MP4 to MP3 Converter

Pull the soundtrack out of an MP4 — a lecture, a concert clip, a voice memo saved as video — and save it as an MP3 that plays on any phone, car stereo or music app. Conversion happens inside your browser, so the video is never uploaded. Most MP4 files are decoded by the browser itself and finish in seconds; anything the browser cannot read is handed to the built-in video engine (ffmpeg, a one-time download of about 30 MB).

How to use this tool

1. Choose one or more MP4 files (M4V, MOV and M4A work too).
2. Pick the MP3 quality: 192 kbps suits most music, 128 kbps is enough for speech.
3. Optionally enter a start and end time to keep only part of the audio, or switch to mono.
4. Press Calculate, then play the result or download it (several files can be downloaded as one ZIP).

Formula

MP3 size ≈ bitrate (kbps) × 1000 ÷ 8 × length (seconds)

Constant bitrate means every second takes the same space. VBR lets LAME use more bits on complex passages and fewer on quiet ones, at a similar average size. The audio is decoded to PCM and re-encoded with the LAME MP3 encoder. MP4, MOV and M4A files keep their sample rate when it is 32, 44.1 or 48 kHz; other files the browser decodes itself are saved at 44.1 kHz, and files that go through the video engine keep their own rate.

Example

A 4-minute MP4 music video converted at 192 kbps gives 192,000 ÷ 8 × 240 = 5,760,000 bytes, about 5.5 MB of MP3. The same audio at 128 kbps would be about 3.7 MB, and in mono at 128 kbps it keeps the same quality per channel for speech.