ffmpeg being inprecise when trimming mp3 files

Question

I want to use ffmpeg to trim some mp3s without re-encoding. The command I used was
ffmpeg -i "inputfile.mp3" -t 00:00:12.414 -c copy out.mp3
However, out.mp3 has a length of 12.460s, and when I load the file in Audacity I can see that it was cut at the wrong spot, and not at 12.414s.

Why is this? I googled a bit and tried some other commands like ffmpeg -i "inputfile.mp3" -ss 0 -to 00:00:12.414 -c copy out.mp3 (which interestingly results in a different length of 12.434s) but could never get the milliseconds to be cut right.

PS. I wasn't sure whether SO was the right place to ask since it isn't technically programming related, however most of the stuff I found on ffmpeg for trimming audio files were stackoverflow questions, e. g. ffmpeg trimming videos with millisecond precision

I have the same problem did you ever find a solution to trim more precisely? — Edmund Rojas, Nov 18 '19 at 01:07
@EdmundRojas No. Unfortunately, it doesn't seem possible to trim lossy audio with high precision. See also Brad's answer — cactus, Nov 19 '19 at 19:59

score 2 · Accepted Answer · answered Jan 12 '19 at 19:28

2

You can't trim MP3 (nor most lossy codec output) with that level of precision. An MP3 frame or so of padding is added during encoding. (See also: https://wiki.hydrogenaud.io/index.php?title=Gapless, and all the hacks required to make this work.)

If you need precision timing, use something uncompressed like PCM in WAV, or a lossless compression like FLAC.

answered Jan 12 '19 at 19:28

Brad

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Very interesting answer, may i ask what about with mpeg2 ts (mp2). Might trim with total precision with this format?? – Massimo Vantaggio Jan 28 '20 at 14:03

score 0 · Answer 2 · answered Feb 19 '22 at 15:50

On Linux you can use mp3splt:

mp3splt -f mp3file.mp3 from to -o output file format

Example:

mp3splt -f "/home/audio folder/test.mp3" 0.11.89 3.25.48 -o @f_trimmed this will create a "/home/audio folder/test_trimmed.mp3"

For more info to the parameters, check the mp3splt man page here

On Windows you can use mp3DirectCut

mp3DirectCut has a GUI, but it also have command line support

ffmpeg being inprecise when trimming mp3 files

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