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Issue 633690 link

Starred by 9 users
Status: Assigned
Owner:
sriram...@samsung.com
Cc:
f...@opera.com
█ johnpallett@chromium.org
█ guohuideng@chromium.org
█ k2.nagar...@samsung.com
█ joeyparrish@chromium.org
█ pangu@google.com
█ halliwell@chromium.org
wolenetz@chromium.org
Components:
EstimatedDays: ----
NextAction: ----
OS: All
Pri: 3
Type: Feature



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Chrome does not support VTTCue lineAlign and positionAlign attributes

Project Member Reported by ismena@google.com, Aug 2 2016 
UserAgent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.82 Safari/537.36

Steps to reproduce the problem:
1. Go to console in Chrome Developer Tools
2. Instantiate a VTTCue object (e. g. cue = new VTTCue(1,2,'');)
3. Take a look at cue's properties and/or type "cue.lineAlign", "cue.positionAlign". The properties are undefinied.

What is the expected behavior?
The attributes are supported. 

Reference:
According to https://w3c.github.io/webvtt/#vttcue VTTCue class has positionAlign (enum PositionAlignSetting { "line-left", "center", "line-right", "auto" };) and lineAlign (enum LineAlignSetting { "start", "center", "end" };) settings.

What went wrong?
The attributes are supported.

Did this work before? No 

Chrome version: 52.0.2743.82  Channel: stable
OS Version: 
Flash Version: Shockwave Flash 22.0 r0

Comment 1 by joeyparrish@chromium.org, Aug 2 2016

Cc: joeyparrish@chromium.org
Labels: -OS-Linux OS-All

Comment 2 by joeyparrish@chromium.org, Aug 2 2016

Cc: johnpallett@chromium.org foolip@chromium.org pangu@google.com

Comment 3 by joeyparrish@chromium.org, Aug 2 2016

Cc: wolenetz@chromium.org

Comment 4 by foolip@chromium.org, Aug 2 2016

Cc: f...@opera.com
Components: Blink>Media>Track
Did you want to achieve some specific rendering that requires lineAlign and/or positionAlign?

Comment 5 by joeyparrish@chromium.org, Aug 2 2016

Labels: -Pri-2 Pri-3
Shaka Player is an open-source player library that implements text support by parsing WebVTT and feeding VTTCues to the browser.  We don't have a specific rendering to achieve, but our users may.

We recently added support for parsing these parts of the WebVTT spec, but with the caveat that Chromium doesn't yet support those attributes: https://github.com/google/shaka-player/issues/469

We aren't implying that this should be top priority for Chrome, but filed this issue to make sure that this part of the VTT spec didn't slip through the cracks indefinitely.  Lowered priority accordingly.

Comment 6 by f...@opera.com, Aug 3 2016

Status: Available (was: Unconfirmed)
IIRC, we intentionally did not implement support for these two properties/settings (the VTTCue settings parser has comments [1] about skipping relevant steps in the parsing algorithm.) The reason was essentially the same as foolip's question in c#4 =)

If someone wants to implement this though (preferably accompanied by a use-case) I'd be happy to help w/ reviews and whatnot. So, setting to available for now.

[1] https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/html/track/vtt/VTTCue.cpp?q=VTTCue&sq=package:chromium&l=988
Project Member

Comment 7 by sheriffbot@chromium.org, Aug 5 2016

Labels: Hotlist-Google

Comment 8 by zcorpan@gmail.com, Feb 22 2017 

These are supported in Gecko.

I think the use case is basically better control in positioning things.

See http://w3c.github.io/webvtt/#example-0c2976c9 for an example.

00:00:00.000 --> 00:00:04.000 position:10%,line-left align:left size:35%
Where did he go?

Without position-align you need to set position to some value that doesn't correspond to what the author actually intends:

00:00:00.000 --> 00:00:04.000 position:27.5% align:left size:35%
Where did he go?

27.5% here is: intended position (10%) + size/2 (35%/2). Not intuitive.

Having this also makes the mapping from other subtitle formats to WebVTT (and back) more straightforward.

Comment 9 by f...@opera.com, Feb 27 2017 

@zcorpan: Are there any tests (yet)? ;-)

Maybe more importantly, how much stuff will we break (and how badly)? I guess fixing this would also help with/fix  issue 652745 .

