An information processing system in which a content distribution server and a plurality of information processing devices (10, 18) are connected via a network; wherein a first information processing device operates as a client device and comprises: • a first communication unit configured to download content data from the content distribution server over the network; • a first storage unit configured to store content data downloaded from the content distribution server; • a first processing unit configured to play back the content data stored in the first storage unit; • a first instruction acquisition unit for acquiring a playback instruction; • a first detection unit configured to detect a status of downloading the content data; • a first notification unit configured to communicate the detected status of downloading to a second information processing device over the network via said first communication unit; and wherein the second information processing device operates as a host device and comprises: • a second communication unit configured to download the content data from the content distribution server over the network; • a second storage unit configured to store content data downloaded from the content distribution server; • a second processing unit configured to play back the content data stored in the second storage unit; • a second detection unit configured to detect a status of downloading the content data; • an acquisition unit configured to acquire the status of downloading communicated from the first information processing device; • a control unit configured to synchronize the playback of the content data in the first information processing device with the playback of the content data in the second information processing device based on the status of downloading of the first information processing device and the status of downloading of the second information processing device, said control unit comprising a last frame information derivation unit which refers to said first status of downloading so as to derive the frame number of the last frame that can be played in said first information processing device and refers to said second status of downloading so as to derive the frame number of the last frame that can be played in said second information processing device, and further derives the frame number of the last frame that can be played in synchronisation as the minimum of said two frame numbers; • a playback instruction generation unit for generating a playing instruction containing playback start time with reference to a clock shared by said first and second of the information processing devices, said playback start time being set on the basis of said minimum of said two frame numbers; and • a notification unit for communicating said generated playback instruction to said first information processing device. • a first communication unit configured to download content data from the content distribution server over the network; • a first storage unit configured to store content data downloaded from the content distribution server; • a first processing unit configured to play back the content data stored in the first storage unit; • a first instruction acquisition unit for acquiring a playback instruction; • a first detection unit configured to detect a status of downloading the content data; • a first notification unit configured to communicate the detected status of downloading to a second information processing device over the network via said first communication unit; • a second communication unit configured to download the content data from the content distribution server over the network; • a second storage unit configured to store content data downloaded from the content distribution server; • a second processing unit configured to play back the content data stored in the second storage unit; • a second detection unit configured to detect a status of downloading the content data; • an acquisition unit configured to acquire the status of downloading communicated from the first information processing device; • a control unit configured to synchronize the playback of the content data in the first information processing device with the playback of the content data in the second information processing device based on the status of downloading of the first information processing device and the status of downloading of the second information processing device, said control unit comprising a last frame information derivation unit which refers to said first status of downloading so as to derive the frame number of the last frame that can be played in said first information processing device and refers to said second status of downloading so as to derive the frame number of the last frame that can be played in said second information processing device, and further derives the frame number of the last frame that can be played in synchronisation as the minimum of said two frame numbers; • a playback instruction generation unit for generating a playing instruction containing playback start time with reference to a clock shared by said first and second of the information processing devices, said playback start time being set on the basis of said minimum of said two frame numbers; and • a notification unit for communicating said generated playback instruction to said first information processing device.