As shown, that thing in the video has a high probability of destroying whatever audio device it's connected to...
The "transmitter", as shown, puts the battery voltage across and the LED current through the audio output circuit of whatever it is plugged in to.
To me, it appears to be a scam; if it works without causing damage it's more luck than design!
(And anything with an output cap is not going to pass any DC at all, unless it also destroys the cap by reverse bias..)