How to convert MP4 to MP3
- Choose one or more videos (or add more later).
- Pick MP3 and a bitrate (or WAV for lossless sound), and tick Convert only part of the video if you need a section.
- Press Convert to MP3, listen to each result and download it.
How it works
The video's sound track is decoded by your browser, the same way the Video to audio tool does it, then encoded to MP3 with LAME, the open-source MP3 encoder. Stereo and mono are kept; surround sound is mixed down to stereo. Videos over 45 minutes or 300 MB are read a piece at a time with the browser's WebCodecs audio decoder, so even a 2 GB video converts without running out of memory.
Example
A 4-minute video at 192 kbps: 192,000 ÷ 8 = 24,000 bytes a second, × 240 seconds = 5,760,000 bytes, which the tool shows as 5.49 MB. The same 4 minutes at 128 kbps is 3.66 MB, and at 320 kbps 9.16 MB.
Only convert videos you own or have permission to use. Ripping copyrighted music or films can break the law and platform terms.
MP3 files are encoded with LAME (lamejs 1.2.1, licensed under the LGPL-3.0), which is loaded unmodified as a separate file. Licence and source code.
Video files are read and written with Mediabunny 1.61.3 (Mozilla Public License 2.0), loaded unmodified as a separate file, and coded by your browser's own video and audio encoders (WebCodecs). Mediabunny reads the video files and, for long videos, hands the sound over a piece at a time. Licence and source code.