pydub_mixer.py

from pydub import AudioSegment
import numpy as np

class Mixer:
    def __init__(self):
        self.parts = []

    def __len__(self):
        parts = self._sync()
        seg = parts[0][1]
        frame_count = max(offset + seg.frame_count() for offset, seg in parts)
        return int(1000.0 * frame_count / seg.frame_rate)

    def overlay(self, sound, position=0):
        self.parts.append((position, sound))
        return self

    def _sync(self):
        positions, segs = zip(*self.parts)

        frame_rate = segs[0].frame_rate
        array_type = segs[0].array_type

        offsets = [int(frame_rate * pos / 1000.0) for pos in positions]
        segs = AudioSegment.empty()._sync(*segs)
        return list(zip(offsets, segs))

    def append(self, sound):
        self.overlay(sound, position=len(self))

    def to_audio_segment(self):
        parts = self._sync()
        seg = parts[0][1]
        channels = seg.channels

        frame_count = max(offset + seg.frame_count() for offset, seg in parts)
        sample_count = int(frame_count * seg.channels)

        # We use a larger data type so that clipping doesn't cause data loss
        output = np.zeros(sample_count, dtype="int32")
        for offset, seg in parts:
            sample_offset = offset * channels
            samples = np.frombuffer(seg.get_array_of_samples(), dtype="int16")
            start = sample_offset
            end = start + len(samples)
            output[start:end] += samples

        # The audio is then normalized to occupy the full "height" again
        return seg._spawn(output, overrides={"sample_width": 4}).normalize(headroom=0.0)

Hey, thanks for your great work :)

I found a small bug within your code, where certain pydub Audiosegments (directly read as .wav) caused errors. I fixed this issue by replacing samples = np.frombuffer(seg.get_array_of_samples(), dtype="int16") with samples = np.frombuffer(seg.get_array_of_samples(), dtype="int32").

Hi @Peda1996! You're absolutely right. The code currently does not account for 32-bit WAV, only 16-bit! I only bothered making it support that because it was enough for what I needed, but I do eventually plan to fix this. :)

Your change is fine! Just keep in mind that the code is using an "oversized" array in order to account for clipping. So if you changed samples to 32-bit, you probably should change output to be 64-bit; otherwise, clipping may occur as it's adding the samples.

Thank you for using the script; glad it got to be useful 😄

Well, 64-bit output won't work that well with pydub, I think. So one possibility would be to rescale the 32 Bit Input Array to 16 bit (in this case it's also automatically normalized)?
samples = np.frombuffer(seg.get_array_of_samples(), dtype="int32")
samples = np.int16(samples/np.max(np.abs(samples)) * 32767)

If normalizing isn't wanted, one could also just use the maximal 32Bit integer Value as a dividend:
samples = np.int16(samples/2147483647 * 32767)

16 bit int max value: 32767
32 bit int max value: 2147483647