To prevent piracy of films, the standard drill of film distribution is to have a movie first released through movie theaters (theatrical window), on average approximately 16 and a half weeks, before having it released to Blu-Ray and DVD (entering its video window). During the theatrical window, digital versions of films are often transported in data storage devices by couriers rather than by data transmission. The data can be encrypted, with the key being made to work only at specific times in order to prevent leakage between screens. Coded Anti-Piracy marks can be added to films to identify the source of illegal copies and shut them down. As a result of these measures, the only versions of films available for piracy during the theatrical window are usually "cams" made by video recordings of the movie screens, which are of inferior quality compared to the original film version.