Comment 10 by zcorpan@gmail.com, Feb 28 2017 

Fixing rendering tests to match the current spec is not done yet.

I don't know how to measure compat impact of WebVTT rendering. But we don't have interop now...

Comment 11 by foolip@chromium.org, Mar 3 2017 

Adding these attributes itself shouldn't have much potential to break stuff, right? Or is there some change in default behavior that should go with it?

Comment 12 by f...@opera.com, Mar 3 2017 

Just adding the attributes should be fine - but not very useful. There are changes in the rendering section though that I can not tell by a glance if they break stuff though. (Changes to computed values mostly.) I could run my implementation through our existing tests I guess =). (I don't think our rendering test coverage is great though...)

Comment 13 by zcorpan@gmail.com, Mar 3 2017 

I think we should have a plan to add this in the parser, API, and rendering, ideally all shipping in the same milestone. Supporting only the API would be bad for feature detection.

Comment 14 by k2.nagar...@samsung.com, Nov 8 2017 

started working on this issue.

pushed WIP patch
https://chromium-review.googlesource.com/c/chromium/src/+/756142

Comment 15 by foolip@chromium.org, Nov 21 2017

Cc: -foolip@chromium.org

Comment 16 by rbyers@chromium.org, Nov 23 2017

Cc: k2.nagar...@samsung.com
Owner: sriram...@samsung.com
Status: Started (was: Available)
Intent to ship: https://groups.google.com/a/chromium.org/d/msg/blink-dev/KRAyvMD4QZs/ABBp-5aLBAAJ

Assigned to srirama.m since k2.nagaraju does not appear to have edit bugs access yet.

Edge bug: https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/11025599/
Project Member

Comment 17 by bugdroid1@chromium.org, Dec 21 2017 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2c1d466d78db6df8b4c9fbe37ac5af1cb135bf34

commit 2c1d466d78db6df8b4c9fbe37ac5af1cb135bf34
Author: k2.nagaraju <k2.nagaraju@samsung.com>
Date: Thu Dec 21 10:03:52 2017

Support VTTCue.positionAlign and lineAlign for WebVTT

Implement VTTCue.[positionAlign and lineAlign] for WebVTT
Updated parsing logic
Exposed DOM API's
Updated Layout algorithm
Updated test expected results

