An information processing apparatus comprising: an acquisition unit configured to acquire contents in a first format including at least video data, subtitle data described in XML, and information for reproducing the subtitle data in synchronization with the video data, the first format being the MPEG Media Transport, MMT, format or MP4 format, the subtitle data including an XML document for displaying subtitles by use of image data, and the image data referred to in the XML document; a generation unit configured to generate auxiliary information for reproducing the subtitle data in synchronization with the video data when reproducing the contents in a second format, the second format being the MPEG-2 TS format, the auxiliary information including separation information used to separate the auxiliary information, the XML document, and the respective items of image data, the separation information including information indicating length of the auxiliary information, and information indicating number of the items of image data referred to in the XML document; and a multiplexing unit configured to add the auxiliary data to the subtitle data to generate subtitle data including the auxiliary information, and to packetize and multiplex the video data, and the subtitle data including the auxiliary information to generate contents in the second format, wherein the multiplexing unit is configured to generate, as packets of the subtitle data, a first packet and second packets subsequent to the first packet, a payload of the first packet including the auxiliary information and the XML document, and a payload of each second packet including a respective one of the items of image data referred to in the XML document. an acquisition unit configured to acquire contents in a first format including at least video data, subtitle data described in XML, and information for reproducing the subtitle data in synchronization with the video data, the first format being the MPEG Media Transport, MMT, format or MP4 format, the subtitle data including an XML document for displaying subtitles by use of image data, and the image data referred to in the XML document; a generation unit configured to generate auxiliary information for reproducing the subtitle data in synchronization with the video data when reproducing the contents in a second format, the second format being the MPEG-2 TS format, the auxiliary information including separation information used to separate the auxiliary information, the XML document, and the respective items of image data, the separation information including information indicating length of the auxiliary information, and information indicating number of the items of image data referred to in the XML document; and a multiplexing unit configured to add the auxiliary data to the subtitle data to generate subtitle data including the auxiliary information, and to packetize and multiplex the video data, and the subtitle data including the auxiliary information to generate contents in the second format, wherein the multiplexing unit is configured to generate, as packets of the subtitle data, a first packet and second packets subsequent to the first packet, a payload of the first packet including the auxiliary information and the XML document, and a payload of each second packet including a respective one of the items of image data referred to in the XML document.