Devices, methods, and graphical user interfaces for navigating, displaying, and editing media items with multiple display modes

An electronic device having a display and a touch-sensitive surface displays a representation of a media item that corresponds to a sequence of images including a representative image. In response to detecting a first input, the device displays an editing user interface that concurrently displays: a first area sequentially displaying images in the sequence of images at a first magnification; and a distinct second area including representations of the images at a second magnification less than the first magnification, and a user-adjustable representative image-selection affordance for selecting a new representative image. The device detects a second input moving the representative-image-selection affordance in the second area. The device displays in the first area an image corresponding to the representative-image-selection affordance current position in the second area.