Converting an MP4 video file to MP3 extracts the audio stream from the container and saves it as a standalone audio file, discarding the video track entirely. MP4 is a multimedia container that can hold video (H.264, H.265), audio (AAC, MP3), and subtitle streams simultaneously. MP3 is a dedicated audio format using the MPEG-1 Audio Layer III lossy compression algorithm, widely supported across all devices and media players. During extraction, the existing audio codec is either copied directly (stream copy) when it is already MP3, or re-encoded from AAC to MP3 using the LAME encoder at the selected bitrate. Common output bitrates are 128 kbps (voice or podcast quality), 192 kbps (standard music), and 320 kbps (near-lossless music). 1converter uses FFmpeg for this conversion, which ensures accurate audio sync, correct sample rate handling, and ID3v2 metadata preservation where present in the source file.