How to crop a mp3 from x to x+n using ffmpeg?

Following this question I decided to use ffmpeg to crop MP3s. On another question I found this way of doing it:

ffmpeg -t 30 -acodec copy -i inputfile.mp3 outputfile.mp3

The problem is that I don't want to crop the first 30 seconds, I want to crop from x to x+n, like from 30s to 100s. How would I go and do this?

I'm reading the man for ffmpeg but this is not really straightforward, especially since I just discovered about ffmpeg and I'm not familiar with audio/video editing softwares, so any pointers would be appreciated.

Take a look at the -t and -ss arguments. They should do what you want.

> -t duration > > Restrict the transcoded/captured video > sequence to the duration specified in > seconds. hh:mm:ss[.xxx] syntax is also > supported.
> >-ss position' > > Seek to given time position in seconds. > hh:mm:ss[.xxx] syntax is also supported.

For example, ffmpeg -ss 30 -t 70 -i inputfile.mp3 -acodec copy outputfile.mp3 should do the trick for the range you mentioned (30s-100s).

To expand a bit on Michael Madsens' Answer:

I've found either of the following satisfactory for trimming my audio files:

• ffmpeg -ss <start position>-t<duration> -i inputfile -c:a copy outputfile
• ffmpeg -ss <start position>-i inputfile -t<duration> -c:a copy outputfile

Note: -acodec is an alias for codec:a which can be specified also as c:a

As specified in the Main Options FFMPEG Documentation

-t duration (input/output)

• When used as an input option (before -i), limit the duration of data read from the input file.
• When used as an output option (before an output url), stop writing the output after its duration reaches duration.

-ss position (input/output)

• When used as an input option (before -i), seeks in this input file to position.
• When used as an output option (before an output url), decodes but discards input until the timestamps reach position.

duration and position follow the Time Duration Syntax :

• [-][HH:]MM:SS[.m...] or [-]S+[.m...][s|ms|us]

Side Note: An answer on How to detect intervals of silence with FFMPEG may also be of interest.

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Differences between seeking and duration as input or output

> Note that in most formats it is not possible to seek exactly, so ffmpeg will seek to the closest seek point before position. When transcoding and -accurate_seek is enabled (the default), this extra segment between the seek point and position will be decoded and discarded. When doing stream copy or when -noaccurate_seek is used, it will be preserved.

I did a couple Tests on the following file:

Input #0, mp3, from 'test16s.mp3':
  Duration: 00:00:16.20, start: 0.025057, bitrate: 128 kb/s
    Stream #0:0: Audio: mp3, 44100 Hz, stereo, fltp, 128 kb/s

Aligned the outputs in Audacity in comparison to the original and got the following:

• ffmpeg -ss 3 -t 5 -i test16s.mp3 -c:a copy out.mp3
  • Start: 3s+00756samples (3.017142857s)
  • End: 8s+02062samples (8.04675737s)
  • Duration : 5s+01306samples (5.029614512s)
• ffmpeg -ss 3 -i test16s.mp3 -t 5 -c:a copy out.mp3
  • Start: 3s+00756samples (3.017142857s)
  • End: 8s+00910samples (8.020634921s)
  • Duration : 5s+00154samples (5.003492063s)
• ffmpeg -i test16s.mp3 -ss 3 -t 5 -c:a copy out.mp3
  • Warning: This created a file that some mp3 decoders gave error on attempting to open.
  • Start: 2s+42184samples (2.956553288s)
  • End: 8s+01071samples (8.024285714s)
  • Duration : 5s+02987samples (5.067732426s)
• ffmpeg -t 5 -i test16s.mp3 -ss 3 -c:a copy out.mp3
  • Warning: This created a file that some mp3 decoders gave error on attempting to open.
  • Start: 2s+42184samples (2.956553288s)
  • End: 5s+02043samples (5.046326531s)
  • Duration : 2s+03959samples (2.089773243)

In an attempt to get to see the seek jump I found interesting results using :

• ffmpeg -ss <secs> -i test16s.mp3 -t 5 -c:a copy out.mp3

  • <secs> = 3, 2.99, 2.98, 2.97
    • Start: 3s+00756samples (3.017142857s), Duration:5s+00154
  • <secs> = 2.96
    • Start: same as above, Duration: 4s+41951
  • <secs> = 2.95
    • Start: 2s+43704 (2.991020408), End:7s+42707 Duration:4s+43103
  • <secs> = 2.94,2.93
    • Start: same as above, Duration: 4s+41951
  • <secs> = 2.92
    • Start: 2s+42552 (2.964897959s), Duration: 4s+43103

• ffmpeg -ss <secs> -t 5 -i test16s.mp3 -c:a copy out.mp3

  • <secs> = 3
    • Start: 3s+00756 (3.017142857s), Duration:5s+01306 (5.029614512s)
  • <secs> = 2.99, 2.98, 2.97
    • Start: same, Duration: 5s+00155
  • <secs> = 2.96
    • Start: same, Duration: 4s+43103
  • <secs> = 2.95
    • Start: 2s+43704 (2.991020408), End:7s+43859 Duration:5s+00155
  • <secs> = 2.94,2.93
    • Start: same, Duration: 4s+43103
  • <secs> = 2.92
    • Start: 2s+42552 (2.964897959s), Duration: 5s+00155

Concluding that with a Stream Copy, appears as if the minimal seek resolution in my specific file ,(Audio: mp3, 44100 Hz, stereo, fltp, 128 kb/s), was:

• Seek Step of : 1152 samples, 26.122449 ms
• Seek position Error of up to 70 ms