a multimedia file from among a list of the plurality of multimedia files, the list of the plurality of multimedia files being displayed on the external device, the user input being received by the external device; cause the decoder unit to decode digital data of the multimedia file, and transmit, via the USB device controller, to the external device, the decoded digital data of the multimedia file and reproduction state information, such that the decoded digital data of the multimedia file is reproduced via the external device, and that the reproduction state information is displayed via the external device in relation to reproduction of the multimedia file, wherein the control unit is further configured to receive, via the USB device controller, from the external device, a control signal corresponding to a user input of pausing, and in response to receiving the control signal corresponding to the user input of pausing, cause the decoder unit to pause decoding the multimedia file, and transmit, via the USB device controller, the reproduction state information indicating pausing to the external device. a storage unit (620, 1204) configured to store a plurality of multimedia files encoded in a predetermined format; a decoder unit configured to decode digital data included in the plurality of multimedia files; a USB device controller (820, 3261) configured to transmit the decoded digital data to an external device having a USB host controller (810, 3205); and a control unit (610, 1205) configured to: receive, via the USB device controller, from the external device, a control signal corresponding to a user input of selecting a multimedia file from among a list of the plurality of multimedia files, the list of the plurality of multimedia files being displayed on the external device, the user input being received by the external device; cause the decoder unit to decode digital data of the multimedia file, and transmit, via the USB device controller, to the external device, the decoded digital data of the multimedia file and reproduction state information, such that the decoded digital data of the multimedia file is reproduced via the external device, and that the reproduction state information is displayed via the external device in relation to reproduction of the multimedia file, wherein the control unit is further configured to receive, via the USB device controller, from the external device, a control signal corresponding to a user input of pausing, and in response to receiving the control signal corresponding to the user input of pausing, cause the decoder unit to pause decoding the multimedia file, and transmit, via the USB device controller, the reproduction state information indicating pausing to the external device. receive, via the USB device controller, from the external device, a control signal corresponding to a user input of selecting a multimedia file from among a list of the plurality of multimedia files, the list of the plurality of multimedia files being displayed on the external device, the user input being received by the external device; cause the decoder unit to decode digital data of the multimedia file, and transmit, via the USB device controller, to the external device, the decoded digital data of the multimedia file and reproduction state information, such that the decoded digital data of the multimedia file is reproduced via the external device, and that the reproduction state information is displayed via the external device in relation to reproduction of the multimedia file, wherein the control unit is further configured to receive, via the USB device controller, from the external device, a control signal corresponding to a user input of pausing, and in response to receiving the control signal corresponding to the user input of pausing, cause the decoder unit to pause decoding the multimedia file, and transmit, via the USB device controller, the reproduction state information indicating pausing to the external device.