StarTech.com IPUSB2HDMI Instruction Manual page 17

Media Playback
Please note that while operating in Extended Mode, the USB Display
Adapter can display media files and DVDs using a broad variety of
media players, however in Clone Mode, limited support is available for
video playback.
Audio Playback
The audio component of the HDMI Video Adapter adds a new USB
sound device to the system. This will be selected by default, but on
some system it may need to be selected manually through the Sound
Preferences in System Preferences. Audio will only be passed through
the converter to the HDMI display. Any speakers connected directly to
the computer system will not be active, while audio is being sent to the
HDMI Video Adapter. If multiple HDMI Video Adapters are connected
to the computer system, only one audio device can be used. So audio
can only be output to one of the HDMI Video Adapters.
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