over to mlamouri@ and cc:foolip@ for any potential poster changes. First frame of the video is black, so it shouldn't be the first frame showing up.

So this is a regression between M52 and M54? I don't recall any recent changes to poster, but a bisect should quickly find the truth :)

This isn't Android specific. I can reproduce the same problem on desktop Chrome (Linux).

Working on M53 (53.0.2785.101)
Not working on M54 (54.0.2816.0)

It seems to be a regression from https://codereview.chromium.org/2169343002 according to `git bisect` and reverting commit b76fc4469acf4c44336dd8d42d1e127c8823d08b on top of tree fixes the issue.

Twitter doesn't use a poster and instead shows an image. I guess, they were relying on the previous behaviour?

Can we revert the patch ASAP, we are planning a Beta Release soon.

This is broken in M54 and works fine in M53. Please revert the patch ASAP. This is blocking the scheduled Beta Release tomorrow.

You are probably looking for a change made after 407434 (known good), but no later than 407435 (first known bad).

CHANGELOG URL:
==============  https://chromium.googlesource.com/chromium/src/+log/48c3ff1de4496dc724db0b604c6ed5cc1b20c60c..b76fc4469acf4c44336dd8d42d1e127c8823d08b

Working as intended in - 54.0.2840.27 (Official Build) beta (64-Bit), MAC 10.11

Reverted patch: https://codereview.chromium.org/2332373003/

Has been reverted/merged, see 628968.

This was fixed by Twitter, fwiw:

.InlineMedia {
	border-radius:.4rem;
	-webkit-mask-image:url(data:image/png;base64,R0lGODlhAQABAIAAAP///////yH5BAEKAAEALAAAAAABAAEAAAICRAEAOw==);
	-webkit-mask-repeat:repeat;
	overflow:hidden
}

Gecko ran into similar issues and we asked twitter to update (and they did very quickly).

issue no on w3c github: 
https://github.com/w3c/csswg-drafts/issues/599