It would actually be great if you could change the main image in the video. Sometimes you just miss the best moment by a fraction of a second. But that would require that all images in this 'video' (jpg sequence) use the full resolution.If I had to guess, the phone is somewhat smart about it. The actual "video" part is stored as a lower resolution because of the fact that it won't ever be uploaded elsewhere and so it can stay to the resolution of the screen of the device its on. Then you can likely still have HDR and all that active o the still image. Just a hunch.