Hey James - we officially support:
Images: JPEG, PNG, TIFF, BMP
Videos: MP4, MKV, AVI, MOV, OGG, GIF
(GIFs get treated as videos, but if they aren’t animated they only generate one API call)
The four image formats are listed at the very bottom of the Developer Guide. Not sure if the rest of these will work with the API but good to know that they're working with the demo!