I see that there is a -ifviewport autoplay experiment. I'm not entirely sure but it doesn't seem to be partial visibility. What does it exactly implement?

it requires that the entire element is visible, or at least fills the space it has if it's too wide / tall to fit.

I think we want visibility to be defined as partially visible (ie. at least 1x1 area). My understanding is that the consensus was about doing that.

renganathan@, do you confirm?

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/fafc5a0d288d30ad051e9269d6bdac1f79ed2f5b

commit fafc5a0d288d30ad051e9269d6bdac1f79ed2f5b
Author: liberato <liberato@chromium.org>
Date: Tue Apr 26 16:27:45 2016

Add partial viewport visibility check to autoplay experiment.

Adds -ifpartialviewport to require 1x1 overlap of the media element
with the viewport area, before autoplay is allowed.  This differs
from -ifviewport, which requires the element to be completely visible
within the viewport.

BUG= 605609 

Review URL: https://codereview.chromium.org/1921073002

Cr-Commit-Position: refs/heads/master@{#389802}

[modify] https://crrev.com/fafc5a0d288d30ad051e9269d6bdac1f79ed2f5b/third_party/WebKit/Source/core/html/AutoplayExperimentHelper.cpp
[modify] https://crrev.com/fafc5a0d288d30ad051e9269d6bdac1f79ed2f5b/third_party/WebKit/Source/core/html/AutoplayExperimentHelper.h