CORS violation for <track> element with data URI - WebVTT

• Component: Media
• Status: NEW ---

[Radosław Włodkowski]

Example URL:
https://jsfiddle.net/fixedmachine/ronaet82/2/

Steps to reproduce the problem:
1. Open given test site URL with <video> with <track> element with src specified as data URI with base64 encoded WebVTT subtitles.
2. The subtitles are not displayed.
3. There is an error log in console: Cross-origin text track load denied by Cross-Origin Resource Sharing policy.

What is the expected behavior?
The subtitles inside data URI are loaded, parsed and displayed correctly. No CORS violation is reported.

What went wrong?
CORS violation withhold subtitles data from loading and parsing, so they couldn't be displayed as expected.

Did this work before? No 

Does this work in other browsers? No. Chrome 41.0.2272.101, Opera 28.0.1750.48, Internet Explorer 11

The bug is present in all WebKit based browsers on all platforms: OS X, iOS (iPad, iPhone).

Similar issue was found in Firefox:
https://bugzilla.mozilla.org/show_bug.cgi?id=863485
but with current 36.0.4 version, data URIs for <track> elements seems to work fine.

Data URIs for <track> elements aren't working in IE11 too: CC menu is displayed with listed tracks, but subtitles aren't displayed. No errors are logged.

[Frédéric Wang (:fredw)]

There is probably a different (but maybe related) bug: we have a CORS violation when using local VTT files. Gecko can load local VTT files just fine.