WebRTC-SVC (Scalable Video Coding)

[dontcallmedom]

I'm requesting a TAG re-review of WebRTC Scalable Video Coding.

WebRTC Scalable Video Coding allows to use the capabilities of modern video codecs to combine several video quality into a single encoded stream sent via WebRTC to an endpoint that can then dispatch the right substream to the different parties based on their receiving capabilities.

• Explainer¹ (minimally containing user needs and example code): https://github.com/w3c/webrtc-svc/blob/master/explainer.md
• Specification URL: https://www.w3.org/TR/2023/WD-webrtc-svc-20230417/
• Tests: https://github.com/web-platform-tests/wpt/tree/master/webrtc-svc
• User research: N/A
• Security and Privacy self-review²: https://w3c.github.io/webrtc-svc/#privacy and https://w3c.github.io/webrtc-svc/#security
• GitHub repo (if you prefer feedback filed there): https://github.com/w3c/webrtc-svc/
• Primary contacts (and their relationship to the specification):
  • Bernard Aboba @aboba (WG co-chair, spec editor)
• Organization(s)/project(s) driving the specification: W3C WebRTC Working Group
• Key pieces of existing multi-stakeholder review or discussion of this specification: https://github.com/w3c/webrtc-svc/issues
• External status/issue trackers for this specification (publicly visible, e.g. Chrome Status):
  • RTCRtpEncodingParameters.scalabilityMode WebKit/standards-positions#103
  • https://chromestatus.com/feature/5769626174619648

Further details:

• I have reviewed the TAG's Web Platform Design Principles
• Relevant time constraints or deadlines: [please provide]
• The group where the work on this specification is currently being done: W3C WebRTC Working Group
• Major unresolved issues with or opposition to this specification: N/A

You should also know that there was a previous review of this specification 4 years ago: #396

We'd prefer the TAG provide feedback as (please delete all but the desired option):

🐛 open issues in our GitHub repo for each point of feedback

[johnathan79717]

The Security and Privacy self-review link is invalid. I think you mean https://w3c.github.io/webrtc-svc/#privacy and https://w3c.github.io/webrtc-svc/#security.

[Orphis]

We had a TAG review already done in #396 , is it not sufficient?

[aboba]

@Orphis I had the same question. The only major change in the API from the last TAG review was the use of Media Capabilities API instead of getCapabililties().

[dontcallmedom]

#396 is 4 years old; so this request is to check that the intervening changes (in this spec and in the platform in general) don't warrant new feedback

[dontcallmedom]

@torgo any ETA on this review? We're trying to assess when we might be ready to request CR

[hober]

@Orphis I had the same question. The only major change in the API from the last TAG review was the use of Media Capabilities API instead of getCapabililties().

It looks like almost everything in the spec has changed since our last review.

[torgo]

Hi folks -

Thanks for sending us this review. Given what @adoba wrote above concerning the changes and the fact that Media Capabilities API itself enjoys multi-stakeholder support, we'd like to close this review. However, it looks to us like a lot of additional changes were made to the spec. @dontcallmetom can you confirm that this is the only substantive change?

[dontcallmedom]

This isn't the only substantive change, although it's probably the most platform-impacting one.

The list of non-editorial pull requests merged since the last TAG review can be classified as follows:

• refinement to list of SVC modes: Add missing modes to the table w3c/webrtc-svc#84 Addition of mode L3T1_KEY to table w3c/webrtc-svc#82 Remove references to L1T2h and L1T3h w3c/webrtc-svc#71 Add L1T1 scalability mode` w3c/webrtc-svc#51 Case Sensitivity of scalability modes w3c/webrtc-svc#33 Scalability Mode Table revision w3c/webrtc-svc#39
• privacy impact of exposing capabilities (and its delegation to Media Capabilities): Remove extension to getCapabilities() in favour of MediaCapabilities w3c/webrtc-svc#76 Remove RTCRtpReceiver.getCapabilities() w3c/webrtc-svc#54 Hardware/software leaks w3c/webrtc-svc#26
• API clarification of behavior and error handling of reading and setting SVC modes: Add Behavior section w3c/webrtc-svc#64 Refine error conditions for use of 'S' modes w3c/webrtc-svc#86 Substitute spatialScalabilty for referenceScaling w3c/webrtc-svc#62 Changing the interpretation if referenceScaling is absent w3c/webrtc-svc#56 Clarify behavior of setParameters() w3c/webrtc-svc#67 Clarify behavior of getParameters() w3c/webrtc-svc#69 Update getParameters() to not return the default scalabilityMode w3c/webrtc-svc#79
• clarifications in Browser/SFU negotiation: Clarify SDP negotiation and Decoder Compliance w3c/webrtc-svc#53 Browser/SFU negotiation w3c/webrtc-svc#35

[torgo]

Hi @dontcallmedom thanks for that clarification. On that basis we're happy to see this move forward. Thanks for bringing to us!