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Bug 26345 - [MSE] order of activeSourceBuffers underspecified
Summary: [MSE] order of activeSourceBuffers underspecified
Status: RESOLVED FIXED
Alias: None
Product: HTML WG
Classification: Unclassified
Component: Media Source Extensions (show other bugs)
Version: unspecified
Hardware: PC All
: P2 normal
Target Milestone: CR
Assignee: Aaron Colwell
QA Contact: HTML WG Bugzilla archive list
URL:
Whiteboard:
Keywords:
Depends on:
Blocks:
 
Reported: 2014-07-15 23:02 UTC by Jer Noble
Modified: 2014-07-24 20:13 UTC (History)
3 users (show)

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Attachments

Description Jer Noble 2014-07-15 23:02:06 UTC
2.1 Attributes, activeSourceBuffers
"activeSourceBuffers of type SourceBufferList, readonly
Contains the subset of sourceBuffers that are providing the selected video track, the enabled audio track(s), and the "showing" or "hidden" text track(s)."

The order of entries in the SourceBufferList are underspecified. Intuitively, activeSourceBuffers should have the same order as sourceBuffers, but a naive implementation may order them depending on what SourceBuffer reached a "Add the SourceBuffer to activeSourceBuffers" step first.
Comment 1 Aaron Colwell 2014-07-24 17:46:54 UTC
Why does order matter here? I don't particulary object to mandating that the order match sourceBuffers, but I don't really understand why it matters. Won't the application always have to manually inspect the lists if sourceBuffers.length != activeSourceBuffers.length? Why let the application treat the == case differently?
Comment 2 Jer Noble 2014-07-24 17:50:47 UTC
(In reply to Aaron Colwell from comment #1)
> Why does order matter here? 

Well, honestly, because WebKit's implementation fails some of the proposed W3C Media Source testsuite tests which expect a particular order.  Specifically, the mediasource-buffered.html will fail if the order of activeSourceBuffers is not the same as sourceBuffers.
Comment 3 Jer Noble 2014-07-24 17:53:09 UTC
Also, the general trend toward array-like objects in W3C specs, and particularly in the Text Track specs, has been to give those arrays an explicit, deterministic order.
Comment 4 Aaron Colwell 2014-07-24 17:58:44 UTC
Ok. Fair enough. I'll make the change. Thanks for your input.
Comment 5 Aaron Colwell 2014-07-24 20:13:34 UTC
Change committed.
https://dvcs.w3.org/hg/html-media/rev/13056a200b38