https://stackoverflow.com/a/45483843/6911112

is_windows_playing_sound.py

# SPDX-License-Identifier: MIT

from ctypes import c_int, POINTER, c_void_p, byref, c_float
from ctypes.wintypes import DWORD
from comtypes import GUID, IUnknown, STDMETHOD, HRESULT, COMMETHOD, CoCreateInstance

EDataFlow_eRender = 0
ERole_eMultimedia = 1

CLSID_MMDeviceEnumerator = GUID('{BCDE0395-E52F-467C-8E3D-C4579291692E}')

class IMMDevice(IUnknown):
    _iid_ = GUID('{D666063F-1587-4E43-81F1-B948E807363F}')
    _methods_ = [
        COMMETHOD([], HRESULT, 'Activate',
        (['in'], POINTER(GUID), 'iid'),
        (['in'], DWORD, 'dwClsCtx'),
        (['in'], c_void_p, 'pActivationParams'),
        (['out'], POINTER(c_void_p), 'ppInterface'))
        # The rest is not defined/needed
    ]

    def activate(self, interface, clsctx=0):
        ptr = POINTER(interface)()
        iid = interface._iid_
        self.__com_Activate(byref(iid), clsctx, None, ptr)
        return ptr

class IMMDeviceEnumerator(IUnknown):
    _iid_ = GUID('{A95664D2-9614-4F35-A746-DE8DB63617E6}')
    _methods_ = [
        STDMETHOD(HRESULT, 'EnumAudioEndpoints'), # Unused
        COMMETHOD([], HRESULT, 'GetDefaultAudioEndpoint',
        (['in'], c_int, 'dataFlow'),
        (['in'], c_int, 'role'),
        (['out'], POINTER(POINTER(IMMDevice)), 'ppEndpoint'))
        # The rest is not defined/needed
    ]

    def get_default_audio_endpoint(self, data_flow, role):
        ptr = POINTER(IMMDevice)()
        self.__com_GetDefaultAudioEndpoint(data_flow, role, ptr)
        return ptr

class IAudioMeterInformation(IUnknown):
    _iid_ = GUID('{C02216F6-8C67-4B5B-9D00-D008E73E0064}')
    _methods_ = [
        # HRESULT GetPeakValue([out] float *pfPeak);
        COMMETHOD(['propget'], HRESULT, 'peak_value',
        (['retval', 'out'], POINTER(c_float), 'pfPeak'))
        # The rest is not defined/needed
    ]

def is_windows_playing_sound():
    enumerator = CoCreateInstance(CLSID_MMDeviceEnumerator, IMMDeviceEnumerator)
    speakers = enumerator.get_default_audio_endpoint(EDataFlow_eRender, ERole_eMultimedia)
    meter = speakers.activate(IAudioMeterInformation)
    value = meter.peak_value;
    print(value)
    return value > 1e-08

if __name__ == '__main__':
    print(f'is_windows_playing_sound(): {is_windows_playing_sound()}')