how to use hdmi and headphone jack simultaneously

Select a Master Device in the drop-down menu.

(If one is a wired pair, tick Built-in Output.)

Tick the sets of headphones that you want to use in the Audio Device list.

(You can also opt to Play Alerts and Sound Effects Through This Device from the same menu.)

Right-click (or Ctrl-click) the Multi-Output Device in the list that you just created, and select Use This Device For Sound Output.

Click the plus ( +) button at the lower left of the Audio Devices window and select Create Multi-Output Device.

Launch the Audio MIDI Setup app, located in Applications/Utilities.

Make sure that the headphones you want to use together are paired with your Mac over Bluetooth and/or connected via the headphone jack.

How to Output Mac Audio to Two Audio Devices

two sets of AirPods), or even several pairs. The method described below should work regardless of whether you're using one wired pair and one wireless pair of headphones, two pairs of Bluetooth headphones (i.e. Next time you're on a flight with someone and you both want to watch a video on your Mac without disturbing other passengers, try this convenient solution for sharing your Mac's audio among two pairs of headphones.

How to use hdmi and headphone jack simultaneously