How to Record Audio from Incoming Calls with Node.js

This tutorial extends a voice application created in a previous tutorial, allowing it to record a message from a caller using the Nexmo Voice API and the Node.js client library. To complete this tutorial, developers need to set up a Vonage API account and create a virtual phone number. They then modify the NCCO to handle requests for recording audio, including specifying an event URL where information about the recording is sent. When a recording is completed, the event returns the information, including the audio file URL, which can be used to retrieve the recording from Nexmo. Developers also learn how to download the recorded audio file to their disk using the `files.save` method of the Nexmo Node.js library.