MP3 Cutter & Audio Trimmer
Cut any audio file on its waveform — frame-accurate and lossless for MP3 and AAC.
Details from the file
Select the part
Drag the handles or the waveform; click to place the playhead. Keys: Space plays, I and O set the start and end at the playhead, + and − zoom. A focused handle moves with the arrow keys (10 ms; Shift 1 s; Alt one frame).
Save as
What you will get
Output
Working…
Your cut
Change the settings above and run it again to try another version; the original stays open.
About the MP3 Cutter & Audio Trimmer
Cut any audio file on its waveform: drag the handles (or type the times) to select a part, then keep it or delete it and keep the rest. Zoom in to place a cut precisely, loop the selection while you listen, and add a fade in or fade out.
For plain MP3 and AAC (M4A) files the cut is saved without re-encoding: the original audio frames are copied, so the quality is untouched and saving takes a moment. A lossless cut lands on the nearest audio frame boundary — at the usual 44.1 and 48 kHz, frames are 21–26 ms long, so within about 13 ms of where you put it — and the page shows exactly where. WAV and FLAC are cut to the exact sample, losslessly. With fades, or when you want another format, the result is encoded as MP3, M4A or WAV.
Everything happens in your browser; nothing is uploaded.
How to use it
- Drop an audio file on the box or press Choose an audio file. The waveform appears while the file is read.
- Drag the two handles (or the selection itself), or type the Start and End times. Zoom in with the + button, Ctrl/⌘ + scroll or a two-finger pinch for precise cuts.
- Choose whether the selection is kept or deleted, add fades if you like, and press Play selection (with Loop) to check it.
- Under Save as, keep the same format (no re-encoding) or pick MP3, M4A or WAV, press Cut audio and Download.
Examples
talk.mp3 · 128 kbps · select 0:03.2 to 41:10.0 · Kept · Same format
talk-cut.mp3 · the same frames copied, cut at the nearest frames (0:03.213 and 41:09.997)
song.m4a · select 1:02.0 to 1:31.5 · fade in 1 s · fade out 2 s · M4A 192 kbps
song-cut.m4a · 29.5 seconds; rename it to .m4r to add it to an iPhone (ringtones must be 40 seconds or shorter)
podcast.mp3 · select 12:40.0 to 14:05.5 · Deleted · MP3 V2
podcast-cut.mp3 · 1 min 25.5 s shorter, with a 10 ms crossfade so the join does not click
Why MP3 and AAC can be cut without re-encoding
MP3 and AAC store sound in small frames: 1,152 samples per MPEG-1 Layer III frame (ISO/IEC 11172-3), 26.1 ms at 44.1 kHz and 24 ms at 48 kHz, and 1,024 samples per AAC frame, 23.2 ms at 44.1 kHz. A cut on a frame boundary can copy the frames as they are, so there is no second generation of compression and no change in quality. That is also why a lossless cut moves to the nearest boundary; zoom in and the page draws the frame grid.
For AAC in M4A the frame just before the cut is kept as decoder priming and hidden with an edit list, so the cut starts cleanly. MP3 frames can borrow bits from the frames before them (the “bit reservoir”), so the very first frame after a cut may be silent for a moment (at most one frame). If you need sample-exact cuts or fades, choose a re-encoded format.
Keeping or deleting, fades and joins
Kept (cut it out) saves only the selection. Deleted (keep the rest) removes the selection and joins what is before and after it; when the result is re-encoded the join gets a 10 ms equal-power crossfade so it cannot click, and Play the join lets you hear it before saving. Fades are linear: the fade in starts the result from silence, the fade out ends it in silence, and Play selection plays them as they will sound.
Re-encoding uses LAME for MP3 (constant bitrate or VBR), the browser’s AAC encoder (or a WebAssembly one) for M4A, and plain PCM for WAV. Same-format WAV and FLAC cuts write the kept samples unchanged.
Limitations
- Lossless MP3/AAC cuts move to the nearest audio frame (within about 13 ms at 44.1 or 48 kHz) and cannot have fades.
- One selection at a time: to remove several parts, cut, then open the result and cut again.
- Opus, Vorbis, AC-3 and other formats are re-encoded when cut; formats browsers cannot decode (WMA, AMR, ALAC outside Safari) cannot be opened.
- If the browser cannot play a format itself (AIFF in Chrome, for example), preview playback uses decoded audio kept in memory, which is skipped for very long files.
- Very long files take a while to draw on phones; you can already select by time while the waveform is read.
Privacy
Everything happens in your browser. What you enter or open here is not uploaded or stored by MySmartCoPilot. The audio engine (and, when you re-encode, the LAME MP3 or AAC encoder) downloads from MySmartCoPilot the first time you use it. Your audio is never uploaded.
Frequently asked questions
Does cutting an MP3 reduce its quality?
Not with Same format, no re-encoding: the original frames are copied unchanged. Only fades or a change of format re-encode the audio.
Why did my cut move by a few milliseconds?
A lossless MP3 or AAC cut has to land on a frame boundary. At 44.1 and 48 kHz frames are 21–26 ms long, so the page moves each cut to the nearest one (by about 13 ms at most) and shows the exact times. For a sample-exact cut, choose MP3, M4A or WAV under Save as.
How do I make a ringtone?
Select up to 40 seconds (the iPhone limit for ringtones), add a short fade out, and save as M4A for an iPhone — rename the file to .m4r and add it with Finder or iTunes — or as MP3 for Android.
Can I remove a part from the middle?
Yes. Select the part, choose Deleted (keep the rest), check the join with Play the join, and press Cut audio.
Can I control it with the keyboard?
Yes. Tab to a handle and move it with the arrow keys (10 ms; Shift for 1 s; Alt for one frame; Page Up/Down for 5 s). Space plays the selection, I and O set the start and end at the playhead, + and − zoom.
Is my audio uploaded?
No. The file is read, shown and cut in your browser; only the tool’s code is downloaded the first time.