Questions about adaptive bitrate ingesting to twitch server

Insights
1

I don’t really know where to post this question, but I hope I could get any answers from the
developers.

As I know by doing some research,
popular CDN based live streaming platform(e.g, twitch.tv ) provides recommended encoder settings (resolution, bitrate, fps) for broadcasters who use advanced software encoder (e.g, obs, xsplit).
Before doing live stream, broadcaster should test one’s upload bandwidth and select one of the recommendations. And once the encoder setting is selected, it can’t be changed during live stream.

On the delivery side however, there is popular adaptive bitrate streaming (DASH, HLS) to cope with heterogeneous bandwidth state of the viewers.

[CDN based live streaming architecture]

<--------------Ingest Side------------------->    <------Delivery Side--->          
                    RTMP                                 HLS
[Broadcaster] ----------------> [Media Server]--->[CDN]--------> viewer 1
              constant bitrate                           | 720p
                                                   ABR   |-----> viewer 2
                                                         | 360p
                                                         |-----> viewer 3
                                                           240p

My question is,
why live streaming platform, like twitch, does not provide any bitrate adaptation during ingest to media server?
Or do they have bitrate control only on their mobile apps?
In my opinion, adaptviely changing bitrate according to publisher’s bandwidth seems necessary and reasonable in case of bad network or bandwidth fluctuations.

Is there any bitrate adaptation for live ingesting side that I don’t know of?
I know that realtime video systems(e.g, webRTC, Hangouts) has their control logic to deal with congestion and packet loss.
Therefore, I assume that mobile streaming apps for youtube live, twitch.tv have their own bitrate control logic as well.
However, I couldn’t find any docs or information about it and also couldn’t find any, for the case where broadcasters use advanced encoder to do better live streaming.

2

All I can do is link you to the help guides

https://help.twitch.tv/s/article/broadcast-requirements?language=en_US
https://help.twitch.tv/s/article/guide-to-broadcast-health-and-using-twitch-inspector?language=en_US

Twitch clearly has a reason for running CBR on computers, and adaptive bit rate just has to be done on mobile due to the spotty nature of cellnet data coverage.

But this isn’t really a question for this forum, as

  • this sub forum is for discussion and support of analytics related to extensions and mods provided via curse forge/twitch app
  • this forum is for support of the various TwitchAPI’s (non streaming) for third party developers.

I wouldn’t call OBS/XSplit “advanced” myself.

You are in the wrong place for such a question and are unlikely to get an answer from Twitch about why they do it a particular way since it pertains to how the transcoders are configured.