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MP4 to MP3 Converter

Free · No sign-up · Files never leave your device

How do you convert MP4 to MP3?

To convert MP4 to MP3, you take the sound track out of the video, decode it, and encode it again as an MP3 file at a bitrate such as 192 kbps. This converter does all of that in your browser. The browser's own decoder reads the sound, and lamejs, a JavaScript version of the LAME encoder, writes constant-bitrate MPEG-1 Audio Layer III at 128, 192 or 320 kbps.

How it works

  1. Step 1

    Your browser reads the sound

    The file opens in this tab and your browser's own decoder turns its sound track into audio. The picture is skipped. Nothing is uploaded.

  2. Step 2

    Pick MP3 or WAV

    Choose MP3 at 128, 192 or 320 kbps (192 is the default) or 16-bit WAV. The page shows the length, channels and sample rate, and the estimated file size.

  3. Step 3

    Convert and download

    A background worker encodes the sound a few seconds at a time, so the page stays responsive and Cancel works. The file keeps its name, with .mp3 at the end.

Questions

Is my video uploaded?

No. The video is opened, decoded and converted inside this browser tab, and the MP3 is saved from it. The only thing that downloads when you convert is the MP3 encoder's code, which comes from 12notez.com to your device.

Which files work?

Any video or audio file whose sound your browser can decode. In Chrome that includes MP4, MOV and M4V with AAC sound and WebM with Opus sound. If the video has no sound track, or your browser cannot decode its sound, the page says so and names a browser to try.

How long can the video be?

About 93 minutes in Chromium. The browser decodes the whole sound track into memory before it converts, and Chromium refuses very long ones. On a computer with 16 GB of memory, a 93-minute stereo 48 kHz video converted to MP3 and a 94-minute one did not. Other browsers and devices have their own limits. If a file is too long, the page says so.

Which bitrate should I pick?

192 kbps is the default. A higher bitrate keeps more detail and makes a larger file: one minute is about 960 KB at 128 kbps, 1.4 MB at 192 kbps and 2.4 MB at 320 kbps, the highest bitrate MP3 allows.

Does converting to MP3 lose quality?

Yes, a little. MP3 is a lossy format, and the sound in most videos is already lossy AAC or Opus, so it is compressed a second time. 320 kbps keeps the most. WAV keeps the decoded sound with no MP3 step, at about 11.5 MB a minute for 48 kHz stereo.

Privacy: what runs where

  • Your video is read, decoded and converted in this browser tab. It is never uploaded.
  • The MP3 encoder (lamejs) loads from 12notez.com when you start a conversion. Nothing about your file is stored on our servers.
  • Only convert videos you have the rights to. The sound from someone else's video is still their work.

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