mp3info -p "%S" sample.mp3 // total time in seconds

• Worth noting that this only provides the length as an Integer. So may not be accurate enough for some use cases.
• Best answer as it works even with Average or Variable Bitrate MP3
• Add \n to print new line also. > mp3info -p "%S\n" sample.mp3 // total time in seconds

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

ffmpeg -i foo.mp3 2>&1 | awk '/Duration/ { print substr($2,0,length($2)-1) }' For just the time portion

To sum the length of a set of MP3 files, you can use something like TOTLENGTH=0;
for f in *.mp3; do LENGTH=$(mplayer -ao null -identify -frames 0 "$f"
2>&1 | awk -F= '/ID_LENGTH/ {print $2}' | awk -F. '{print $1}');
TOTLENGTH=$(($TOTLENGTH + $LENGTH)); done; echo $TOTLENGTH to print the total length of the audio in all files, in seconds. It can probably be done more efficiently, but since I wrote it as a one-off, it was good enough for my needs. (The second awk invocation strips off decimals, so the result isn't 100% accurate, but again, good enough for my needs.)

Beware of ffmpeg's -analyzeduration flag. Basically, the numbers it reports are estimates after a certain point in order to save CPU.

Using an Average Bitrate MP3, ffmpeg reports an incorrect duration along with this warning Estimating duration from bitrate, this may be inaccurate. I think this answer is valid only with Constant Bitrate MP3.

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)

Just another way to get the duration only using ffmpeg and grep:

# ffmpeg -i rara.mp3 2>&1 |grep -oP "[0-9]{2}:[0-9]{2}:[0-9]{2}.[0-9]{2}"
00:03:49.12

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

You can use ffmpeg to get duration of file. Just use:

ffmpeg -i <infile> 2>&1 | grep "Duration" | cut -d ' ' -f 4 | sed s/,//

The solutions using ffmpeg strike me as slightly fragile, since they are parsing output that isn't quite designed as an interface. That said they will probably continue to work for several years regardless.

ffmpeg comes with a tool ffprobe to get information about audio files (lots of formats, including mp3), and can produce machine readable output. The following command gets the song duration.

ffprobe -show_streams -print_format json song.mp3 -v fatal | jq '.streams[0].duration'

• You can just do ffprobe -show_entries stream=duration -of compact=p=0:nk=1 -v fatal song.mp3

I had the same problem and found the mplayer command (goldPseudo) worked well, but I subsequently discovered that if you open an album in RhythmBox you will see its status line gives the number of tracks, total play time and disc size.