How can any device that supports JPG support this Ultra HDR format if it is not exactly to JPG specifications? They mention they embed more data into the file than just a typical JPG so how can software that previous supported JPG know what to do with it?
It sounds like it's backwards compatible so places that don't support the new format will simply get an SDR version of the photo and I'm sure Google will try to get everyone to support this new type of jpg.