I restarted my iPad mini and it runs OK now.
Thank you very much for all of your help.

Thank you very much for checking my code.

@JonB Pythonista 3.2 on iPad mini 5. This code says:

Pythonista version 3.2 (320000) running Python 3.6.1 on iOS 12.3.1 on a 64-bit iPad11,1 with a screen size of (1024 x 768) * 2

.encoding is:

>>> _device.setActiveVideoMinFrameDuration_.encoding
b'v40@0:8{?=qiIq}16'

@cvp I assume 3/30 = 10 FPS. It gave the same error without the line dur.value *= 3.

This error may be specific on iPad mini.

Thank you very much for all of your advices. I still have no luck.

I ran the following code:

from ctypes import *
from objc_util import *

class CMTime(Structure):
  _fields_ = [('value', c_int64), ('timescale', c_int32), ('flags', c_uint32), ('epoch', c_int64)]

AVCaptureDevice = ObjCClass('AVCaptureDevice')

_device = AVCaptureDevice.defaultDeviceWithDeviceType_mediaType_position_(
  'AVCaptureDeviceTypeBuiltInWideAngleCamera', 'vide', 1)

dur = _device.activeVideoMinFrameDuration(restype=CMTime, argtypes=[])
dur.value *= 3
_device.lockForConfiguration_(None)
_device.setActiveVideoMinFrameDuration_(dur, restype=None, argtypes=[CMTime])
_device.unlockForConfiguration()

And I got error:

Traceback (most recent call last):
  File "/private/var/mobile/Containers/Shared/AppGroup/94D43082-190D-4454-9A0E-256D7C4B8046/Pythonista3/Documents/test.py", line 15, in <module>
    _device.setActiveVideoMinFrameDuration_(dur, restype=None, argtypes=[CMTime])
  File "/var/containers/Bundle/Application/F1D3A05F-66E7-4AD5-8569-D61994DF7737/Pythonista3.app/Frameworks/Py3Kit.framework/pylib/site-packages/objc_util.py", line 897, in __call__
    res = objc_msgSend(obj.ptr, sel(self.sel_name), *args)
ctypes.ArgumentError: argument 3: <class 'TypeError'>: expected __Structure instance instead of CMTime

activeVideoMinFrameDuration is a property. Is there any way to specify argument types of a setter?

Hello forum members. Will you tell me how to set activeVideoMinFrameDuration?

I tried the following code:

from objc_util import *

AVCaptureDevice = ObjCClass('AVCaptureDevice')

_device = AVCaptureDevice.defaultDeviceWithDeviceType_mediaType_position_(
  'AVCaptureDeviceTypeBuiltInWideAngleCamera', 'vide', 1)

dur = _device.activeVideoMinFrameDuration()
dur.a *= 3
_device.setActiveVideoMinFrameDuration(dur)

I got error:

Traceback (most recent call last):
  File "/var/mobile/Containers/Shared/AppGroup/94D43082-190D-4454-9A0E-256D7C4B8046/Pythonista3/Documents/test.py", line 10, in <module>
    _device.setActiveVideoMinFrameDuration(dur)
  File "/var/containers/Bundle/Application/F1D3A05F-66E7-4AD5-8569-D61994DF7737/Pythonista3.app/Frameworks/Py3Kit.framework/pylib/site-packages/objc_util.py", line 803, in __call__
    return method(*ordered_args, **kw)
  File "/var/containers/Bundle/Application/F1D3A05F-66E7-4AD5-8569-D61994DF7737/Pythonista3.app/Frameworks/Py3Kit.framework/pylib/site-packages/objc_util.py", line 897, in __call__
    res = objc_msgSend(obj.ptr, sel(self.sel_name), *args)
ctypes.ArgumentError: argument 3: <class 'TypeError'>: expected __Structure instance instead of __Structure

I have read the following topic: https://forum.omz-software.com/topic/2031/videos, but I have had no success so far.