1555849 - [webvtt] use `computeLine` to adjust cue's position when `snap-to-lines` is false

Status: RESOLVED FIXED

(Core :: Audio/Video: Playback, task, P2)

Description

[Alastor Wu [:alwu]]

According to the spec 7.2.6 [1], we should use computed line, not computed position [2].

[1] https://www.w3.org/TR/webvtt1/#ref-for-cue-computed-line-2
[2] https://searchfox.org/mozilla-central/rev/7556a400affa9eb99e522d2d17c40689fa23a729/dom/media/webvtt/vtt.jsm#691-694

Comment 1

[Alastor Wu [:alwu]]

Attachment: Bug 1555849 - part1 : use 'computeLine' to adjust cue's position when 'snap-to-lines' is false.

According to the spec 7.2.6 [1], we should use computed line, not computed position.

[1] https://www.w3.org/TR/webvtt1/#ref-for-cue-computed-line-2

Comment 2

[Alastor Wu [:alwu]]

Attachment: Bug 1555849 - part2 : enable wpt 'track-webvtt-non-snap-to-lines.html'.

As the video is 300*150, testing file would put the cue on the place which is 20% of video's height (30px) below.

The font size is defined as 5% of video's height (7.5px).

As the cue is left alignment, so we also have to set left=0.

In addition, there is no need to add padding.

Comment 3

[BugBot [:suhaib / :marco/ :calixte]]

Bugbug thinks this bug is a task, but please change it back in case of error.

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/8370f6e80cc8
part1 : use 'computeLine' to adjust cue's position when 'snap-to-lines' is false. r=heycam
https://hg.mozilla.org/integration/autoland/rev/04d4b4a547da
part2 : enable wpt 'track-webvtt-non-snap-to-lines.html'. r=heycam

Comment 5

[Web Platform Test Sync Bot (Matrix: #interop:mozilla.org)]

Created web-platform-tests PR https://github.com/web-platform-tests/wpt/pull/17331 for changes under testing/web-platform/tests

Comment 6

[Web Platform Test Sync Bot (Matrix: #interop:mozilla.org)]

Upstream web-platform-tests status checks passed, PR will merge once commit reaches central.

Comment 7

[Web Platform Test Sync Bot (Matrix: #interop:mozilla.org)]

Upstream PR merged

Comment 8

[Bogdan Tara[:bogdan_tara | bogdant]]

https://hg.mozilla.org/mozilla-central/rev/8370f6e80cc8
https://hg.mozilla.org/mozilla-central/rev/04d4b4a547da

Comment 9

[Alastor Wu [:alwu]]

Comment on attachment 9068873 [details]
Bug 1555849 - part1 : use 'computeLine' to adjust cue's position when 'snap-to-lines' is false.

ESR Uplift Approval Request

• If this is not a sec:{high,crit} bug, please state case for ESR consideration: This is a request from a confidential partner, because this issue affects the visual arrangement of subtitles.
• User impact if declined: Subtitles would be placed in the wrong place.
• Fix Landed on Version: 69
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): It only affects the final position of subtitles, to replace a value with another correct property while calculating the position.
• String or UUID changes made by this patch: No

Comment 10

[Ryan VanderMeulen [:RyanVM]]

Comment on attachment 9068873 [details]
Bug 1555849 - part1 : use 'computeLine' to adjust cue's position when 'snap-to-lines' is false.

Fixes a webvtt bug with a partner site. Approved for 68.1esr.

Comment 11

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/releases/mozilla-esr68/rev/68cd88e3c87e
https://hg.mozilla.org/releases/mozilla-esr68/rev/c2179726f2fa