[bug PyQt 5.15.2] segmentation fault using QVideoFilterRunnable

[Phil Thompson]

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