Skype Meeting Broadcast - recommendations when feeding video clips into Event?

Yeah, fantastic question.

So we generally use the same style of production in our high-end deliveries, I think with a difference of having a high-end board do all the mixing & normalization prior to it going down SDI or HDMI to ingestion by the SFB client.  There's a ton of different options here - from the setup you have to the Magewell we use to a dedicated capture card in a higher-end workstation. 

In every case they should be delivering 1920 video into SFB ingest and then we package and stream that up to Azure.  The client does have base encoding requirements for hardware and so I wonder if in some of your videos you're exceeding that.  Here's the article that goes through this technically https://technet.microsoft.com/en-us/library/jj688132.aspx - while not related to broadcast it does represent the client and media stack capabilities to encode the raw USB bitstream to H.264.

The only recommendation I have is to look into maybe front-ending everything by a board to normalize the input into the SDI->USB converter.