Hi there, yeah, a TXT as a manual is a good idea, will try to add it on a future update.
The input can be one or multiple video/gif/PNG
If you want to do a PNG sequence, put all PNG in a single folder and select a single PNG from that folder. The application will try to sort all files in a sequence, so the name should be something like 0001 0002 0003 etc
For now spritesheets don't work, perhaps in the future.
If you have any more questions feel free to ask in here.