Trying to plot the audio data stored in audio_common_msgs

Question

I am loading in audio data collected in a rosbag using the audio_common_msgs package to collect the data.

I now want to plot the frequency vs time plot of the audio.

I have seen ways to convert the data to mp3, but I am not sure how to plot the data after converting to mp3?

Is there a way to directly store the audio data and plot it using some Python package? Or even after storing it as an mp3 or WAV file?

Answer 1

Extracting the data

From this answer to get the amplitude data from an mp3 audio files using python, use pydub:

from pydub import AudioSegment

sound = AudioSegment.from_mp3("test.mp3")

# get raw audio data as a bytestring
raw_data = sound.raw_data
# get the frame rate
sample_rate = sound.frame_rate
# get amount of bytes contained in one sample
sample_size = sound.sample_width
# get channels
channels = sound.channels

Plotting the data

Look at Matplotlib for plotting data in Python. It's very comprehensive (almost dauntingly so).

However, there are loads of tutorials and examples out there. I used this (amongst other things) to learn it: Python Plotting With Matplotlib (Guide).

You can probably skim and skip the super-funky examples and just get a basic X-Y plot displayed pretty quickly.

StackOverflow also has a number of simple examples provided in the answers.

Putting them together - an example

From this answer to Plot spectogram from mp3:

from pydub import AudioSegment
import matplotlib.pyplot as plt
from scipy.io import wavfile
from tempfile import mktemp

mp3_audio = AudioSegment.from_file('speech.mp3', format="mp3")  # read mp3
wname = mktemp('.wav')  # use temporary file
mp3_audio.export(wname, format="wav")  # convert to wav
FS, data = wavfile.read(wname)  # read wav file
plt.specgram(data, Fs=FS, NFFT=128, noverlap=0)  # plot
plt.show()