I would like to be able to listen to music through headphones while the wife watches a video stream via HDMI, on the same laptop. By default this is impossible, since plugging in the HDMI cables sends ALL audio to the TV. Is there an easy way to split the computer's audio between HDMI and headphones by application?
I'll assume you're using Windows for this answer.
Yes, but it depends on the program you're using. The program must support choosing the audio device it outputs to. If it does, it's as simple as finding and changing that setting.
Windows Media Player, VLC Media Player, Winamp, and Foobar2000 support this. I don't believe iTunes or Groove Music do, however. Also, I'm not aware of any web browser that supports it, so any streaming services that work through the browser won't either. The Pandora and Spotify native apps don't support it.
P.S. You can find a listing of your computer's audio devices by right-clicking the volume icon in the taskbar and selecting "Playback devices." Note that some might be hidden. Right-click in the window and select "Show Disabled Devices" and "Show Disconnected Devices" to reveal them.