FrameStep is a video player designed to allow you to step through videos one frame at a time.
Originally designed for Animators and VFX artists, FrameStep can be used by anyone for video review.
One screen controls are provided for basic operations like play/pause, frame ahead/back, and timeline scrubbing. Tapping the four quadrants of the video gives larger targets. With an attached keyboard, additional controls are available, like speed control in addition to the more common ones listed above.
Videos maybe be opened though its interface, via the Files app, or through the Share sheet in another app. FrameStep does not read from your photos -- you must save videos from Photos to Files to view ones created on you iPad / iPhone.