Re: [webrtc-pc] Add video latency constrainable property (#2109)

@kuddai thanks for clarifying! Unfortunately, constrainable properties on remote tracks is severely under-specified, with only a [single paragraph](https://w3c.github.io/webrtc-pc/#mediatracksupportedconstraints-mediatrackcapabilities-mediatrackconstraints-and-mediatracksettings).

That paragraph only really talks about "`MediaTrackSettings`" being "populated with members". I find it hard to interpret more from that than "there should be observable read-only settings". There's no requirement or mention of what should happen when e.g. *applyConstraints()* is called.

Now, Media Capture's ["the model"](https://w3c.github.io/mediacapture-main/getusermedia.html#the-model-sources-sinks-constraints-and-settings) section does imagine how this *could* work. But that section is non-normative, imaginative (automatic renegotiation from *applyConstraints*??), and somewhat outdated. It's even missing some key illustrations on this very topic. As I recall, our appetite for *action-at-a-distance* waned over the years.

In other words, an implementation today that always rejects `receiver.track.applyConstraints()` with `OverconstrainedError`, like Firefox does, would likely be considered compliant, I think.

Making this section stronger would likely require new consensus, and probably not start with *latency*.

That said, I'd probably take a PR that removes *latency* from the list of exclusions.

> Currently you have option to only increase latency for the audio track

Where do you see that?

If this is important to you, I would start with collecting support for the use cases and problem first, and then look for the right API second: Is the best place for this control knob really on every track clone, or the receiver, the stream (which is a synchronization group after all) or even the pc itself?

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Received on Friday, 1 March 2019 00:06:36 UTC