![]() ![]() Unlike Simulcast which sends multiple streams with redundant information and packetization overhead, SVC aims to provide a more efficient implementation by encoding layers of information representing different bitrates within a single stream. SVC is a not a new concept – it was originally introduced as part of H264/MPEG-4 and was later standardized there 2005. Scalable Video Coding (SVC) refers to the codec capability of producing several encoded layers within the same bit stream. Scalable Video Coding (SVC) is a more sophisticated approach to minimize this overhead while maintaining the benefits of the SFU model. However, simulcast does have some drawbacks – its extra independently encoded streams result in extra bandwidth overhead and CPU usage. This means the SFU can also selectively forward different packets to provide different frame rates of each quality depending on the available peer bandwidth. Fortunately when enabling simulcast in Chrome you get support for temporal scalability automatically (explained below). ![]() Simulcast requires the endpoints send two or three versions of the same stream with different resolutions/qualities so that the SFU server can forward a different one to each destination. For the past couple of years, Chrome’s unofficial support for simulcast and temporal scalability within the VP8 codec provided one of the best ways to implement a WebRTC SFU. SFU’s were particularly popular for WebRTC. This was largely due to its scalable and relatively inexpensive server-side architecture. Then the Selective Forwarding Unit (SFU) model based on forwarding packets without any re-encoding began to become very popular. ![]() MCU’s transcode (fully decode the stream and then re-encode it) to generate a different version of the stream for each participant with different quality, resolution, and/or frame rate. Traditional solutions are based on the Multi-point Control Unit (MCU) model. One of the challenges of WebRTC multiparty solutions has always been how to adapt the video bitrate the for participants with different capabilities. Rainbow cake with white tea cup on the wood table In addition, frequent webrtcHacks guest author and renown video expert Gustavo Garcia Bernando joins him.īelow is a great piece that walks through a complex technology and yet-to-be documented features in Chrome’s WebRTC implementation. Sergio Garcia Murillo is a long time media server developer and founder of Medooze. Most recently, and most relevant for this post, he has been working on an open source SFU that leverages VP9 and SVC (the first open source project to do this that I am aware of). To help explain how it works we have brought in not one, but two WebRTC video architecture experts. Most would agree Scalable Video Coding (SVC) is the most advanced, but the most complex multi-party calling architecture. Note: If you uninstall and reinstall Canary, you need to run the above command again, to tell Google that you don’t want to get ASAN buids on Canary.Multi-party calling architectures are a common topic here at webrtcHacks, largely because group calling is widely needed but difficult to implement and understand. Reg add HKCU\Software\Google\Update\ClientState\\cohort /v hint /d asan-optout /f To opt-put of getting SyZyASan builds on Canary channel, you need to run following command in the command prompt with admin privileges. If you see Canary version number by selecting ‘About Google Chrome’ from menu it shows ‘canary SyzyASan’ under Google Chrome heading, what it saying is you’re using ‘SyzyASAN build’ like to Aura build. In the last three weeks, we’ve found 150 new bugs in Chromium, several of which could lead to security vulnerabilities.” “One day with a little slowdown on the Canary channel gives us plenty of great data. Though you’ll experience slowdown in performance of canary, Chromium team has advantages of running SyzyASAN instrumented build on Windows canary as it shows them hardest to locate memory bugs. ![]()
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