How to stop a stream.write function in sounddevice

Question

Is it possible to stop a stream.write function before the buffer is consumed completely? When I try to do so, the sound is stopped, but the stream.write function never returns.

This is a working example of how I want to use a small class to play pure tone sounds without blocking the main thread.

import time
import sounddevice as sd
import numpy as np
from threading import Thread

toneduration = 10
samplerate = 44100
frequency = 440
amplitude = 0.5

sd.default.device = 1
sd.default.samplerate = samplerate
sd.default.channels = 2

class Sound(Thread):
    def __init__(self):
        Thread.__init__(self)
        self.stream = sd.OutputStream()
        self.stream.start()

        vector1 = np.linspace(0, toneduration, toneduration * samplerate)
        vector2 = amplitude * np.sin(2 * np.pi * frequency * vector1)
        vector3 = np.array([vector2, vector2])
        self.soundVector = np.ascontiguousarray(vector3.T, dtype=np.float32)

    def run(self):
        self.stream.write(self.soundVector)
        print('end')

sound = Sound()
sound.start()
time.sleep(3)
sound.stream.close()

I can play sounds of a given duration, but if I manually stop the stream using stream.close() the function doesn't return (the print('end') message is never displayed and the thread doesn't finish)

Do I have to use callback instead? In that case, how am I supposed to fill the buffer with a numpy array? I read the code examples in the documentation but I couldn’t figure it out how to do that.

score 0 · Accepted Answer · answered Oct 06 '19 at 15:40

I guess the simplest way would be to use the play() function, which per default starts playback in the background (using a callback function called from a separate thread created by the underlying PortAudio library). You can then use the stop() function to stop playback.

If you need something more complicated than a simple playback of a NumPy array, you can implement your own callback function. As an example, you can look at the implementation of the play() function or at the examples, e.g. play_long_file.py.

As you mentioned, you can also use the so-called "blocking" API (using the write() method).

Either way, you would typically split your audio data into a series of blocks. This way, you can arrange for the playback to be stopped after any one of the blocks. This is also what the play() function does internally.

How to stop a stream.write function in sounddevice

1 Answers1