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[mediacapture-screen-share] Bring back constraints for downscaling, not selection filtering.

From: jan-ivar via GitHub <sysbot+gh@w3.org>
Date: Tue, 12 Sep 2017 00:21:34 +0000
To: public-media-capture@w3.org
Message-ID: <issues.opened-256879597-1505175685-sysbot+gh@w3.org>
jan-ivar has just created a new issue for https://github.com/w3c/mediacapture-screen-share:

== Bring back constraints for downscaling, not selection filtering. ==
@martinthomson In hindsight, an obstacle to implementing the spec is our current implementation in Firefox allows [passing in constraints](https://jsfiddle.net/jib1/dvyaq4pp/) to downscale the resolution and decimate frame rates from the very first frame. Our constraints do not filter the selection list at all.

We consider this a useful feature, since desktops tend to be of extremely large resolution, and their high frame-rates are overkill for most WebRTC use.

The spec currently disallows constraints on `getDisplayMedia`, except on subsequent calls to `track.applyConstraints` presumably.

This presumably means JS would need to expect the full-size full-frame-rate stream first, and then issue
```js
    await track.applyConstraints({width, height, frameRate})
```
on the video track before attaching it to a sink.

We're concerned this is resource intensive and inefficient, and may even cause failure in situations where returning the unscaled capture might fail where a downscaled version might not have failed.

We think this is a good reason to bring back constraints on `getDisplayMedia`. We'd need to craft strong wording to forbid UAs from using constraints to guide selection in any way.

Please view or discuss this issue at https://github.com/w3c/mediacapture-screen-share/issues/49 using your GitHub account
Received on Tuesday, 12 September 2017 00:21:28 UTC

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