Free tool
Compress MP3 files online, free and private
Compress an MP3 by re-encoding it at a lower bitrate, and see the size before and after.
Your MP3
Drag a file here, paste it, or choose one.
.mp3, .wav, .m4a, .aac, .ogg, .oga, .opus, .flac, .aif, .aiff. Up to 500 MB.
Up to 3 hours of audio.
Your file never leaves your browser. The conversion runs on this machine.
More options
Trim
Leave both empty to keep the whole file. Seconds like 1:05.5 work too.
Result
Worked example
Measured on our own 2 minute 17 second narration as a 320 kbps MP3, compressed to 64 kbps mono.
Source, 320 kbps
5.2 MB
64 kbps mono
1.0 MB
80% smaller. One voice loses nothing it needs in mono, and 64 kbps on a single channel is still clear speech.
1. Add your file. 2. Pick the output. 3. Convert in the tab. 4. Listen and download.
What Interlace does
Short, clear narration from the start.
- Pick the video length before it is made
- The script and the voice are written to fit
- Download an MP4 at the size your LMS wants
Real Interlace output, unedited. Shown silent and sped up.
Your file
episode-41.mp3
320 kbps to 64 kbps mono
Questions
Asked and answered
No. The file is read by the page and converted by ffmpeg compiled to WebAssembly, on your own machine. There is no upload step, and closing the tab discards everything.
Size is bitrate times length. At 64 kbps an hour is about 27 MB, at 48 kbps about 21 MB. Mono at the same bitrate is the same size as stereo but sounds clearer for speech.
Yes, a lower bitrate always removes some detail. For speech, 64 kbps mono is hard to tell from the original. For music, 128 kbps is about as low as most people are happy with.
Because its bitrate was already at or below the one you picked. The tool shows the source bitrate when you add the file and warns you before you convert. Re-encoding at a higher bitrate only makes a bigger file of the same quality.
For a podcast, a lecture or a voice note, yes. Mono spends the whole bitrate on one channel, so 64 kbps mono sounds close to 128 kbps stereo. Music with a wide stereo image will sound narrower.
Turn this into a video
Create an account and start from a document, script, or prompt.