A method for calculating file size of video data stored in a digital video recorder (DVR) device includes storing video data having segments and index data including file size information associated with segments of the video data. The method also includes enabling an interval to export a selected portion of video data among the video data stored in the DVR device to a storage unit. The A method further includes reading the index data including the file size information associated with the video data stored in the DVR device and obtaining file size information from the read the index data in response to the enabled interval In addition, calculating a size of video data to be exported based on the obtained file size information.