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[webrtc-pc] Deciding on resolutions with scaleResolutionDownBy

From: Andreas Pehrson via GitHub <sysbot+gh@w3.org>
Date: Tue, 29 Aug 2017 12:12:25 +0000
To: public-webrtc@w3.org
Message-ID: <issues.opened-253634376-1504008733-sysbot+gh@w3.org>
Pehrsons has just created a new issue for https://github.com/w3c/webrtc-pc:

== Deciding on resolutions with scaleResolutionDownBy ==
The spec mentions constraints on the value of `scaleResolutionDownBy` but not how it applies when actually scaling video frames.

I have a couple of cases in mind where it is unclear what resolution will be sent over the wire:

- Common input `640x480`, odd `scaleResolutionDownBy` `x9.0`.
  - You can't scale to `71.111x53.333`
- Odd input (say canvas or application sharing), e.g., `705x529`, `scaleResolutionDownBy` `x2.0`.
  - You can't scale to `78.333x58.778`
- The encoder doesn't handle scaling to certain resolutions
  - webrtc.org requires that all layers have identical aspect ratio, see [1], so a scaling factor where the result has to be rounded (like the two above) need a bit more massaging to be accepted. Not sure about other implementations or hardware encoders.

[1] http://searchfox.org/mozilla-central/rev/b318c7dca7392bd16c0b11929f55b1be133f0b31/media/webrtc/trunk/webrtc/modules/video_coding/codecs/vp8/simulcast_encoder_adapter.cc#62

Please view or discuss this issue at https://github.com/w3c/webrtc-pc/issues/1564 using your GitHub account
Received on Tuesday, 29 August 2017 12:12:21 UTC

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