I am using Ubuntu 16.04 LTS (64-bit) on an AMD FX-60 (dual core 2.6 GHz). It is pretty slow by today's standards, and it took some time to find a video player which wouldn't sputter. I tested about 6 players and only SMPlayer played my 1080P H.264 iphone videos well on this system. I have SMPlayer version 21.1.0 (revision 9475) installed.
I noticed that there is a +-90 deg. rotation feature, but not a 180 deg. feature. Would you be willing to add a 180 deg. feature? Unfortunately, the iphone rotational information which gets saved to the .mov video file is not always correct. So while it can be tempting to use other software which auto rotates the videos based on the saved rotational information, even that software will get it wrong if iPhone saves it wrong.
Much appreciated.