This is a good app – GifLab - GIF Maker & Editor Review

I complained earlier about not being able to compile videos that are downloaded from places like Dropbox and Google Drive that weren't filmed on an iOS phone, but on further research realized it's Apple's fault since all other apps I tried wouldn't work. So people who complain about that here, direct your attention to Apple. Otherwise, it's a great app.
Review by Love Llamas on GifLab - GIF Maker & Editor.