FFmpeg is an open-source command-line tool capable of decoding, encoding, transcoding, muxing, demuxing, streaming, filtering, and playing a large variety of media formats. To use FFmpeg in a C# .NET application, you'll need to download and install the binary, set up your development environment, and add the FFMpegCore NuGet package to your project. The library provides a simple and readable way to interact with FFmpeg from .NET. You can convert audio files to different formats using the FromUrlInput and OutputToFile methods, or use pipes to pass in data and receive data back without network or file I/O. This tutorial covers the basics of working with FFmpeg in C# and provides examples for converting audio files between different formats.