Skype for Business, Simultaneous Skype for Business video streams
Only 5 video streams are visible at any one time.
How many video streams can I see in Skype for Business meetings?
In video conferences that have more than two people, users can see videos of participants in the conference. If the conference has more than five participants, video of only the most active participants appears in the top row, and a picture appears for the other participants.
More information can be found here: