Regarding the scope of the fix involved in this relaunch, it removes visibility of the new handle attribute from the main/Window context (and updates test expectations, accordingly.) While that change alone would fix the regression, it risks potential for unexpected exception in future if that attribute were ever exposed again on the main/Window context. Therefore, both the spec and implementation involved in this relaunch also remove the ability to throw NotSupportedError exception by this attribute's getter.
With the net change versus the previous launch being specific to fixing this regression, and with the relaunch CL also including base::Feature guards for the two blink RuntimeEnabled features for MSE-in-Workers, I believe the risk of relaunch causing respin to be small even if some similar scope of regression were found after the feature reached stable. Matt On Wed, Sep 28, 2022 at 12:40 PM Matthew Wolenetz <wolen...@chromium.org> wrote: > Per previous LGTMs on this, the feature launched in M105: > https://chromium-review.googlesource.com/c/chromium/src/+/3795560 > Unfortunately, both the MSE spec and Chromium implementation for this > feature included logic which regressed some media playback sites, and the > regression was found late after the feature reached stable in M105. > The launch was reverted from 105 (and 106-108 also have had this feature > reverted explicitly back to experimental). > > The regression was due to the MediaSource object's new handle attribute > being: > > 1. Visible on both main/Window and on Dedicated Worker contexts (not > just the latter), and > 2. Throwing NotSupportedError exception if read from on a context > (main/Window, in this case) where the implementation does not support using > a MediaSourceHandle for attaching the MediaSource object owned by that > context. > > The specific MSE spec language involved in this regression (from > https://github.com/w3c/media-source/pull/306): > > "If the implementation does not support creating a handle for this > MediaSource, then throw a NotSupportedError exception and abort these > steps.NOTE Implementations MAY choose to only allow handle creation for > MediaSource objects in a DedicatedWorkerGlobalScope, as a minimum > requirement for enabling attachment of such a MediaSource object to an > HTMLMediaElement." > > > Uncaught by myself nor multiple reviewers (except partially by > cas...@chromium.org, who asked about precedent for throwing exceptions in > attribute getters > <https://chromium-review.googlesource.com/c/chromium/src/+/3750140/comment/201a43a2_85dfa17f/>), > there was a pre-existing behavior pattern in at least one older version of > a media playback javascript library (video.js) that enumerated all > MediaSource object attributes, including reading from them and obtaining an > unexpected exception on reading this new handle attribute on the > main/Window context. > > Also uncaught by myself nor reviewers was the lack of "flag-guarding" of > this feature (it only had blink runtime enabled features, not corresponding > base::Features), so the revert in M105 stable of the previous launch > required a binary respin. > > The MSE spec has been updated to replace this regressing logic > <https://github.com/w3c/media-source/pull/317>, and the corresponding > Chromium implementation update, addition of flag-guards, and relaunch to > stable (in current M108 milestone) is in code-review now > <https://chromium-review.googlesource.com/c/chromium/src/+/3910706> and > is pending further LGTMs on this thread. > > Please review for relaunch. I expect I'll need 3 LGTMs to proceed with > landing the relaunch CL > <https://chromium-review.googlesource.com/c/chromium/src/+/3910706>. > > Thank you, > Matt > > > On Mon, Aug 1, 2022 at 10:59 AM 'Joe Medley' via blink-dev < > blink-dev@chromium.org> wrote: > >> Gang, >> >> NOTE: Requested desktop and Android ship milestone: 105 (The 'edit >>> estimated milestones' link from chromestatus didn't result in such ability >>> to edit, so I'm adding this request explicitly here.) >> >> >> I'm looking into this and will report back. Has anyone else noticed this >> problem? >> >> Joe >> Joe Medley | Technical Writer, Chrome DevRel | jmed...@google.com | >> 816-678-7195 <(816)%20678-7195> >> *If an API's not documented it doesn't exist.* >> >> >> On Mon, Aug 1, 2022 at 8:52 AM Mike Taylor <miketa...@chromium.org> >> wrote: >> >>> LGTM3 >>> >>> On 8/1/22 8:05 AM, Yoav Weiss wrote: >>> >>> LGTM2 >>> >>> On Fri, Jul 29, 2022 at 12:40 AM slightlyoff via Chromestatus < >>> admin+slightly...@cr-status.appspotmail.com> wrote: >>> >>>> LGTM1 >>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "blink-dev" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to blink-dev+unsubscr...@chromium.org. >>>> To view this discussion on the web visit >>>> https://groups.google.com/a/chromium.org/d/msgid/blink-dev/000000000000eea04c05e4e53819%40google.com >>>> <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/000000000000eea04c05e4e53819%40google.com?utm_medium=email&utm_source=footer> >>>> . >>>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "blink-dev" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to blink-dev+unsubscr...@chromium.org. >>> To view this discussion on the web visit >>> https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAL5BFfWsqYRjB%3DqCuu4UxHzEa%2B%2B2SqkDJdE8W8sUNCnS%2BwoH5w%40mail.gmail.com >>> <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAL5BFfWsqYRjB%3DqCuu4UxHzEa%2B%2B2SqkDJdE8W8sUNCnS%2BwoH5w%40mail.gmail.com?utm_medium=email&utm_source=footer> >>> . >>> >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "blink-dev" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to blink-dev+unsubscr...@chromium.org. >>> To view this discussion on the web visit >>> https://groups.google.com/a/chromium.org/d/msgid/blink-dev/91d78e87-3241-0719-eb2a-a7e8d21afd0b%40chromium.org >>> <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/91d78e87-3241-0719-eb2a-a7e8d21afd0b%40chromium.org?utm_medium=email&utm_source=footer> >>> . >>> >> -- >> You received this message because you are subscribed to the Google Groups >> "blink-dev" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to blink-dev+unsubscr...@chromium.org. >> To view this discussion on the web visit >> https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAJUhtG8EH2E1y33qLPJr3xdp8ZT1z1T98mCQ9bJ4WeBn19BOsQ%40mail.gmail.com >> <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAJUhtG8EH2E1y33qLPJr3xdp8ZT1z1T98mCQ9bJ4WeBn19BOsQ%40mail.gmail.com?utm_medium=email&utm_source=footer> >> . >> > -- You received this message because you are subscribed to the Google Groups "blink-dev" group. 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