Re: Revision of Scalable Video Coding Extension for WebRTC

I have deleted the "S" modes from the table, and have added "L3" modes that, while not included in the list of AV1 predefined scalability modes might conceivably be useful.

________________________________
From: Bernard Aboba <Bernard.Aboba@microsoft.com>
Sent: Wednesday, October 10, 2018 9:12:29 AM
To: Sergio Garcia Murillo
Cc: public-webrtc@w3.org
Subject: Re: Revision of Scalable Video Coding Extension for WebRTC

In WebRTC 1.0, simulcast streams can have arbitrary scaling ratios, whereas the modes without inter-layer dependencies only support fixed ratios.  So I’m not sure what value the “S” modes add.  Might make sense to delete them from the table.

On Oct 10, 2018, at 03:11, Sergio Garcia Murillo <sergio.garcia.murillo@gmail.com<mailto:sergio.garcia.murillo@gmail.com>> wrote:

I have also one further question, are the modes not using interlayer dependency really interesting for us?

>From the AV1 spec, when no inter layer dependency is used the second (and next) spatial layer does not use its corresponding base layer as a reference. I understand that this is interesting from an encoder perspective, so can produce both spatial layers with the same encoder, but it wouldn't make sense for us to send them over the same ssrc, but on different simulcasts stream instead.

Best regards
Sergio

On 10/10/2018 0:49, Bernard Aboba wrote:

The proposed SVC Extension for WebRTC has been revised in order to reduce the complexity for developers wishing to support Scalable Video Coding.


The new proposal relies on the concept of "scalability modes" utilized in [AV1] as well as other SVC codecs.


The revised proposal is here:

https://rawgit.com/aboba/webrtc-sim/master/svc.html<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Frawgit.com%2Faboba%2Fwebrtc-sim%2Fmaster%2Fsvc.html&data=02%7C01%7CBernard.Aboba%40microsoft.com%7Ced005a77963d47a3312508d62ecb7292%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636747848708398638&sdata=doh9MweqlBHlsh0CNDhkeZiiyR4pEL3WQfhcyAsLBps%3D&reserved=0>


Some slides describing the proposal and the logic behind it are available here:

https://docs.google.com/presentation/d/113UL2TpcXaYOmLw2GeDPjTqDeu2J5OWaqo_SYvzQvC4<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdocs.google.com%2Fpresentation%2Fd%2F113UL2TpcXaYOmLw2GeDPjTqDeu2J5OWaqo_SYvzQvC4&data=02%7C01%7CBernard.Aboba%40microsoft.com%7Ced005a77963d47a3312508d62ecb7292%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636747848708408643&sdata=zOQHz5TdX%2FfhryJE4%2BZs5Gy2gK2dMNThQUdzZmhFahY%3D&reserved=0>


[AV1]
AV1 Bitstream and Decoding Process Specification<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Faomediacodec.github.io%2Fav1-spec%2Fav1-spec.pdf&data=02%7C01%7CBernard.Aboba%40microsoft.com%7Ced005a77963d47a3312508d62ecb7292%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636747848708408643&sdata=r6qC36b7i1vh68ciZsjZjNGB2iyZjgVftUkDdYpMt4E%3D&reserved=0>. Peter de Rivaz; Jack Haughton. Alliance for Open Media. June 25, 2018. URL: https://aomediacodec.github.io/av1-spec/av1-spec.pdf<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Faomediacodec.github.io%2Fav1-spec%2Fav1-spec.pdf&data=02%7C01%7CBernard.Aboba%40microsoft.com%7Ced005a77963d47a3312508d62ecb7292%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636747848708418653&sdata=159iYruSHPTeC%2BTuv0ayoMaU%2BMYC3waKU2XdwnjkcyQ%3D&reserved=0>