Reduce the size of an MP3 file
Have an MP3 that's too big to send by email, a voice recording, or a podcast to slim down? Pick a lower bitrate and switch to mono for voice: the file can lose 50 to 75% of its size without hurting speech.
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The bitrate determines the size: 128 kbps is about 1 MB per minute.
How to use it
- Install ffmpeg if you haven't already.
- Open a terminal in the folder containing your file.
- Copy the generated command, adjust the file names if needed, then run it.
- Open the resulting file to check the result.
Expected size by bitrate
At 128 kbps, one minute of audio weighs about 1 MB; 64 kbps comes to 0.5 MB; 32 kbps, 0.25 MB. An hour-long mono podcast at 64 kbps therefore stays under 30 MB.
Mono for voice
Voice recordings are almost always identical on both channels. Converting to mono cuts the amount of data in half with no real loss of quality. For music, keep stereo.
Frequently asked questions
Why is my file bigger after conversion?
If the original file has a lower bitrate than the one you chose, re-encoding makes it bigger without improving the sound. Always choose a bitrate lower than the source's. To find out what it is, use the file information page.
What bitrate should I use for a podcast or voice?
In mono, 64 kbps gives a very clear voice; 32 kbps is still intelligible for a lecture. For music, don't go below 128 kbps.
Does re-encoding degrade the sound?
Yes, a little: a re-encoded MP3 goes through a second round of lossy compression. Always start from the best source available if you still have it.
What does -map_metadata 0 do?
It copies the title, artist and album from the source file into the new file.