Bug: 633690
Change-Id: I49970c068c53b462243ba8c7f314261b0e6455ce
Reviewed-on: https://chromium-review.googlesource.com/756142
Commit-Queue: srirama chandra sekhar <srirama.m@samsung.com>
Reviewed-by: srirama chandra sekhar <srirama.m@samsung.com>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Reviewed-by: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#525659}
[delete] https://crrev.com/b3ed17839d4177142aeab4a832f42ad21d18da3f/third_party/WebKit/LayoutTests/external/wpt/webvtt/api/VTTCue/constructor-expected.txt
[delete] https://crrev.com/b3ed17839d4177142aeab4a832f42ad21d18da3f/third_party/WebKit/LayoutTests/external/wpt/webvtt/api/VTTCue/lineAlign-expected.txt
[delete] https://crrev.com/b3ed17839d4177142aeab4a832f42ad21d18da3f/third_party/WebKit/LayoutTests/external/wpt/webvtt/api/VTTCue/positionAlign-expected.txt
[delete] https://crrev.com/b3ed17839d4177142aeab4a832f42ad21d18da3f/third_party/WebKit/LayoutTests/external/wpt/webvtt/api/interfaces-expected.txt
[delete] https://crrev.com/b3ed17839d4177142aeab4a832f42ad21d18da3f/third_party/WebKit/LayoutTests/external/wpt/webvtt/parsing/file-parsing/tests/settings-position-expected.txt
[add] https://crrev.com/2c1d466d78db6df8b4c9fbe37ac5af1cb135bf34/third_party/WebKit/LayoutTests/external/wpt/webvtt/rendering/cues-with-video/processing-model/track-cue-rendering-position-align-rtl-center-ref.html
[add] https://crrev.com/2c1d466d78db6df8b4c9fbe37ac5af1cb135bf34/third_party/WebKit/LayoutTests/external/wpt/webvtt/rendering/cues-with-video/processing-model/track-cue-rendering-position-align-rtl-center.html
[add] https://crrev.com/2c1d466d78db6df8b4c9fbe37ac5af1cb135bf34/third_party/WebKit/LayoutTests/external/wpt/webvtt/rendering/cues-with-video/processing-model/track-cue-rendering-position-align-rtl-line-left-ref.html
[add] https://crrev.com/2c1d466d78db6df8b4c9fbe37ac5af1cb135bf34/third_party/WebKit/LayoutTests/external/wpt/webvtt/rendering/cues-with-video/processing-model/track-cue-rendering-position-align-rtl-line-left.html
[add] https://crrev.com/2c1d466d78db6df8b4c9fbe37ac5af1cb135bf34/third_party/WebKit/LayoutTests/external/wpt/webvtt/rendering/cues-with-video/processing-model/track-cue-rendering-position-align-rtl-line-right-ref.html
[add] https://crrev.com/2c1d466d78db6df8b4c9fbe37ac5af1cb135bf34/third_party/WebKit/LayoutTests/external/wpt/webvtt/rendering/cues-with-video/processing-model/track-cue-rendering-position-align-rtl-line-right.html
[modify] https://crrev.com/2c1d466d78db6df8b4c9fbe37ac5af1cb135bf34/third_party/WebKit/LayoutTests/media/track/captions-webvtt/captions-snap-to-lines-not-set.vtt
[modify] https://crrev.com/2c1d466d78db6df8b4c9fbe37ac5af1cb135bf34/third_party/WebKit/LayoutTests/media/track/track-cue-rendering-position-auto-rtl-expected.html
[modify] https://crrev.com/2c1d466d78db6df8b4c9fbe37ac5af1cb135bf34/third_party/WebKit/LayoutTests/virtual/stable/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/2c1d466d78db6df8b4c9fbe37ac5af1cb135bf34/third_party/WebKit/LayoutTests/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/2c1d466d78db6df8b4c9fbe37ac5af1cb135bf34/third_party/WebKit/Source/core/html/track/vtt/VTTCue.cpp
[modify] https://crrev.com/2c1d466d78db6df8b4c9fbe37ac5af1cb135bf34/third_party/WebKit/Source/core/html/track/vtt/VTTCue.h
[modify] https://crrev.com/2c1d466d78db6df8b4c9fbe37ac5af1cb135bf34/third_party/WebKit/Source/core/html/track/vtt/VTTCue.idl
[modify] https://crrev.com/2c1d466d78db6df8b4c9fbe37ac5af1cb135bf34/third_party/WebKit/Source/core/layout/LayoutVTTCue.cpp
[modify] https://crrev.com/2c1d466d78db6df8b4c9fbe37ac5af1cb135bf34/third_party/WebKit/Source/core/layout/LayoutVTTCue.h

Comment 18 by sriram...@samsung.com, Jan 11 2018

Status: Fixed (was: Started)

Comment 19 by fbeaufort@chromium.org, Jan 12 2018 

I'm currently playing with new VTTCue lineAlign and positionAlign attributes at https://beaufortfrancois.github.io/sandbox/media/video-cue.html and I'm having hard time understand what is the expected behaviour.

Changing cue.lineAlign value doesn't change anything for instance.

Firefox and Chrome implementations differ when updating cue.lineAlign and cue.positionAlign as well.

Comment 20 by f...@opera.com, Jan 12 2018 

Did you set .snapToLines to false? IIRC, lineAlign will only have an effect in that case.
Project Member

Comment 21 by bugdroid1@chromium.org, Feb 22 2018 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ce7509393d9dd7ec49b8e0fd10d94959288a7caf

commit ce7509393d9dd7ec49b8e0fd10d94959288a7caf
Author: Philip Jägenstedt <foolip@chromium.org>
Date: Thu Feb 22 14:35:06 2018

Revert "Support VTTCue.positionAlign and lineAlign for WebVTT"

This reverts commit 2c1d466d78db6df8b4c9fbe37ac5af1cb135bf34.

Reason for revert:  https://crbug.com/814710 

Conflicts with https://chromium-review.googlesource.com/836576 resolved.

