In this paper we propose a method for the automatic detection of the true aspect ratio of digital video, by detecting the presence and width of horizontal and vertical black bars, also known as letterbox and pillarbox effects. If active format description (AFD) metadata is not present, the proposed method can be used to identify the right AFD and associate it to the video content. In the case AFD information is present, the method can be used to verify its correctness and to correct it in case of error. Additionally, the proposed method also allows to detect if relevant information (as broadcaster logos and hard subtitles) is merged within the black bars and, in the case of subtitles, is able to extract it from the bars and dislocate it to the active picture area (allowing the letterbox removal).