MP4 to MP3 Converter

What's actually happening when you "extract" audio

An MP4 file is a container: video stream, audio stream, and sometimes subtitles or chapter data, all multiplexed together. The audio inside is usually AAC, occasionally MP3 or Opus. To get a standalone MP3 file, this tool runs ffmpeg.wasm — a WebAssembly build of FFmpeg — right in your browser tab. FFmpeg demuxes the container, pulls out the audio track, decodes it to raw PCM, and re‑encodes it to MP3 at the bitrate you pick. All of that happens locally; nothing is uploaded.

Because WebAssembly doesn't have the same access to your CPU as native FFmpeg, processing is slower than the desktop version — expect roughly real‑time for a typical file (a 5‑minute video takes a few minutes on a laptop). The first load also pulls down around 25 MB of WASM, so the initial page can feel slow; subsequent conversions are much faster because it's cached.

Choosing a bitrate

• 128 kbps — speech, podcasts, audiobooks. Indistinguishable from the source for voice content, half the size of 320.
• 192 kbps — the default. Good for most music; generally considered transparent for casual listening on earbuds or phone speakers.
• 256 kbps — music you'll listen to often on good headphones.
• 320 kbps — the MP3 maximum. No reason to pick higher unless you're archiving, and even then FLAC would be a better choice.

One thing worth knowing: if the source video's audio is already at (say) 128 kbps AAC, re‑encoding to 320 kbps MP3 doesn't add any quality — you can't un‑lose detail that was already thrown away. It just makes the file bigger. Match or go slightly below the source bitrate.

Common uses

• Turning a recorded Zoom call (.mp4) into a podcast episode or voice memo.
• Saving the audio from a lecture recording to listen to on a commute.
• Pulling the audio from a phone video you shot yourself — useful for interviews.
• Creating a ringtone from a clip you own.

Please don't use this to strip audio from videos you don't have the rights to — that includes YouTube and streaming service content, which have their own terms of use.

Limits

Because everything runs in your browser's memory, very large files (over a few hundred MB) may cause the tab to run out of memory. For anything that long, installing real FFmpeg on your machine is the right move — ffmpeg -i input.mp4 -vn -b:a 192k output.mp3 is the equivalent command. This tool supports MP4, MOV, AVI, WebM, and MKV as inputs; any of them that contain a decodable audio track will work.