I’m trying to read, in near-realtime, the volume coming from the audio of a USB microphone in Python.

I have the pieces, but can’t figure out how to put it together.

If I already have a .wav file, I can pretty simply read it using wavefile:

from wavefile import WaveReader

with WaveReader("/Users/rmartin/audio.wav") as r:
    for data in r.read_iter(size=512):
        left_channel = data[0]
        volume = np.linalg.norm(left_channel)
        print volume

This works great, but I want to process the audio from the microphone in real-time, not from a file.

So my thought was to use something like ffmpeg to PIPE the real-time output into WaveReader, but my Byte knowledge is somewhat lacking.

import subprocess
import numpy as np

command = ["/usr/local/bin/ffmpeg",
            '-f', 'avfoundation',
            '-i', ':2',
            '-t', '5',
            '-ar', '11025',
            '-ac', '1',
            '-acodec','aac', '-']

pipe = subprocess.Popen(command, stdout=subprocess.PIPE, bufsize=10**8)
stdout_data = pipe.stdout.read()
audio_array = np.fromstring(stdout_data, dtype="int16")

print audio_array

That looks pretty, but it doesn’t do much. It fails with a [NULL @ 0x7ff640016600] Unable to find a suitable output format for ‘pipe:’ error.

I assume this is a fairly simple thing to do given that I only need to check the audio for volume levels.

Anyone know how to accomplish this simply? FFMPEG isn’t a requirement, but it does need to work on OSX & Linux.

Thanks to @Matthias for the suggestion to use the sounddevice module. It’s exactly what I need.

For posterity, here is a working example that prints real-time audio levels to the shell:

# Print out realtime audio volume as ascii bars

import sounddevice as sd
import numpy as np

def print_sound(indata, outdata, frames, time, status):
    volume_norm = np.linalg.norm(indata)*10
    print ("|" * int(volume_norm))

with sd.Stream(callback=print_sound):
    sd.sleep(10000)

enter image description here

Python 3 user here
I had few problems to make that work so I used:
https://python-sounddevice.readthedocs.io/en/0.3.3/examples.html#plot-microphone-signal-s-in-real-time
And I need to install sudo apt-get install python3-tk for python 3.6 look Tkinter module not found on Ubuntu
Then I modified script:

#!/usr/bin/env python3
import numpy as np
import sounddevice as sd

duration = 10 #in seconds

def audio_callback(indata, frames, time, status):
   volume_norm = np.linalg.norm(indata) * 10
   print("|" * int(volume_norm))


stream = sd.InputStream(callback=audio_callback)
with stream:
   sd.sleep(duration * 1000)

And yes it working 🙂