Intent to ship: invalid <track kind> values behave like "metadata", not "subtitles"

[Aryeh Gregor]

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1269712

Relevant change in standards:
https://github.com/whatwg/html/issues/293, also maybe
https://www.w3.org/2015/10/28-htmlcue-minutes.html

Bugs filed against other UAs:
https://bugs.chromium.org/p/chromium/issues/detail?id=608772
https://bugs.webkit.org/show_bug.cgi?id=157311
https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/7426340/

Invalid values for <track kind> are currently treated as "subtitles"
by all UAs, pursuant to old specs. This means that if we want to add
any new values in the future, old UAs will treat them as subtitles,
which might result in undesired behavior. As such, several months
ago, the spec was changed to treat invalid values as "metadata", so
UAs will ignore unrecognized values. No UA has yet implemented the
new spec.

The risk in implementing this is that sites might be inadvertently
using invalid values right now and relying on the fact that they get
treated as "subtitles". I haven't done any telemetry or other
analysis at this point to gauge if this will be a problem in real
life.

If there are no objections, I intend to land this change on Sunday.

[Ralph Giles]

Sounds good. Thanks for the heads-up.

-r

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[Florin Mezei]

Do you still intend to do some analysis to see whether this will be a
problem in real life? We have somewhat of a history in shipping changes that
break compatibility, and then end up doing dot releases (in some cases).

[Aryeh Gregor]

On Thu, May 5, 2016 at 4:32 PM, Florin Mezei
<florin...@softvisioninc.eu> wrote:
> Do you still intend to do some analysis to see whether this will be a
> problem in real life? We have somewhat of a history in shipping changes that
> break compatibility, and then end up doing dot releases (in some cases).

I wasn't planning on putting in the work unless others thought it was
really necessary. In the linked bug, Boris wasn't sure. I don't know
anything about the feature's deployment, but I'd venture to guess that
it's not so widespread that the number of misuses would be too
significant in absolute terms.

[Aryeh Gregor]

On Sun, May 8, 2016 at 9:15 AM, Simon Pieters <sim...@opera.com> wrote:
> httparchive (494,168 pages):
>
> SELECT COUNT(*) AS num, REGEXP_EXTRACT(LOWER(body),
> r'<track\s(?:[^>]+\s)?kind\s*=\s*([a-z]+|["\'][^"\']+["\'])') as match
> FROM [httparchive:har.2016_04_15_chrome_requests_bodies]
> GROUP BY match
> ORDER BY num DESC
>
> Row num match
> 1 17616286 null
> 2 523 "subtitles"
> 3 108 "captions"
> 4 58 "metadata"
> 5 6 "subtitle"
> 6 6 'subtitles'
> 7 5 "thumbnails"
> 8 3 'captions'
> 9 1 "dotsub"
> 10 1 "${assettracktype}"
> 11 1 'subtitle'
>
>
> We could add "subtitle" as a new keyword if that turns out to be a problem.

Thanks for the data! Looks like we're talking on the order of 0.001%
of pages, so I think this can be safely landed.

[Simon Pieters]

VTTCueRender use counter for Chrome:

https://www.chromestatus.com/metrics/feature/timeline/popularity/410

httparchive (494,168 pages):

SELECT COUNT(*) AS num, REGEXP_EXTRACT(LOWER(body),
r'<track\s(?:[^>]+\s)?kind\s*=\s*([a-z]+|["\'][^"\']+["\'])') as match
FROM [httparchive:har.2016_04_15_chrome_requests_bodies]
GROUP BY match
ORDER BY num DESC

Row num match
1 17616286 null
2 523 "subtitles"
3 108 "captions"
4 58 "metadata"
5 6 "subtitle"
6 6 'subtitles'
7 5 "thumbnails"
8 3 'captions'
9 1 "dotsub"
10 1 "${assettracktype}"
11 1 'subtitle'


We could add "subtitle" as a new keyword if that turns out to be a problem.

--
Simon Pieters
Opera Software