If I play a video in Photos it always appears in maximum size, I do not see any option to adjust the appearance to the size and pixel count of the video file. I have many old small video files, and of course they do not look very good in full screen mode on a 27” iMac. Any solutions at the moment ? Or waiting for Photos 2.0 ?
Have you tried making the Photos window smaller? For me videos play entirely inside the Photos window and they scale to the size of the window. If you keep the Photos window filling the entire screen then videos will scale up to it.
Thomas