How to Extract MP3 Audio from an MP4 Video

You have a video file, but you only need the audio. Maybe it's a lecture recording your professor posted as an MP4, a music video you want to listen to on your commute, or a podcast someone published to YouTube. Whatever the case, you don't need the video track, and this guide shows you how to pull the audio out.

When You'd Need This

Students run into this constantly. A professor uploads a two-hour lecture as an MP4 to the course portal, and you want to listen while you're walking between classes or doing dishes. Converting it to MP3 lets you drop it into any audio player without dragging a video file around.

Podcast listeners face the same problem when a show publishes video-first. A lot of interview-style podcasts go to YouTube before (or instead of) RSS, which means the only copy you can get is a video file. Stripping the audio gives you something that works in a standard podcast app or music library.

Content creators use audio extraction for a different reason: repurposing. If you recorded a video tutorial and want to publish the audio as a standalone episode, you're starting with an MP4. Same if you're pulling your own guitar track from a video jam session to mix later.

How to Do It

1. Open the MP4 to MP3 converter in your browser.
2. Drop your MP4 file into the upload zone, or click to select it from your device.
3. Choose a bitrate. 128kbps works fine for speech; 192kbps or higher is worth it for music.
4. Click Convert and download the MP3 when it's ready.

The whole process runs in your browser. Nothing gets sent to a server.

What's Actually Happening

MP4 is a container format, not a codec. Think of it as a box that holds separate video and audio streams, each compressed with their own codec. Most MP4 files carry audio encoded as AAC (Advanced Audio Coding), which is efficient and high quality. The MP4 wrapper just keeps the audio and video streams synchronized.

MP3 uses a different codec (MPEG-1 Audio Layer III, encoded by LAME in this case). So when you "extract" audio from an MP4, you're not just pulling out a file that was already there in MP3 form. The tool has to decode the AAC audio stream and re-encode it as MP3. That re-encoding step is why bitrate selection matters, and why there's a brief processing time.

The re-encoding is done entirely by FFmpeg compiled to WebAssembly, running inside your browser tab. FFmpeg is the same open-source tool used by professional video editors, broadcasters, and streaming platforms. WASM just means it runs locally without needing a server.

Bitrate Comparison

Bitrate	File size per minute	Quality	Best for
128kbps	~1.0 MB/min	Good for speech; noticeable compression on music	Lectures, voice memos, podcasts
192kbps	~1.4 MB/min	Solid all-around	General music listening, podcast audio
256kbps	~1.9 MB/min	High quality; headphone-audible improvement over 192	Music you care about, archiving
320kbps	~2.4 MB/min	Ceiling of MP3 quality; transparent on virtually all content	Audiophile listening, production use

A Note on Privacy

Your files stay in your browser the entire time. No audio is uploaded, no copy is kept on a server, and there's no account required. That matters especially here: lecture recordings often contain private academic discussions, and personal videos may include conversations you wouldn't want stored on someone else's infrastructure. None of that leaves your device.