Constant angular velocity or Standard Play discs supported several unique features such as freeze frame, variable slow motion and reverse. CAV discs were spun at a constant rotational speed (1800 rpm for 525 line and 1500 rpm for 625 line discs)[17] during playback, with one video frame read per revolution. In this mode, 54,000 individual frames (30 minutes of audio/video) could be stored on a single side of a CAV disc. Another unique attribute to CAV was to reduce the visibility of crosstalk from adjacent tracks, since on CAV discs any crosstalk at a specific point in a frame is simply from the same point in the next or previous frame. CAV was used less frequently than CLV, and reserved for special editions of feature films to highlight bonus material and special effects. One of the most intriguing advantages of this format was the ability to reference every frame of a film directly by number, a feature of particular interest to film buffs, students and others intrigued by the study of errors in staging, continuity and so on.