Original change's description:
> Support VTTCue.positionAlign and lineAlign for WebVTT
>
> Implement VTTCue.[positionAlign and lineAlign] for WebVTT
> Updated parsing logic
> Exposed DOM API's
> Updated Layout algorithm
> Updated test expected results
>
> Bug: 633690
> Change-Id: I49970c068c53b462243ba8c7f314261b0e6455ce
> Reviewed-on: https://chromium-review.googlesource.com/756142
> Commit-Queue: srirama chandra sekhar <srirama.m@samsung.com>
> Reviewed-by: srirama chandra sekhar <srirama.m@samsung.com>
> Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
> Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
> Reviewed-by: Fredrik Söderquist <fs@opera.com>
> Cr-Commit-Position: refs/heads/master@{#525659}

TBR=fs@opera.com,chrishtr@chromium.org,srirama.m@samsung.com,foolip@chromium.org,k2.nagaraju@samsung.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 633690
Change-Id: Ib9f0b3dd1a4b679076ec55ec635337551f8b8806
Reviewed-on: https://chromium-review.googlesource.com/931481
Commit-Queue: Philip Jägenstedt <foolip@chromium.org>
Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Cr-Commit-Position: refs/heads/master@{#538429}
[add] https://crrev.com/ce7509393d9dd7ec49b8e0fd10d94959288a7caf/third_party/WebKit/LayoutTests/external/wpt/webvtt/api/VTTCue/constructor-expected.txt
[add] https://crrev.com/ce7509393d9dd7ec49b8e0fd10d94959288a7caf/third_party/WebKit/LayoutTests/external/wpt/webvtt/api/VTTCue/lineAlign-expected.txt
[add] https://crrev.com/ce7509393d9dd7ec49b8e0fd10d94959288a7caf/third_party/WebKit/LayoutTests/external/wpt/webvtt/api/VTTCue/positionAlign-expected.txt
[add] https://crrev.com/ce7509393d9dd7ec49b8e0fd10d94959288a7caf/third_party/WebKit/LayoutTests/external/wpt/webvtt/api/interfaces-expected.txt
[add] https://crrev.com/ce7509393d9dd7ec49b8e0fd10d94959288a7caf/third_party/WebKit/LayoutTests/external/wpt/webvtt/parsing/file-parsing/tests/settings-position-expected.txt
[delete] https://crrev.com/ad431f78b0f527f8c512b7b7632120e895c2f8f9/third_party/WebKit/LayoutTests/external/wpt/webvtt/rendering/cues-with-video/processing-model/track-cue-rendering-position-align-rtl-center-ref.html
[delete] https://crrev.com/ad431f78b0f527f8c512b7b7632120e895c2f8f9/third_party/WebKit/LayoutTests/external/wpt/webvtt/rendering/cues-with-video/processing-model/track-cue-rendering-position-align-rtl-center.html
[delete] https://crrev.com/ad431f78b0f527f8c512b7b7632120e895c2f8f9/third_party/WebKit/LayoutTests/external/wpt/webvtt/rendering/cues-with-video/processing-model/track-cue-rendering-position-align-rtl-line-left-ref.html
[delete] https://crrev.com/ad431f78b0f527f8c512b7b7632120e895c2f8f9/third_party/WebKit/LayoutTests/external/wpt/webvtt/rendering/cues-with-video/processing-model/track-cue-rendering-position-align-rtl-line-left.html
[delete] https://crrev.com/ad431f78b0f527f8c512b7b7632120e895c2f8f9/third_party/WebKit/LayoutTests/external/wpt/webvtt/rendering/cues-with-video/processing-model/track-cue-rendering-position-align-rtl-line-right-ref.html
[delete] https://crrev.com/ad431f78b0f527f8c512b7b7632120e895c2f8f9/third_party/WebKit/LayoutTests/external/wpt/webvtt/rendering/cues-with-video/processing-model/track-cue-rendering-position-align-rtl-line-right.html
[modify] https://crrev.com/ce7509393d9dd7ec49b8e0fd10d94959288a7caf/third_party/WebKit/LayoutTests/media/track/captions-webvtt/captions-snap-to-lines-not-set.vtt
[modify] https://crrev.com/ce7509393d9dd7ec49b8e0fd10d94959288a7caf/third_party/WebKit/LayoutTests/media/track/track-cue-rendering-position-auto-rtl-expected.html
[modify] https://crrev.com/ce7509393d9dd7ec49b8e0fd10d94959288a7caf/third_party/WebKit/LayoutTests/virtual/stable/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/ce7509393d9dd7ec49b8e0fd10d94959288a7caf/third_party/WebKit/LayoutTests/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/ce7509393d9dd7ec49b8e0fd10d94959288a7caf/third_party/WebKit/Source/core/html/track/vtt/VTTCue.cpp
[modify] https://crrev.com/ce7509393d9dd7ec49b8e0fd10d94959288a7caf/third_party/WebKit/Source/core/html/track/vtt/VTTCue.h
[modify] https://crrev.com/ce7509393d9dd7ec49b8e0fd10d94959288a7caf/third_party/WebKit/Source/core/html/track/vtt/VTTCue.idl
[modify] https://crrev.com/ce7509393d9dd7ec49b8e0fd10d94959288a7caf/third_party/WebKit/Source/core/layout/LayoutVTTCue.cpp
[modify] https://crrev.com/ce7509393d9dd7ec49b8e0fd10d94959288a7caf/third_party/WebKit/Source/core/layout/LayoutVTTCue.h

