Thanks, I was on the team that did Ultra HDR at Google so I was curious if it was being used here. Didn't see anything in the code though so that makes sense.
Something I've been wondering about with the Ultra HDR format, is why did you add the Google GContainer? As far as I can tell, it doesn't do anything that the MPF part doesn't already.
I didn't actually work on the format, just happened to be on the same team. My guess would be that it's related to compatibility with the places the format need to render (android, chrome, photos) or possibly necessary to preserve edit metadata.