I'm trying to build a little led show with an Arduino. The idea is that I time and plan changes in the lightning for a specific video and later play it on a screen in sync with the show I previously programmed on the Arduino.
I've managed to achieve the result with a photoresistor taped in a corner of the screen. By flashing the pixels underneath it black-white-black at the beginning of the video the Arduino knows when to start the pre-programmed sequence and plays the show in sync with the video/audio.
Even though the solution works I'd prefer to have something less visible, so I thought of adding at the start of the audio track a high-pitched noise. My speakers can't play that sound but it could be detected by the Arduino if somehow I feed it a copy of the audio signal. The problem is that I have no idea how to approach something like that.
Maybe there's something simpler I could do.