[bug PyQt 5.15.2] segmentation fault using QVideoFilterRunnable

Adrian Fiergolski adrian.fiergolski at fastree3d.com
Wed Feb 17 17:14:22 GMT 2021

On 17.02.2021 17:48, Phil Thompson wrote:
> On 17/02/2021 16:32, Adrian Fiergolski wrote:
>> On 11.02.2021 11:36, Phil Thompson wrote:
>>> On 11/02/2021 09:55, Adrian Fiergolski wrote:
>>>> On 11.02.2021 at 10:48, Phil Thompson wrote:
>>>>> On 11/02/2021 09:19, Adrian Fiergolski wrote:
>>>>>> On 10.02.2021 at 23:09, Phil Thompson wrote:
>>>>>>> On 10/02/2021 17:53, Adrian Fiergolski wrote:
>>>>>>>> On 10.02.2021 18:35, Phil Thompson wrote:
>>>>>>>>> On 10/02/2021 16:30, Adrian Fiergolski wrote:
>>>>>>>>>> Hi,
>>>>>>>>>> I am getting segmentation fault using QVideoFilterRunnable. I
>>>>>>>>>> try to
>>>>>>>>>> follow the example from the documentation.
>>>>>>>>>> I am enclosing the testcase and the log from the debugger (gdb).
>>>>>>>>>> My setup: yocto (with meta-qt5 gatesgarth, PyQt 5.15.2)
>>>>>>>>>> running on
>>>>>>>>>> Cortex A-53, kernel 5.4).
>>>>>>>>>> I got the same issue with PyQt 5.13.2 on my embedded
>>>>>>>>>> platform. The
>>>>>>>>>> problem is reproducible on a PC (running Ubuntu 20.04 with
>>>>>>>>>> installed
>>>>>>>>>> qt5-default and pyqt5-dev).
>>>>>>>>>> Once the filter is commented out (case.qml:17), everything runs
>>>>>>>>>> smoothly.
>>>>>>>>>> Do you know any workaround for that? I need to process data
>>>>>>>>>> from a
>>>>>>>>>> camera in OpenCV (I wanted to do it the
>>>>>>>>>> QVideoFilterRunnable:run)
>>>>>>>>>> and
>>>>>>>>>> paint the resulting processed frame.
>>>>>>>>> I suspect that this needs hard-coded support for
>>>>>>>>> QVideoFilterRunnable
>>>>>>>>> in the same way that PyQt supports QValidator in QML.
>>>>>>>>> There is no workaround that I'm aware of.
>>>>>>>> Hi Phil,
>>>>>>>> Thank you for your reply. I am new to Qt. Could you elaborate on
>>>>>>>> your
>>>>>>>> answer?
>>>>>>> I'm not sure what you mean - PyQt would need to be enhanced to
>>>>>>> support
>>>>>>> this particular use case.
>>>>>>> Phil
>>>>>> So which use case of QVideoFilterRunnable and
>>>>>> QAbstractVideoFilter is
>>>>>> currently supported in PyQt?
>>>>> Using them from QML.
>>>>> Phil
> My apologies, I misread your question. Using them from QML is *not*
> currently supported (because of the need to hard-code support for
> QVideoFilterRunnable).
>>>> Could you point please to some example? Would it be still possible to
>>>> execute python from this QML object which would do manipulations with
>>>> the frame (OpenCV) and return a new frame to QML QVideoFilterRunnable?
>>> Sorry, I've never used OpenCV or video filters in Qt.
>>> Phil
>> Was anybody able to reproduce the bug? Has any bug ticket been created?
>> In the documentation [1] I find information that:
>> "QAbstractVideoFilter is meant to be subclassed. The subclasses are then
>> registered to the QML engine, so they can be used as a QML type."
>> Thus, how could I use QAbstractVideoFilter in QML as Phill suggested?
> If QVideoFilterRunnable can only be used from QML (I'm not familiar
> with every part of the Qt API), then you can't use it to do what you
> want with PyQt.
> Phil
Phil, sorry, but your reply is not clear to me. Could you elaborate it a
bit on them, please?

According to the documentation link I shared [1], both,
QVideoFilterRunnable and QAbstractVideoFilter can be used not only from
QML, but also from C++. Documentation gives C++ examples how to use
them. Why they can't be used in PyQt then? By adding printout to my test
case, I see that __init__ of QAbstractVideoFilter() is called properly.
Though execution never gets to createFilterRunnable(). Is it clear why?



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