MSE-in-Workers: Track enable/selection change behavior needs clarity #281
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wolenetz
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to wolenetz/media-source
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Jun 26, 2021
Makes sourceBuffer {A/V/T}Track attribute language for MSE-in-Worker
normative (formerly was in a non-normative note).
BIG TODO/in-progress: Updates initialization segment received algorithm to create
cross-context track clones on track creation.
BIG TODO: Updates removeSourceBuffer language to remove cross-context
track clones on SourceBuffer removal from its parent media source.
BIG TODO: Updates the "Changes to selected/enabled track state" section
to describe cross-context track clone changes. See also w3c#281.
Also fixes a couple minor typos.
wolenetz
added a commit
to wolenetz/media-source
that referenced
this issue
Jun 29, 2021
Makes sourceBuffer {A/V/T}Track attribute language for MSE-in-Worker
normative (formerly was in a non-normative note).
Updates MSE-in-Worker version of the initialization segment received
algorithm to create cross-context track clones on track creation, and to
conditionally update the cross-context media element's readyState.
BIG TODO: Updates removeSourceBuffer language to remove cross-context
track clones on SourceBuffer removal from its parent media source.
BIG TODO: Updates the "Changes to selected/enabled track state" section
to describe cross-context track clone changes. See also w3c#281.
Also fixes a couple minor typos.
wolenetz
added a commit
to wolenetz/media-source
that referenced
this issue
Jun 29, 2021
Makes sourceBuffer {A/V/T}Track attribute language for MSE-in-Worker
normative (formerly was in a non-normative note).
Updates MSE-in-Worker version of the initialization segment received
algorithm to create cross-context track clones on track creation, and to
conditionally update the cross-context media element's readyState.
Updates MSE-in-Worker version of removeSourceBuffer language to remove
relevant cross-context track mirrors on SourceBuffer removal from its
parent media source.
BIG TODO: Updates the "Changes to selected/enabled track state" section
to describe cross-context track clone changes. See also w3c#281.
Also fixes a couple minor typos.
wolenetz
added a commit
to wolenetz/media-source
that referenced
this issue
Jun 29, 2021
Makes sourceBuffer {A/V/T}Track attribute language for MSE-in-Worker
normative (formerly was in a non-normative note).
Updates MSE-in-Worker version of the initialization segment received
algorithm to create cross-context track clones on track creation, and to
conditionally update the cross-context media element's readyState.
Updates MSE-in-Worker version of removeSourceBuffer language to remove
relevant cross-context track mirrors on SourceBuffer removal from its
parent media source.
Updates the "Changes to selected/enabled track state" section to
describe Window/DedicatedWorker track state changes. See also w3c#281.
Also fixes a couple minor typos.
wolenetz
added a commit
to wolenetz/media-source
that referenced
this issue
Jun 30, 2021
Makes sourceBuffer {A/V/T}Track attribute language for MSE-in-Worker
normative (formerly was in a non-normative note).
Updates MSE-in-Worker version of the initialization segment received
algorithm to create cross-context track clones on track creation, and to
conditionally update the cross-context media element's readyState.
Updates MSE-in-Worker version of removeSourceBuffer language to remove
relevant cross-context track mirrors on SourceBuffer removal from its
parent media source.
Updates the "Changes to selected/enabled track state" section to
describe Window/DedicatedWorker track state changes. See also w3c#281.
Also fixes a couple minor typos.
|
Requesting this be discussed at Sept 14 Media WG meeting. |
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MSE-in-Workers feature issue is #175
The "Changes to selected/enabled track state" section makes sense in the REC v1 spec for Window-only MSE and HTMLMediaElement.
This issue tracks figuring out what to do with such state management if MSE is in a DedicatedWorker, while the HTMLMediaElement remains in Window.
Assuming apps might need information about tracks in either context, and similarly may wish to change the state of them, how best can this be done in the specification?
Scenario:
Simultaneous track selection of different video tracks in each of the Window (media element) and DedicatedWorker (MSE): These changes can affect what the extended HTMLMediaElement's seekable and buffered attributes return:
seekableandbufferedare conditioned upon information from the current activeSourceBuffers list.It's probable that this scenario will not be solved by forcing all implementations to make such changes atomically[*]. While some do (like Chrome's prototype implementation), the solution might be a non-normative note that apps may need to be aware of how potential delays in buffered, seekable, etc information resulting from scenarios like this might occur. A potential handler might need to round-trip the necessary information on the application side with message passing there.
[*] Internally, a message posting/handling mechanism is described by the MSE-in-Worker spec (in my upcoming PR for the initial spec draft, there will be a "Cross-context communication model" section describing that mechanism as well as allowance for implementations to use potentially faster locking and shared memory). In Chrome's prototype implementation so far (apart from this track stuff which is not yet fully implemented in worker), micro-locking is used for most of the communication, rather than the potentially slower message passing.
[edited the last paragraph for clarity June 25 2021]
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