Ask HN: What affects live stream video quality

I've been watching a lot of live streams in the last month. YouTube seems to have the best video quality and Facebook and StageIt the worst. But I watched a StageIt concert the other day and was inadvertently still connected to my company VPN and the video quality was quite good. Could Comcast be rate-limiting StageIt, but they can't tell I'm live streaming over a VPN? What else affects the quality? - Platform (Facebook, YouTube, etc.) - Upload Speed of the Performer - Download Speed of the Listener - VPN Usage - Wifi Quality of the Listener - Airplay Quality - other?