Touch Arcade:

Tunity allows you to hear any TV, whether its muted or not, anywhere, just by letting the app scan the screen for a few seconds. Tunity feels like magic- Particularly when paired with AirPods, and you seriously just have to try it.

You open up the Tunity app, let it scan the TV you want to hear sound from, and if it’s a supported channel (most over the air and standard cable channels seem to be supported) the audio will just start playing on your phone. If it’s out of sync at all, you can fine tune the delay to make the audio 100% match up with the picture. It is borderline ridiculous how well this works.

I’ve used Tunity for years with varying levels of success. When it works, it’s really cool.