All the examples I can find are mono, with CHANNELS = 1. How do you read stereo or multichannel input using the callback method in PyAudio and convert it into a 2D NumPy array or multiple 1D arrays?
For mono input, something like this works:
def callback(in_data, frame_count, time_info, status): global result global result_waiting if in_data: result = np.fromstring(in_data, dtype=np.float32) result_waiting = True else: print('no input') return None, pyaudio.paContinue stream = p.open(format=pyaudio.paFloat32, channels=1, rate=fs, output=False, input=True, frames_per_buffer=fs, stream_callback=callback)
But does not work for stereo input, the result array is twice as long, so I assume the channels are interleaved or something, but I can't find documentation for this.
It appears to be interleaved sample-by-sample, with left channel first. With signal on left channel input and silence on right channel, I get:
result = [0.2776, -0.0002, 0.2732, -0.0002, 0.2688, -0.0001, 0.2643, -0.0003, 0.2599, ...
So to separate it out into a stereo stream, reshape into a 2D array:
result = np.fromstring(in_data, dtype=np.float32) result = np.reshape(result, (frames_per_buffer, 2))
Now to access the left channel, use result[:, 0], and for right channel, use result[:, 1].
def decode(in_data, channels): """ Convert a byte stream into a 2D numpy array with shape (chunk_size, channels) Samples are interleaved, so for a stereo stream with left channel of [L0, L1, L2, ...] and right channel of [R0, R1, R2, ...], the output is ordered as [L0, R0, L1, R1, ...] """ # TODO: handle data type as parameter, convert between pyaudio/numpy types result = np.fromstring(in_data, dtype=np.float32) chunk_length = len(result) / channels assert chunk_length == int(chunk_length) result = np.reshape(result, (chunk_length, channels)) return result def encode(signal): """ Convert a 2D numpy array into a byte stream for PyAudio Signal should be a numpy array with shape (chunk_size, channels) """ interleaved = signal.flatten() # TODO: handle data type as parameter, convert between pyaudio/numpy types out_data = interleaved.astype(np.float32).tostring() return out_data
