Getting Started¶
To get started with PyOgg, make sure you’ve followed the installation instructions (see Installation). The next section gives a very easy introduction for a first project with PyOgg.
First Project¶
As a first project, let’s create a program that outputs the duration of an Opus-encoded audio file.
We’ll make it easy for ourselves and use NumPy. Make sure you’ve installed it. To install NumPy run the command:
pip install numpy
Next, create a directory (folder) to save our work.
Download the example OggOpus file
and save it as left-right-demo-5s.opus in the directory you just
created. This file is exactly five seconds long.
Create a Python program in your favourite editor, let’s call the file
getting_started.py.
As the first lines of your file, Import the PyOgg and NumPy libraries with the lines:
import numpy
import pyogg
We’ll now use the PyOgg class OpusFile to read the example OggOpus
file into memory:
filename = "left-right-demo-5s.opus"
opus_file = pyogg.OpusFile(filename)
The contents of the file, stored in PCM can now be
obtained using the method as_array().
The method returns a NumPy array containing all the audio in the file.
NumPy provides a shape attribute that gives us the size of the
array. In our case, this will give us (240000,2). What do these
numbers mean?
The second number in the tuple is easy to understand: the 2 tells
us there are two channels, thus this file is in stereo.
But what about the first number, the 240,000? That’s the number of
samples per channel. The quality of an audio recording is partially
governed by the number of samples recorded per second. Opus-encoded
recordings are typically saved at 48,000 samples per second. We can
get this number from opus_file.frequency.
Now we have enough information to calculate the duration of the audio:
pcm = opus_file.as_array()
duration_seconds = pcm.shape[0] / opus_file.frequency
print("Audio duration (seconds):", duration_seconds)
Note: If you’re not using Python 3, you will have to adapt the print
command by removing the parentheses in that line.
Run your Python program from within the directory we created at the start and you should see something similar to:
$ python getting_started.py
Audio duration (seconds): 5.0
Below is the complete example:
import numpy
import pyogg
filename = "left-right-demo-5s.opus"
opus_file = pyogg.OpusFile(filename)
pcm = opus_file.as_array()
duration_seconds = pcm.shape[0] / opus_file.frequency
print("Audio duration (seconds):", duration_seconds)