This feature is on the teams backlog. Thank you for your votes and comments.
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Please add preview support in Teams for IRM protected files.
Share video and audio during meetings is released on Windows. Mac support is now planned for CY20Q3.
Note: Live events support for video and audio is tracked in this item – https://microsoftteams.uservoice.com/forums/555103-public/suggestions/38470144.
Please refer to this page for more info on this feature: https://support.office.com/article/share-system-audio-in-a-teams-meeting-dddede9f-e3d0-4330-873a-fa061a0d8e3b.