I simply want to be able to programmatically change the audio of a video to use headphones and not hdmi. Is this possible?

Question

I tried

amixer cset numid=3 1

but I get

amixer: Cannot find the given element from control default

I tested the headphones with

speaker-test -t sine -f 440 -c 2 -s 1

and hear the sound through the headphones and not the tv so I know the hardware works.

But I want the mp4 video I'm playing to redirect the sound to headphones not tv