You can use NewTek NDI® (Network Device Interface) protocol to connect Microsoft Teams to the Webcast solution via local intranet.
Specifically, your Webcast stream can be directly broadcast to Microsoft Teams in real-time, significantly improving your event experience.
Prerequisites
Ask your administrator to enable NDI access using the Microsoft Teams admin center.
Specifically, NDI®-out needs to be turned on for each individual user. For more information, consult this article.
Steps
Once the admin has enabled NDI, the end user must turn on NDI® technology in the Microsoft Teams client from Settings > Permissions:
Then, the end user should navigate to the meeting controls and select More actions 
and choose Broadcast over NDI:
Whenever the end user joins a meeting, they will be notified that the meeting is being broadcast by a banner message:
Note that if they do not want to be part of the broadcast, they will have to leave the meeting.
Use with video mixing software
In a video mixing software, you can choose the NDI source from the Network section.
In OBS, for example, you can select the NDI source under Tools > NDI Output Settings:
