# KSVC scalability modes for VP9

**URL:** <https://mediasoup.discourse.group/t/ksvc-scalability-modes-for-vp9/2802>\
**Category:** mediasoup libraries\
**Created:** [May 18, 2021, 2:41pm UTC](https://mediasoup.discourse.group/t/ksvc-scalability-modes-for-vp9/2802 "2021-05-18T14:41:51Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![vpalmisano](https://yyz2.discourse-cdn.com/free1/user_avatar/mediasoup.discourse.group/vpalmisano/32/43_2.png) [@vpalmisano](https://mediasoup.discourse.group/u/vpalmisano)\
**Post date:** [May 18, 2021, 2:41pm UTC](https://mediasoup.discourse.group/t/ksvc-scalability-modes-for-vp9/2802/1 "2021-05-18T14:41:51Z")

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I’m going more in deep with the Dependency Descriptor extension support required for AV1 and also enabled for VP9 ([1196318 - chromium - An open-source project to help move the web forward. - Monorail](https://bugs.chromium.org/p/chromium/issues/detail?id=1196318#c8)), and seems that the default scalabilityMode value used in the mediasoup demo (S3T3\_KEY) is not included in the draft specifications ([Scalable Video Coding (SVC) Extension for WebRTC](https://w3c.github.io/webrtc-svc/#scalabilitymodes*)).  
Is there something that I’m missing about this? Thanks

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**Author:** ![ibc](https://yyz2.discourse-cdn.com/free1/user_avatar/mediasoup.discourse.group/ibc/32/1540_2.png) [@ibc](https://mediasoup.discourse.group/u/ibc)\
**Post date:** [May 18, 2021, 2:57pm UTC](https://mediasoup.discourse.group/t/ksvc-scalability-modes-for-vp9/2802/2 "2021-05-18T14:57:16Z")

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AFAIR `S3T3_KEY` was in a previous version of the draft. Anyway, mediasoup threats “S” and “L” the same way.