How to use it
- Drop the MP3 file. Its sample rate is read from the frame header so it is decoded without resampling.
- Select the part to keep and press Trim, or the part to remove and press Delete.
- In Export choose MP3 and a bitrate: 128 kbps for speech, 192–320 kbps for music.
- Type a title and artist if you want them embedded as ID3 tags.
- Press Export, wait for the verification badge, then Download.
Why the MP3 is re-encoded
An MP3 is made of frames of 1,152 samples, and each frame depends on the previous one. Cutting exactly at an arbitrary millisecond means decoding and encoding again. MusicCutter decodes your MP3, applies the edit at sample precision, and encodes a fresh constant-bitrate MP3 using lamejs, a JavaScript port of the LAME encoder, inside a worker on your device.
To keep generational loss small, export at the same or a higher bitrate than the source. If you plan to edit again later, export WAV now and encode MP3 once at the end.
Checking the result
After encoding, the new file is decoded again in your browser and its duration compared with the selection. The badge reports the measured length and any difference, which for MP3 is the encoder padding of roughly 25–50 ms, because no gapless header is written.
Questions
Which MP3 bitrate should I choose?
128 kbps is fine for voice and casual listening. 192 kbps is a good default for music; 320 kbps is the maximum MP3 supports.
Can I keep the original MP3 frames without re-encoding?
Not in this version. Frame-copy cutting is lossless but only cuts on 26 ms frame boundaries; it is on the roadmap. Today every MP3 export is re-encoded.
Are ID3 tags from my original file kept?
No, the original tags are not copied. You can type a new title and artist, and add cover art, in the Export panel.