Important: the studio is responsible for audio and video throughout the entire broadcast of the talk!
Here's what viewers of one of the main channels will see:
The length of the slot in the schedule Fahrplan (40 or 60 minutes) is inclusive of all of the above.
If the talk has been pre-recorded, the speakers do not need to join quite as early. But the stuiod still needs to make sure the speakers are all available in time for the Q&A.