working on Needs-bisect, will update later.

We are unable to identify the specific issue in the provided video.Could you please provide the proper screen shot/ video with slow recording which would help us to triage the bug further.

Thank you.

I failed to reproduce the issue following the steps on Linux, Chrome 54 and 55 look identical to me.

If I modify the last step to exit the fullscreen mode by Esc key, there's a difference - the controls won't show under the mouse cursor in M54, but will in M55. So in M54 I'd have to click the video to show the controls after exiting fullscreen, while they will appear in M55 (and auto-hide shortly after).

I'm not sure what behavior is best and why this is a regression and not an improvement.

i'm a bit confused about the video vs. the bug description -- i can't see any click on the full screen button to exit the video.  looks like pressing escape.  some additional description about the regression would help me to understand the issue better.

during the transition into full screen, the bar transition looks a little different to me.  it might just be artifacts of trying to scrub the video with a touch screen on my chrome book (wfh), though.  there's an easing transition on the embedded => full screen transition which makes things confusing.

c#5: interesting -- i'd expect the M55 behavior, not the M54 behavior when exiting via escape.  but, i also have no idea which is better.

there were changes to MediaControls recently to support the overflow menu and downloads button, but i wouldn't expect that they'd impact when the bar is shown.

Retested above issue in latest canary 56.0.2897.0 and Dev build on Windows & Mac OS but issue is not reproducible. 
Thank you!

I tested on Dev&Canary. From the latest behavior, I think it has already been fixed, or could be WAI.

Please reopen if you disagree.