Bandwidth Estimation (BWE) for subscribers (WIP) #3278
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- parse recv delta as signed int from feedbacks - detect first recv delta in a chunk - fix cleanup of pkt queues - evaluate average delay in a time window of 1 second
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@lminiero Extremely useful. Thanks ! Reading through the blog post and the code, i have a couple of questions if you don't mind :
Thanks for your time. I apologize if these questions have obvious answers in the code. I tried reading the code but my C knowledge is very limited 🙏. |
No, not yet, and I won't integrate it in other plugins until I get enough feedback to consider the work close to done. If you're interested in getting this added to the Streaming plugin, please test the existing integration and provide feedback we can use.
Plugins will have a way to enable/disable this dynamically. In the current version of the code, for testing purposes the VideoRoom plugin always enables it for subscriptions. Again, once we're close to being done, I'll add APIs or configuration tweaks to make it configurable, but that's not what I'm interested in right now. I need to know if and how it works when enabled.
Plugins will have a way to set probing targets but there's no API for that yet, and I'm not sure there will be. At the moment the VideoRoom plugin automatically sets a target for the next simulcast layer you're interested in.
The Admin API has the current estimate, while we don't push this event to participants or event handlers yet. |
This is a first experimental draft of my BWE efforts on Janus: although it already "works", it's not in a finished state, since it needs a lot of tweaking and additions. I'm sharing this as a PR mostly to give a pointer to those who've seen (or will see, as I'm writing it hasn't happened yet!) my RTC.ON presentation on the subject.
Slides: https://www.slideshare.net/LorenzoMiniero/bwe-in-janus
Video: https://www.youtube.com/live/n6igQ2J3s80?si=mpvXUcCY0FeCjkp1&t=9804
Rather than implementing any of the existing algorithms (e.g., GCC), I followed the same approach @murillo128 followed for Medooze, meaning I decided to come up with a "homemade" approach myself starting from the fundamental concepts needed for the purpose. I actually need to thank Sergio a lot for that, not only because his effort convinced me it would be a good idea (when you know how things wotk, you can tweak more easily, which is definitely useful!), but also because navigating his code helped me a lot not getting lost in some of those BWE seas. There's other people I need to thank too (especially at the beginning, where I exchanged ideas about how BWE works at its core), but they know who they are!
In a nutshell, this PR creates a new concent, a BWE context that can be added to a PeerConnection in Janus. When created, Janus will try and estimate the available outgoing bandwidth for that handle using TWCC, monitoring the acked rate, losses, delays, determining probing, etc. When an estimate is available, the related plugin will be notified about it, so that it can decide what to do (e.g., switch simulcast layer for that subscriber). Using the Admin API, stats on the BWE context can be saved to a CSV file, and/or sent in real-time via UDP to an external application, where it can be graphed (I created a separate tool for that, that I'll probably share later on for those interested in using it for testing). If you want to learn more, you can check my presentation: I'll probably also write a blog post on all that in a few weeks.
As anticipated, this is not 100% done and is still quite experimental, but all the basics are all there: at the moment, I've partially integrated this in the VideoRoom, where you can test this working with a simulcast subscriber (as long as there's a single video in the PeerConnection). Next steps will be fine tuning this scenario as much as possible, until we're happy with it, which basically means testing it as much as possible in different conditions. Once that's done, it will be a matter of making the plugin integration "smarter" too, e.g., extending the VideoRoom support to multiple subscriptions in the same PeerConnection, SVC besides simulcast, etc.
If this is something that interests you (and it should!), please do take the time to test this! But again, please remember this is experimental: I'm not interested in generic feedback that just says "it works", "it doesn't work", etc. I need feedback I can actually use to improve things, which means providing more info, so please only contribute something if you're serious about testing this new stuff properly.