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I have a bunch of mp3 files with various length. I want to cut it down to 50%-60% length. Says, from 1 minute down to 30 seconds. It should be trivial using ffmpeg. But, I don't know how to determine the original length of it as a base for processing using ffmpeg.

Anyone have an idea?

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4 Answers

up vote 8 down vote accepted

With ffmpeg there's no way I know to get the length as a variable you can use on a script. But mp3info does.

mp3info -p "%S" sample.mp3   // total time in seconds
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yeah, there's no way to get length info in ffmpeg. I already stated there, I use ffmpeg only after I get the length. Anyway, thanks for the heads UP. – silent Oct 31 '09 at 3:59
BTW, %S is wrong as it only return the second part, without the minute part. For this, I use mp3info -x sample.mp3 – silent Oct 31 '09 at 4:00
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Hmm... I could check the man file, but I'm pretty sure %s (lowercase) is the one returning only the seconds part. %S (uppercase) returns total time in seconds. Do confirm that. – A Dwarf Oct 31 '09 at 4:02
Yup. Just checked. It is as I say :) Check your mp3info man page – A Dwarf Oct 31 '09 at 4:06
ups, my bad, I didn't see it was UPPERCASE, sorry. – silent Oct 31 '09 at 4:25
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up vote 4 down vote

ffmpeg will print everything it knows about the file if you don't give it any other arguments. Use grep to strip out everything but the "Duration":

$ ffmpeg -i foo.mp3 2>&1 | grep Duration
  Duration: 01:02:20.20, start: 0.000000, bitrate: 128 kb/s

You could also use mplayer. Grep for line "ID_LENGTH=":

$ mplayer -ao null -identify -frames 0 foo.mp3 2>&1 | grep ID_LENGTH
ID_LENGTH=3740.00
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$ ffmpeg -i foo.mp3 2>&1 | awk '/Duration/ { print substr($2,0,length($2)-1) }' For just the time portion – Craig Tataryn Oct 6 '10 at 18:16
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up vote 2 down vote

Interestingly the EXIFTool application gives MP3 duration as the last line!

$ exiftool somefile.mp3
ExifTool Version Number         : 7.98
File Name                       : somefile.mp3
Directory                       : .
File Size                       : 49 MB
File Modification Date/Time     : 2009:09:10 11:04:54+05:30
File Type                       : MP3
MIME Type                       : audio/mpeg
MPEG Audio Version              : 2.5
Audio Layer                     : 3
Audio Bitrate                   : 64000
Sample Rate                     : 8000
Channel Mode                    : Single Channel
MS Stereo                       : Off
Intensity Stereo                : Off
Copyright Flag                  : False
Original Media                  : True
Emphasis                        : None
ID3 Size                        : 26
Genre                           : Blues
Duration                        : 1:47:46 (approx)
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up vote 1 down vote

I personally use Mplayer to extract the information, mostly because I already have it installed and can't be bothered to install new software unnecessarily. The advantage to this is that it isn't limited to mp3 files in particular, and should work with any media file that Mplayer can handle. The following one-liner will return the track length in seconds.

mplayer -identify -ao null -vo null -frames 0 Filename.mp3 | grep ^ID_LENGTH= | cut -d = -f 2
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