This script will create mp3 sample clips.

create_mp3_samples.py

#!/usr/bin/env python
"""A utility for creating a clip of an mp3 file"""

import getopt, os, sys
from subprocess import Popen, PIPE
try:
    from mutagen.id3 import ID3
except ImportError:
    print "Missing mutagen. On Debian systems, install python-mutagen"
    sys.exit(1)


def copyid3(src, dst):
    """ Copy the id3 tag from the src file to the dst file """
    id3 = ID3(src)
    id3.save(dst, v1=0)

def mp3towav(mp3filename, wavfilename):
    """ Convert mp3filename to a wav file, wavfilename """
    pid = Popen(["mpg123", "-w", wavfilename, mp3filename], stdout=PIPE,
            stderr=PIPE)
    return pid.communicate()[0]

def cutwav(wavfilename, cutwavfilename, endtime):
    """ Cut wavfilename """
    pid = Popen(["qwavcut", "-s", endtime, "-o", cutwavfilename, wavfilename],
            stderr=PIPE, stdout=PIPE)
    return pid.communicate()[0]

def fadeoutwav(wavfilename, duration):
    """ Fade out wavfilename by duration """
    pid = Popen(["qwavfade", "-l", duration, "-o", wavfilename],
            stderr=PIPE, stdout=PIPE)
    return pid.communicate()[0]

def encodemp3(wavfilename, mp3filename, bitrate):
    """ Encode wav file wavfilename into an mp3, mp3filename """
    pid = Popen(["lame", "-b", bitrate, wavfilename, mp3filename],
            stderr=PIPE, stdout=PIPE)
    return pid.communicate()[0]

def run(outdir, endtime, fadeout, files):
    """
    Process "files". Fade them out by "fadeout" time after "endTime"
    Copy resulting samples to outdir
    """
    #make new directory to store them in
    if outdir != None:
        if not os.path.isdir(outdir):
            os.mkdir(outdir)

    #For each file
    for mp3filename in files:
        mp3filename = os.path.abspath(mp3filename)
        baseabsname, ext = os.path.splitext(mp3filename)
        basedir, basename = os.path.split(mp3filename)
        basename = os.path.splitext(basename)[0]
        #make sure it's an mp3
        if ext != '.mp3':
            break

        wavfilename = baseabsname+'.wav'
        if os.path.isfile(wavfilename):
            print "%s already exists?" % (wavfilename)
            return
        try:
            print "Working on %s" % (basename)
            #convert to wav
            mp3towav(mp3filename, wavfilename)

            #cut the wav (overwrite original is fine)
            cutwavfilename = baseabsname+'_cut_'+'.wav'
            cutwav(wavfilename, cutwavfilename, endtime)

            #fade it (overwrite original is fine)
            fadeoutwav(cutwavfilename, fadeout)

            #encode temp wav to mp3 in the new directory
            newmp3filename = os.path.join(outdir if outdir else basedir,
                    basename+'_sample.mp3')
            encodemp3(cutwavfilename, newmp3filename, '128')

            #insert id3 object
            copyid3(mp3filename, newmp3filename)
        finally:
            os.remove(wavfilename)
            os.remove(cutwavfilename)


def usage():
    """ print out usage for command line use """
    print "createMP3Snippet.py [-o|--outdir <output directory>] [-h|--help]"
    print "                    [-c|--cut <point to cut off>]"
    print "                    [-f|--fadeout <fade out duration>]"
    print "                    <file pattern to process>"

def main():
    """ main program, only in here should we call sys.exit """
    try:
        opts, args = getopt.getopt(sys.argv[1:],
                "o:hc:f:", ["outdir", "help", "cut", "fadeout"])
    except getopt.GetoptError, err:
        print str(err)
        usage()
        sys.exit(2)
    outdir = None
    cut = "30s"
    fadeout = "5s"
    for option, argument in opts:
        if option in ("-o", "--outdir"):
            outdir = argument
        elif option in ("-h", "--help"):
            usage()
            sys.exit()
        elif option in ("-c", "--cut"):
            cut = argument
        elif option in ("-f", "--fadeout"):
            fadeout = argument
        else:
            assert False, "unhandled option"
    run(outdir, cut, fadeout, args)

if __name__ == "__main__":
    main()