What does MP4 to MP3 Converter do?
Convert MP4 to MP3 in your browser: extract audio from MP4, MOV, WebM, MKV or AVI at 128 to 320 kbps or VBR, with optional trimming. No uploads.
- Price
- Free
- Account
- Not required
- Processing
- Entirely in your browser; your data and files are not uploaded
- Works on
- Any modern browser on desktop, tablet or phone
- Category
- Video and Audio Tools
How to use the mp4 to mp3 converter
- Drop a video file (MP4, MOV, WebM, MKV or AVI, up to 300 MB) or click to choose one.
- Pick constant bitrate (128, 192, 256 or 320 kbps) or a LAME VBR quality level.
- Optionally turn on trimming and enter a start and end time to convert only part of the video.
- Click Convert to MP3, wait for the progress bar, then play the preview and download the MP3.
Worked example
A 6 second clip at 192 kbps
At a constant 192 kbps, audio uses 192,000 bits per second, so 6 seconds is 192,000 x 6 / 8 = 144,000 bytes, about 141 KB. Testing the tool with a 6 second MP4 produced a 143 KB MP3 (the extra is MP3 frame padding and the encoder delay).
How it works
The video is mounted read-only into FFmpeg's virtual file system and FFmpeg runs -i input -map 0:a:0 -vn -c:a libmp3lame -b:a 192k output.mp3 (or -q:a for VBR). Only the first audio track is decoded and re-encoded with the LAME MP3 encoder; the video stream is ignored. Trimming seeks with -ss before the input and limits the length with -t.
Assumptions
- The video must contain an audio track. Silent videos cannot be converted.
- MP3 encoding is lossy. If the source audio is AAC at 128 kbps, a 320 kbps MP3 is larger but not better.
- Only the first audio track is used when a file has several (for example, multiple languages).
Frequently asked questions
Are my files uploaded?
No. The file is processed by FFmpeg compiled to WebAssembly, running inside your browser. Only the engine itself is downloaded (once, from cdn.jsdelivr.net); your video, audio or images never leave your device.
Which bitrate should I choose?
192 kbps is a sensible default for music and more than enough for speech. 320 kbps is the MP3 maximum. VBR (variable bitrate) spends more bits on complex passages and fewer on quiet ones, often giving a smaller file at similar quality.
Can I convert only part of a video?
Yes. Turn on "Only convert part of the video" and enter start and end times such as 1:05 or 0:30.5. Leave the end empty to go to the end of the video.
Why does the first run take longer?
The first time you use any of the video and audio tools, your browser downloads the FFmpeg engine, about 31 MB. It is stored in your browser, so later runs on this device start without downloading it again unless you clear site data.
Limitations
- FFmpeg runs as single-threaded WebAssembly in the browser, which is much slower than desktop FFmpeg. Processing time depends on the file length, resolution and your device; long HD videos can take many minutes.
- Browsers limit how much memory a page can use. Very long or high resolution files can fail with an out of memory message, especially on phones and tablets.
- Files up to 300 MB are accepted.
- Copy-protected (DRM) videos cannot be read.