Record speakers output with PyAudio

Question

I'm trying to record the output from my computer speakers with PyAudio.
I tried to modify the code example given in the PyAudio documentation, but it doesn't work.

Technically, there's no error. I obtain the file output.wav and I can open it, but there's no sound. On Audacity, I can only see a straight line.

What's going wrong?

import pyaudio
import wave

CHUNK = 1024
FORMAT = pyaudio.paInt16
CHANNELS = 2
RATE = 44100
RECORD_SECONDS = 5
WAVE_OUTPUT_FILENAME = "output.wav"

p = pyaudio.PyAudio()

SPEAKERS = p.get_default_output_device_info()["hostApi"] #The part I have modified

stream = p.open(format=FORMAT,
                channels=CHANNELS,
                rate=RATE,
                input=True,
                frames_per_buffer=CHUNK,
                input_host_api_specific_stream_info=SPEAKERS) #The part I have modified

print("* recording")

frames = []

for i in range(0, int(RATE / CHUNK * RECORD_SECONDS)):
    data = stream.read(CHUNK)
    frames.append(data)

print("* done recording")

stream.stop_stream()
stream.close()
p.terminate()

wf = wave.open(WAVE_OUTPUT_FILENAME, 'wb')
wf.setnchannels(CHANNELS)
wf.setsampwidth(p.get_sample_size(FORMAT))
wf.setframerate(RATE)
wf.writeframes(b''.join(frames))
wf.close()

Answer 1

In case someone is still stumbling over this like me, I found a PyAudio fork to record the output on windows.

Explanation:

The official PyAudio build isn't able to record the output. BUT with Windows Vista and above, a new API, WASAPI was introduced, which includes the ability to open a stream to an output device in loopback mode. In this mode the stream will behave like an input stream, with the ability to record the outgoing audio stream.

To set the mode, one has to set a special flag (AUDCLNT_STREAMFLAGS_LOOPBACK). Since this flag is not supported in the official build one needs to edit PortAudio as well as PyAudio, to add loopback support.

New option:

"as_loopback":(true|false)

Answer 2

I got to record my speaker output with pyaudio with some configuration and code from pyaudio's documentation.

Code

"""PyAudio example: Record a few seconds of audio and save to a WAVE file."""

import pyaudio
import wave

CHUNK = 1024
FORMAT = pyaudio.paInt16
CHANNELS = 2
RATE = 44100
RECORD_SECONDS = 5
WAVE_OUTPUT_FILENAME = "output.wav"

p = pyaudio.PyAudio()

stream = p.open(format=FORMAT,
                channels=CHANNELS,
                rate=RATE,
                input=True,
                frames_per_buffer=CHUNK)

print("* recording")

frames = []

for i in range(0, int(RATE / CHUNK * RECORD_SECONDS)):
    data = stream.read(CHUNK)
    frames.append(data)

print("* done recording")

stream.stop_stream()
stream.close()
p.terminate()

wf = wave.open(WAVE_OUTPUT_FILENAME, 'wb')
wf.setnchannels(CHANNELS)
wf.setsampwidth(p.get_sample_size(FORMAT))
wf.setframerate(RATE)
wf.writeframes(b''.join(frames))
wf.close()

Configuration

First, with pulseaudio running, create a loopback device:

pacmd load-module module-loopback latency_msec=5

Then set the default (fallback) to this loopback device in pavucontrol:

Then you can start the script, wait 5 seconds, and you should have an output.wav.