Intent to ship: MediaStreamTrack Content Hint
Harald Alvestrand
Contact emails
Explainer
None - see spec and demo.
Spec
https://w3c.github.io/mst-content-hint/
No tag review performed - minor feature.
Summary
This specification gives MediaStreamTracks (audio or video) an attribute that can be set by the application to give a hint about what aspects of the content are considered most important. This will be used by the platform to evaluate tradeoffs when quality of content has to be reduced - for instance when deciding frame rate or resolution when encoding video tracks for transmission or recording.
Example use cases include the ability to set “preserve detail” mode for screen capture content injected via a HDMI cable (which appears like a camera to the OS), and to set “preserve movement” mode for screencast inputs that are showing video.
Link to “Intent to Implement” blink-dev discussion
https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/gWp3xcyEDJM/JKOu68Y2BQAJ
Link to Origin Trial feedback summary
No origin trial performed.
Is this feature supported on all six Blink platforms (Windows, Mac, Linux, Chrome OS, Android, and Android WebView)?
Yes.
Demo link
https://webrtc.github.io/samples/src/content/capture/video-contenthint/
Debuggability
No special considerations.
Risks
Interoperability and Compatibility
This feature spec has been accepted by the WEBRTC W3C WG. Reception has not been enthusiastic, but mildly positive. Microsoft has indicated that they think something like this is definitely needed; Mozilla has debated the shape of the API, but did not put forward an alternate proposal.
Edge: No signals (that are quotable)
Firefox: No signals (https://github.com/mozilla/standards-positions/issues/101 filed)
Safari: No signals
Web developers: No signals
Ergonomics
No special considerations.
Activation
No special considerations. The feature is simple to take advantage of, easy to feature detect, and its introduction will have no negative impact on those who don’t use it.
Is this feature fully tested by web-platform-tests? Link to test suite results from wpt.fyi.
https://cs.chromium.org/chromium/src/third_party/WebKit/LayoutTests/fast/mediastream/MediaStreamTrack-contentHint.html?type=cs&q=contentHint+file:html&sq=package:chromium&g=0&l=29 will be migrated to web-platform-tests before the ship date.
This test exercises the interface, but doesn’t test the quality impact on the resulting transmission, since that is a far more complex test to write.
Entry on the feature dashboard
https://www.chromestatus.com/feature/5689466211532800
Chris Harrelson
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Philip Jägenstedt
I've sent https://github.com/tidoust/reffy/pull/121 which via some
roundabout processes and partially manual processes will cause an IDL
test for this to show up in wpt as well. Although that will add very
little on top of the MediaStreamTrack-contentHint.html which will be
upstreamed.
Alex Russell
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