Read amplitude data from mp3

I am trying to write some code that will extract the amplitude data from an mp3 as a function of time. I wrote up a rough version on MATLAB a while back using this function: http://labrosa.ee.columbia.edu/matlab/mp3read.html However I am having trouble finding a Python equivalent.

I've done a lot of research, and so far I've gathered that I need to use something like mpg321 to convert the .mp3 into a .wav. I haven't been able to figure out how to get that to work.

The next step will be reading the data from the .wav file, which I also haven't had any success with. Has anyone done anything similar or could recommend some libraries to help with this? Thanks!

Solution

You can use the subprocess module to call mpg123:

import subprocess
import sys

inname = 'foo.mp3'
outname = 'out.wav'
try:
    subprocess.check_call(['mpg123', '-w', outname, inname])
except CalledProcessError as e:
    print e
    sys.exit(1)

For reading wav files you should use the wave module, like this:

import wave
import numpy as np

wr = wave.open('input.wav', 'r')
sz = 44100 # Read and process 1 second at a time.
da = np.fromstring(wr.readframes(sz), dtype=np.int16)
wr.close()
left, right = da[0::2], da[1::2]

After that, left and right contain the samples of the same channels.

You can find a more elaborate example here.