Video player controls not visible on bright background
When there is white (or very bright) background in a video it is impossible to see the controls (play button, scrub/progress bar), the white icons should be combined with a darker color to avoid this.
IMHO the best option with regards to general look&feel of the OS would be to use a dark, semi-transparent rectangle as contrasting background of the progress bar; and a dark, semi-transparent circle for the play button in the center.
Example screenshot below - which is not all too bright, yet the elements are barely recognizable, even on a desktop monitor. One the phone, in daylight, there's no chance.