This guide explains how to convert MP4 video files to MP3 audio using the open-source tool FFmpeg. It covers basic command-line usage for extracting audio with the LAME MP3 encoder, options for adjusting audio quality through variable or constant bitrate settings, and advanced features such as stereo/mono conversion, custom sample rates, and metadata preservation. Best practices are included for testing and compatibility to ensure efficient, high-quality audio extraction. FFmpeg offers a robust, cross-platform solution ideal for developers and media processors needing reliable audio conversion from video.