Noise cancelling app

If I understand Motsame's question right, the app would listen to the surrounding noise through the microphone, calculate the necessary inverse sound waves to cancel that noise, and then play those inverse waves through the speaker or headphones, potentially simultaneously with the intended sound (e.g., music). The result being cancellation of the noise similar to active-noise-reduction headphones. There is a problem in that active noise cancellation typically must be done in a very limited space to make it both useful and affordable, but maybe could work with ear buds? I can't recall seeing an app like this.

There is no way anyone could write it, they would not have access to the required processes.

It would be easier to get noise cancelling headphones. And you couldn't do such an app.

What would you use this app for?

Yes I do understand and I understand noise-reducing headphones. I don't understand what your app would do.