Comment 22 by f...@opera.com, Feb 22 2018

Status: Assigned (was: Fixed)
Project Member

Comment 23 by bugdroid1@chromium.org, Feb 23 2018

Labels: merge-merged-3325
The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4c63e960cad94fdd004b911964765381079912d2

commit 4c63e960cad94fdd004b911964765381079912d2
Author: Philip Jägenstedt <foolip@chromium.org>
Date: Fri Feb 23 19:42:07 2018

Revert "Support VTTCue.positionAlign and lineAlign for WebVTT"

This reverts commit 2c1d466d78db6df8b4c9fbe37ac5af1cb135bf34.

Reason for revert:  https://crbug.com/814710 

Conflicts with https://chromium-review.googlesource.com/836576 resolved.

Original change's description:
> Support VTTCue.positionAlign and lineAlign for WebVTT
>
> Implement VTTCue.[positionAlign and lineAlign] for WebVTT
> Updated parsing logic
> Exposed DOM API's
> Updated Layout algorithm
> Updated test expected results
>
> Bug: 633690
> Change-Id: I49970c068c53b462243ba8c7f314261b0e6455ce
> Reviewed-on: https://chromium-review.googlesource.com/756142
> Commit-Queue: srirama chandra sekhar <srirama.m@samsung.com>
> Reviewed-by: srirama chandra sekhar <srirama.m@samsung.com>
> Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
> Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
> Reviewed-by: Fredrik Söderquist <fs@opera.com>
> Cr-Commit-Position: refs/heads/master@{#525659}

