cam_capture.py

'''
This module provides a function to enable video capture from screen devices such
as attached iPhones. Only macOS hosts are supported.

    enable_screen_capture_devices()

You may need QuickTime running to see the devices:

    https://stackoverflow.com/questions/48166748/coremediaio-doesnt-list-iphone-camera-unless-quicktime-is-open
'''
import ctypes


# On newer macOS, this path does not actually exist on the filesystem, but the
# underlying dlopen() call should get it from the shared cache for us.
CoreMediaIO = ctypes.cdll.LoadLibrary(
    '/System/Library/Frameworks/CoreMediaIO.framework/CoreMediaIO')


# From MacTypes.h
OSStatus = ctypes.c_int32
noErr = 0

# From CoreMediaIO.framework/CMIOHardwareSystem.h
kCMIOHardwarePropertyAllowScreenCaptureDevices = 0x79657320  # 'yes '
kCMIOObjectSystemObject = 1

# From CoreMediaIO.framework/CMIOHardwareObject.h
kCMIOObjectPropertyElementMaster = 0
kCMIOObjectPropertyScopeGlobal = 0x676c6f62  # 'glob'

CMIOObjectID = ctypes.c_uint32
CMIOObjectPropertySelector = ctypes.c_uint32
CMIOObjectPropertyScope = ctypes.c_uint32
CMIOObjectPropertyElement = ctypes.c_uint32

class CMIOObjectPropertyAddress(ctypes.Structure):
    _fields_ = [
        ('mSelector', CMIOObjectPropertySelector),
        ('mScope',    CMIOObjectPropertyScope),
        ('mElement',  CMIOObjectPropertyElement),
    ]

CMIOObjectSetPropertyData = CoreMediaIO.CMIOObjectSetPropertyData
CMIOObjectSetPropertyData.argtypes = [
    CMIOObjectID,  # objectID
    ctypes.POINTER(CMIOObjectPropertyAddress),  # address
    ctypes.c_uint32,  # qualifierDataSize
    ctypes.c_void_p,  # qualifierData
    ctypes.c_uint32,  # dataSize
    ctypes.c_void_p,  # data
]
CMIOObjectSetPropertyData.restype = OSStatus


def enable_screen_capture_devices():
    # Call API to allow screen capture devices
    addr = CMIOObjectPropertyAddress()
    addr.mSelector = kCMIOHardwarePropertyAllowScreenCaptureDevices
    addr.mScope = kCMIOObjectPropertyScopeGlobal
    addr.mElement = kCMIOObjectPropertyElementMaster

    allow = ctypes.c_uint32(1)

    err = CMIOObjectSetPropertyData(
        kCMIOObjectSystemObject,
        ctypes.byref(addr),
        0, None,
        ctypes.sizeof(allow), ctypes.byref(allow)
    )

    assert err == noErr


__all__ = [ enable_screen_capture_devices ]