Problem: MacBook (or podium Mac Mini) connected via HDMI or USB-C video cable, have video but no audio
Solution: Set audio output device in System Preferences → Sound → Output, to the HDMI or DisplayPort device.
Typically named "Crestron" in Sound Preferences, some newer spaces may be named "Classroom System" or "Room Speakers".
This is extremely common with a new MacBook, or a MacBook connecting to a specific classroom for the first time.
Once set, it will typically remember the setting when connected to HDMI the next time
Problem: Audio crackles or drops out when connected to HDMI cable in classroom
Solution 1: Reboot MacBook (too many open apps/windows have caused this issue).
Solution 2: On 2022+ MacBooks in rooms with HDMI cables with tethered USB-C adapters: bypass the USB-C to HDMI adapter and plug the HDMI cable directly into the MacBook’s HDMI port on the right side. Verify audio settings in System Preferences → Sound.