TBR=fs@opera.com,chrishtr@chromium.org,srirama.m@samsung.com,foolip@chromium.org,k2.nagaraju@samsung.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 633690
Change-Id: Ib9f0b3dd1a4b679076ec55ec635337551f8b8806
Reviewed-on: https://chromium-review.googlesource.com/931481
Commit-Queue: Philip Jägenstedt <foolip@chromium.org>
Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#538429}(cherry picked from commit ce7509393d9dd7ec49b8e0fd10d94959288a7caf)
Reviewed-on: https://chromium-review.googlesource.com/935341
Cr-Commit-Position: refs/branch-heads/3325@{#575}
Cr-Branched-From: bc084a8b5afa3744a74927344e304c02ae54189f-refs/heads/master@{#530369}
[add] https://crrev.com/4c63e960cad94fdd004b911964765381079912d2/third_party/WebKit/LayoutTests/external/wpt/webvtt/api/VTTCue/constructor-expected.txt
[add] https://crrev.com/4c63e960cad94fdd004b911964765381079912d2/third_party/WebKit/LayoutTests/external/wpt/webvtt/api/VTTCue/lineAlign-expected.txt
[add] https://crrev.com/4c63e960cad94fdd004b911964765381079912d2/third_party/WebKit/LayoutTests/external/wpt/webvtt/api/VTTCue/positionAlign-expected.txt
[add] https://crrev.com/4c63e960cad94fdd004b911964765381079912d2/third_party/WebKit/LayoutTests/external/wpt/webvtt/api/interfaces-expected.txt
[add] https://crrev.com/4c63e960cad94fdd004b911964765381079912d2/third_party/WebKit/LayoutTests/external/wpt/webvtt/parsing/file-parsing/tests/settings-position-expected.txt
[delete] https://crrev.com/dd3ffe08423aa031745588df3ad24c2bae9992ad/third_party/WebKit/LayoutTests/external/wpt/webvtt/rendering/cues-with-video/processing-model/track-cue-rendering-position-align-rtl-center-ref.html
[delete] https://crrev.com/dd3ffe08423aa031745588df3ad24c2bae9992ad/third_party/WebKit/LayoutTests/external/wpt/webvtt/rendering/cues-with-video/processing-model/track-cue-rendering-position-align-rtl-center.html
[delete] https://crrev.com/dd3ffe08423aa031745588df3ad24c2bae9992ad/third_party/WebKit/LayoutTests/external/wpt/webvtt/rendering/cues-with-video/processing-model/track-cue-rendering-position-align-rtl-line-left-ref.html
[delete] https://crrev.com/dd3ffe08423aa031745588df3ad24c2bae9992ad/third_party/WebKit/LayoutTests/external/wpt/webvtt/rendering/cues-with-video/processing-model/track-cue-rendering-position-align-rtl-line-left.html
[delete] https://crrev.com/dd3ffe08423aa031745588df3ad24c2bae9992ad/third_party/WebKit/LayoutTests/external/wpt/webvtt/rendering/cues-with-video/processing-model/track-cue-rendering-position-align-rtl-line-right-ref.html
[delete] https://crrev.com/dd3ffe08423aa031745588df3ad24c2bae9992ad/third_party/WebKit/LayoutTests/external/wpt/webvtt/rendering/cues-with-video/processing-model/track-cue-rendering-position-align-rtl-line-right.html
[modify] https://crrev.com/4c63e960cad94fdd004b911964765381079912d2/third_party/WebKit/LayoutTests/media/track/captions-webvtt/captions-snap-to-lines-not-set.vtt
[modify] https://crrev.com/4c63e960cad94fdd004b911964765381079912d2/third_party/WebKit/LayoutTests/media/track/track-cue-rendering-position-auto-rtl-expected.html
[modify] https://crrev.com/4c63e960cad94fdd004b911964765381079912d2/third_party/WebKit/LayoutTests/virtual/stable/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/4c63e960cad94fdd004b911964765381079912d2/third_party/WebKit/LayoutTests/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/4c63e960cad94fdd004b911964765381079912d2/third_party/WebKit/Source/core/html/track/vtt/VTTCue.cpp
[modify] https://crrev.com/4c63e960cad94fdd004b911964765381079912d2/third_party/WebKit/Source/core/html/track/vtt/VTTCue.h
[modify] https://crrev.com/4c63e960cad94fdd004b911964765381079912d2/third_party/WebKit/Source/core/html/track/vtt/VTTCue.idl
[modify] https://crrev.com/4c63e960cad94fdd004b911964765381079912d2/third_party/WebKit/Source/core/layout/LayoutVTTCue.cpp
[modify] https://crrev.com/4c63e960cad94fdd004b911964765381079912d2/third_party/WebKit/Source/core/layout/LayoutVTTCue.h

Comment 24 by halliwell@chromium.org, Feb 27 2018

Cc: guohuideng@chromium.org halliwell@chromium.org

Comment 25 by guohuideng@google.com, Feb 27 2018 

1. the "alignment" setting is not needed, "position" and "width" together would have all the flexibility the user need.

for example, "position = 30, alignment = center, width = 40" is equivalent to
"position = 10, alignment = left, width = 40"

So for example, we can specify that the "position" is always refereed to the "left". "position" is default to "50" so when not specified it's located in center.

2. There are users that put each line in a cue box. So change the way the cue box's location always has potential to break things.

-- just my 2 cents

Comment 26 by guohuideng@google.com, Feb 27 2018 

Correction: I meant that one possible solution is to leave the "position" refer to "center" (I wrongly said "left")(or what the old implementation was). 

====
I think lots of authors of the webvtt content used their own way to align things and they use old implementations to verify their work. Then they were happy with what they saw they released the content. Then later if the locations of subtitles changes, it will be surprise to them, especially if it breaks things.

-- just my 2 cents

Comment 27 by guohuideng@chromium.org, Apr 25 2018 

I have created a new issue to request a change in the specification that "lineAlignment" and "positionAlignment" shouldn't be implemented

https://bugs.chromium.org/p/chromium/issues/detail?id=836630
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