Video pictures pattern detection

Some embodiments of the invention provide a media-editing application that performs frame rate conversion detection on a video. For a video that has been converted from one frame rate and format to another frame rate and format, the application detects the conversion method that has been used in the conversion of the video. Some embodiments perform this frame rate conversion detection by detecting patterns of repeating fields and/or frames in a video sequence created by the different conversion processes. Some embodiments compute (i) a frame difference value for each consecutive frames, (ii) a correlation score for the first and second fields of each frame, and (iii) a correlation score for the second field of each frame and the first field of a succeeding frame. Frame difference values are compared with each other to detect repeated frames and correlation scores are compared with each other to detect repeated fields.