MP3 Encoder
Convert WAV, OGG, M4A, FLAC, or other audio files to a real, compressed MP3 — encoded entirely in your browser using a JavaScript port of the LAME encoder. Files up to 50 MB are never uploaded to a server.
Click to upload or drag and drop
WAV, OGG, M4A, FLAC, or other common audio formats
How this differs from the Audio Converter
The site's Audio Converter can only output uncompressed WAV, since your browser can decode compressed audio but can't re-encode it without a dedicated encoder library. This tool adds that missing piece specifically for MP3 — the most widely compatible compressed format — using a JavaScript port of LAME, the same encoder most desktop MP3-encoding software is built on.
Choosing a bitrate
128 kbps is a reasonable minimum for spoken word or casual listening; 192 kbps is a solid, broadly recommended balance for music; 320 kbps is the highest standard MP3 bitrate and close to indistinguishable from the source for most listeners, at the cost of a larger file. Changing the bitrate re-encodes the same decoded audio instantly, without needing to re-upload the file.
How big will the MP3 be?
The encoder holds a constant bitrate, so the size depends on length and the bitrate you choose, not on how complex the audio is. The rule is kilobits per second ÷ 8 × seconds, in thousands of bytes. One minute is about 960,000 bytes at 128 kbps, 1,440,000 at 192 kbps and 2,400,000 at 320 kbps. A three-minute track at 192 kbps comes to about 4.3 million bytes, which the tool shows as 4 MB. Mono and stereo give the same size at the same bitrate, because the bitrate is the total for the file.
What is encoded
- A mono file stays mono. Anything with more than two channels is encoded using only the first two (left and right), so surround tracks lose their other channels.
- The sample rate of the decoded audio is kept, and the samples are converted to 16-bit before encoding.
- No title, artist or cover art is written, so the MP3 has no tags. The output is named after your file with .mp3 on the end.
- Encoding runs on the page itself rather than in a background worker, so the tab can stop responding for a moment on a long recording.
What it accepts
The file must be reported by your browser as audio, and up to 50 MB. Your browser's own decoder opens it first, so a format the browser cannot play, or a damaged file, shows "Couldn't decode that audio file". Changing the bitrate afterwards re-encodes the audio already held in memory.
Frequently asked questions
How is this different from the Audio Converter tool?
The Audio Converter can only output uncompressed WAV, since browsers don't include a built-in MP3 encoder. This tool adds a dedicated JavaScript MP3 encoder (a port of LAME) specifically to produce real, compressed MP3 output.
Is the quality as good as a desktop MP3 encoder?
Yes — this uses a JavaScript port of LAME, the same encoder most desktop MP3 software is built on, not a simplified or lower-quality substitute.
Why does re-encoding an existing MP3 lose quality?
MP3 is a lossy format — some audio detail is permanently discarded during encoding to shrink the file. Decoding an MP3 and re-encoding it (for example, to change the bitrate) compounds that loss a second time, known as generation loss. For the best result, encode from the original uncompressed or lossless source when you have it.
How large will a 5-minute song be at 320 kbps?
About 12 million bytes (320 ÷ 8 × 300 = 12,000 kilobytes), shown by the tool as 11 MB. At 128 kbps the same song is about 4.8 million bytes.
Does the MP3 keep the song title and artist?
No. The encoder writes only audio, with no ID3 tag, so the title, artist and artwork must be added in a tag editor afterwards.
What happens to a 5.1 surround file?
Only the first two channels are used, so the result is a stereo MP3 made from those two. The centre, rear and bass channels are not mixed in.