Introduction to PyAudio

A convenient audio package in Python

Presentation by Jean Cruypenynck/@nonatomiclabs

Why?

• Audio is fun…
• but always a problem!

Audio + Computers = 💔 ?

• huge variety of devices, standards, formats, etc.
• huge variety of native APIs, often complex

Audio + Python = 💔 ?

• no “correct” audio module in standard library
• some attempts: winaudio, Carbon.snd, sunaudiodev, ossaudiodev, …
  • platform-dependent
  • limited features
  • often deprecated

PortAudio

A famous C library to deal with audio

Famous because:

• cross-platform
• open-source
• tried and tested
• simple interface to deal with audio

PortAudio

PyAudio

• provides Python bindings for PortAudio
• allows to play audio
• allows to record audio
• open-source
• cross-platform

Classes

1. pyaudio.PyAudio

   • ​start/terminate PortAudio
   • open/close streams
   • access audio devices

2. pyaudio.Stream

   • ​real audio processing is here!

Basic PyAudio flow

open()

parameters​

• rate: sampling frequency (usually 44.1/48 kHz)
• format: bit depth (usually 16/24 bits)
• channels: number of audio channels
• input: to use the stream as input
• output: to use the stream as output
• input_device_index: input device to use
• output_device_index: output device to use
• frames_per_buffer: length of the audio buffer
• start: to start the stream directly after opening
• input_host_api_specific_stream_info: …
• output_host_api_specific_stream_info: …
• stream_callback: function used to process audio

stream_callback

The

def callback(in_data, frame_count,
             time_info, status_flags):
    # PROCESSING
    out_data = in_data
    return (out_data, pyaudio.PaContinue)

Function called every time audio is needed
(full input buffer/empty output buffer)

Example 1

Audio level meter

Initialisation

import sys
import pyaudio
import math
import struct
import time

# Instantiate PyAudio
p = pyaudio.PyAudio()

Stream creation & shutting

# Open stream using callback
stream = p.open(format=pyaudio.paInt16,
                channels=1,
                rate=48000,
                frames_per_buffer=1024,
                input=True,
                output=True,
                stream_callback=callback)

# Close the stream after 10 seconds
time.sleep(10)
stream.close()

Callback definition

def callback(in_data, frame_count, time_info, status):
    levels = []
    for _i in range(1024):
        levels.append(struct.unpack('<h', in_data[_i:_i + 2])[0])
    avg_chunk = sum(levels)/len(levels)
    
    print_audio_level(avg_chunk, time_info['current_time'])
    
    return (in_data, pyaudio.paContinue)

Example 2

Audio player

Initialisation

import pyaudio
import wave
import sys

BUFFER_SIZE = 1024

# Opening audio file as binary data
wf = wave.open(sys.argv[1], 'rb')

# Instantiate PyAudio
p = pyaudio.PyAudio()

Stream creation & shutting

file_sw = wf.getsampwidth()

stream = p.open(format=p.get_format_from_width(file_sw),
                channels=wf.getnchannels(),
                rate=wf.getframerate(),
                output=True)

data = wf.readframes(BUFFER_SIZE)

while data != '':
    stream.write(data)
    data = wf.readframes(BUFFER_SIZE)

stream.stop_stream()
stream.close()

p.terminate()

Other applications

• audio recorder
• frequency recognition
• filtering
• audio effects
• …

all real-time!

Thank you for your attention!

nonatomiclabs.com