If you are playing a video for your students through Zoom, you will need to check an additional setting when you share your screen. This technique will also be important if you need to play a video for in-person and remote students at the same time.
Video Demonstration
Here is a 5 minute video demonstrating how to tell Zoom to share your audio along with your screen.
Share Computer Audio
Note: The first time you share computer audio, Zoom will need to install a new audio component. I recommend that you restart your laptop after this installation.
In your Zoom meeting click the Share Screen button and choose the desktop or window you want to share, just as you normally would. However, before you click the Share button, look in the bottom of the window for a checkbox labelled Share computer sound.
Check this box, then click the Share button.
The very first time you check the Share computer sound box, you will likely see a message like this:
Enter the user name and password which you use to sign in to your laptop. After this installation is done, I recommend that you restart your laptop to ensure that the feature works correctly. This will only happen the first time you check the box.
Play Audio Through Zoom & Your Classroom Display
If you need to play a video for in-person students using your classroom display and also play that same video through Zoom for remote students, you will need to do one additional step in Zoom.
In Zoom, click the arrow next to the Mute/Unmute button. In the Select a Speaker section, choose the name of your classroom display, connected over AirPlay.
This will ensure that the sound plays both through the classroom display and through Zoom for remote students.