Learned about exporting buffers from Core Image to Core Video to export video
Really liked the simplicity of the inline help overlay
Apply and animate shaders on an image or video.
Easily set up a pipeline of Core Image video effects over a base video or image
Manipulate effects by binding effect parameters to touches
Animate and loop changes to effect parameters
Sequence changes to effect parameters with a step sequencer
Easily inspect the result of a subset of the pipeline
Export animation to camera roll
Use an animation as the base material of a new effect pipeline
Had a lot of fun playing with this on the subway.
Limiting the number of effects in the pipeline keeps the user experience simple; allowing the user to "chain" pipelines keeps the tool powerful.
Easily recording changes with a camera-like interface is fun and easy, but tough to make a clean loop. A quantized sequencer helps to keep things clean.
The interface for binding parameters to touch input is clunky: it's slow to configure, and doesn't clearly communicate the structure of the bindings. (I implemented the simplest thing, and designed a whole bunch of alternatives. I think there were a couple of slightly better alternatives in the pile; but, in general, I think "patching interfaces" is a tough problem on a small screen.)
I was idealizing linear bindings from touch position to parameter changes, because I believed direct control would allow the user to get different styles of animation by learning to "perform" those styles (e.g. get a bouncy animation by learning how to gesture bouncily). This is not really possible. Figuring out a way to define non-linear mappings between input and controlled parameters would help make more dynamic animations.
Create "album art" videos from sound, text, and images.
I made this as a utility to support another video app I was working on. In that app, the user could add a soundtrack by importing sound from a previously-captured video. I used this feature in tandem with iOS's screen recording feature to grab sound from Spotify or YouTube to put into my videos; but it was tough to find a specific sound by scanning my camera roll. Using this app to add "album art" to those soundtrack videos, I could easily find the sounds I wanted.
Inline help overlay
Arrange text and background image to create album art
Export as video to camera roll
Felt good to turn my camera roll into a slightly more functional file system :)