In today's Safari Technology Preview 68 Apple added VP8 support for WebRTC.
https://developer.apple.com/safari/technology-preview/release-notes/
WebRTC
Added VP8 support to WebRTC
Added support for IceCandidate stats
Added support for reporting “display composited video frames” through the VideoPlaybackQuality object
Added support for RTCPeerConnection.generateCertificate
Added support for RTCConfiguration.certificates
Implemented error handler of MediaRecorder