1. A method of transmitting stereoscopic video, comprising: generating a base image and an additional image, the base image being one of a left image and a right image, the additional image including a reduced left image corresponding to the left image and a reduced right image corresponding to the right image and having predetermined image format comprising one of a side-by-side format and a top-and-bottom format; generating a base image stream, corresponding to the base image, and an additional image stream, corresponding to the additional image, by coding the base image and the additional image, respectively; generating single stream information by multiplexing the base image stream and the additional image stream; and transmitting image information including the single stream information, wherein a stereoscopic service includes at least one of a first service and a second service, wherein the first service allows the stereoscopic video to be generated using both the base image and the one reduced image not corresponding to the base image, wherein the second service allows the stereoscopic video to be generated using both the reduced left image and the reduced right image of the additional image.