Bisect info: 585321 (good) - 585333 (bad)
https://chromium.googlesource.com/chromium/src/+log/a0c12063..3f6c31f0?pretty=fuller
Suspecting r585322 = 321904d3d1c4675cfe9d25b1c30f528efcf869e4 = https://crrev.com/c/1161606 by kainino@chromium.org
"Add optimized path for YUV-to-WebGL, remove old path"
Landed in 70.0.3531.0

Kai, could you please triage?

Thanks for the bisect, I have a suspicion that my new code is losing the alpha channel at some point. Will investigate.

It's not my new code: skipping it does not fix the problem.

I think it's more likely that the code path I removed (which was supposed to be an optional acceleration path, and which I thought wasn't getting hit anymore) was handling it correctly, but the final fallback path is not.

https://crrev.com/c/1370499

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9d36bd3836883b3cbe7b51f3efba28956f4a976d

commit 9d36bd3836883b3cbe7b51f3efba28956f4a976d
Author: Kai Ninomiya <kainino@chromium.org>
Date: Tue Dec 11 20:09:24 2018

HTMLVideoElement: PaintCurrentFrame: default to SkBlendMode::kSrc

Bug:  912842 
Change-Id: I847e62edc50ccdf8d488843a8c4b7d04fd77b0c2
Reviewed-on: https://chromium-review.googlesource.com/c/1370499
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615635}
[modify] https://crrev.com/9d36bd3836883b3cbe7b51f3efba28956f4a976d/third_party/blink/renderer/core/html/media/html_video_element.cc
[modify] https://crrev.com/9d36bd3836883b3cbe7b51f3efba28956f4a976d/third_party/blink/renderer/core/html/media/html_video_element.h

Turns out this reproduces on Linux too with my regression test (though when I tested it the original test case did not repro). -OS-*

Test: https://github.com/KhronosGroup/WebGL/pull/2755

Requesting merge for #10 as it was a recent regression in M70.

Pls apply appropriate OSs label.

I thought OS-All was removed, I guess that changed again.

Anyway, this should impact all Blink platforms (all but iOS).

This bug requires manual review: M72 has already been promoted to the beta branch, so this requires manual review
Please contact the milestone owner if you have questions.
Owners: govind@(Android), kariahda@(iOS), djmm@(ChromeOS), abdulsyed@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8275ba81064cb9d524f3d3a414b45e7e0d78e851

commit 8275ba81064cb9d524f3d3a414b45e7e0d78e851
Author: Kai Ninomiya <kainino@chromium.org>
Date: Fri Dec 14 23:37:53 2018

HTMLVideoElement: PaintCurrentFrame: default to SkBlendMode::kSrc

Bug:  912842 
Change-Id: I847e62edc50ccdf8d488843a8c4b7d04fd77b0c2
Reviewed-on: https://chromium-review.googlesource.com/c/1370499
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#615635}(cherry picked from commit 9d36bd3836883b3cbe7b51f3efba28956f4a976d)
Reviewed-on: https://chromium-review.googlesource.com/c/1379214
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Cr-Commit-Position: refs/branch-heads/3626@{#375}
Cr-Branched-From: d897fb137fbaaa9355c0c93124cc048824eb1e65-refs/heads/master@{#612437}
[modify] https://crrev.com/8275ba81064cb9d524f3d3a414b45e7e0d78e851/third_party/blink/renderer/core/html/media/html_video_element.cc
[modify] https://crrev.com/8275ba81064cb9d524f3d3a414b45e7e0d78e851/third_party/blink/renderer/core/html/media/html_video_element.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4d1557e84992428767937e98808d3bbad915e53f

commit 4d1557e84992428767937e98808d3bbad915e53f
Author: James Darpinian <jdarpinian@chromium.org>
Date: Wed Dec 19 07:17:47 2018

Roll WebGL 5b6cbd7..a2b3563

https://chromium.googlesource.com/external/khronosgroup/webgl.git/+log/5b6cbd7..a2b3563

Bug: 849576,  809237 ,  911918 ,  angleproject:3012 
Bug: 913301,  912842 ,  913033 ,  563816 , 788439
Bug: angleproject:3033
Change-Id: I9b257afd69d26e75d1635633f556249583fdaa52
Cq-Include-Trybots: luci.chromium.try:win_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_angle_rel_ng;luci.chromium.try:win_angle_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/c/1383329
Commit-Queue: James Darpinian <jdarpinian@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#617754}
[modify] https://crrev.com/4d1557e84992428767937e98808d3bbad915e53f/DEPS
[modify] https://crrev.com/4d1557e84992428767937e98808d3bbad915e53f/content/test/gpu/gpu_tests/webgl2_conformance_expectations.py
[modify] https://crrev.com/4d1557e84992428767937e98808d3bbad915e53f/content/test/gpu/gpu_tests/webgl_conformance_revision.txt

Tried testing the issue on reported chrome version #71.0.3578.98 using Mac OS 10.13.6 and Ubuntu 17.10 by following below steps.

Steps:
=====
1.Launched chrome.
2.Extracted the file "WebM_Test.zip".
3.Opened "test.html".
4.Clicked on "play" button, observed that no audio and video being played.
5.Opened Devtools>Console and observed an error "Uncaught ReferenceError: THREE is not defined".
6.Tried with the "WebMAlphaVideoTexture.html", observed that no video and audio being played, error "Uncaught ReferenceError: THREE is not defined" in the console.
Note: Tested the same("WebM_Test.zip") in good build #70.0.3531.0 mentioned in comment#3 and observed the same behaviour as mentioned above.

Attached screencast and "WebMAlphaVideoTexture.html" for reference.
@reporter: Could you please review attached screencast and let us know if anything is being here. Requesting you to provide manual repro steps to reproduce the issue which helps us in verifying the fix.
Thanks.!

Deleted: 912842.mp4 1.0 MB

	912842.mp4 1.0 MB View Download

Deleted: WebMAlphaVideoTexture.html 1.6 KB

WebMAlphaVideoTexture.html 1.6 KB View Download

The following revision refers to this bug: 
https://chromium.googlesource.com/chromium/src.git/+/8275ba81064cb9d524f3d3a414b45e7e0d78e851

Commit: 8275ba81064cb9d524f3d3a414b45e7e0d78e851
Author: kainino@chromium.org
Commiter: kainino@chromium.org
Date: 2018-12-14 23:37:53 +0000 UTC

HTMLVideoElement: PaintCurrentFrame: default to SkBlendMode::kSrc

Bug:  912842 
Change-Id: I847e62edc50ccdf8d488843a8c4b7d04fd77b0c2
Reviewed-on: https://chromium-review.googlesource.com/c/1370499
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#615635}(cherry picked from commit 9d36bd3836883b3cbe7b51f3efba28956f4a976d)
Reviewed-on: https://chromium-review.googlesource.com/c/1379214
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Cr-Commit-Position: refs/branch-heads/3626@{#375}
Cr-Branched-From: d897fb137fbaaa9355c0c93124cc048824eb1e65-refs/heads/master@{#612437}

The original test case (for some reason) reproduces on Windows and Android but not Linux (I didn't try Mac).

However this test case DOES reproduce the bug on Linux:
https://www.khronos.org/registry/webgl/sdk/tests/conformance/textures/misc/texture-video-transparent.html
I suspect it would reproduce the bug on Mac too.

This test must be run with the Chrome flag --autoplay-policy=no-user-gesture-required .

kainino@, thank you for providing above test case and the fix is working as intended on M72 Beta# 72.0.3626.28 for Win 10, Mac OS X 10.13.6 and Linux platforms.