[Development] New Qt Multimedia

[Lars Knoll]

> On 28 May 2021, at 10:27, Samuel Gaist <samuel.gaist at idiap.ch> wrote:
> 
> 
>> On 28 May 2021, at 10:09, Lars Knoll <lars.knoll at qt.io> wrote:
>> 
>>> On 28 May 2021, at 09:15, Alberto Mardegan <mardy at users.sourceforge.net> wrote:
>>> 
>>> Hi Lars,
>>> 
>>> On 26/05/21 15:09, Lars Knoll wrote:
>>>> The hope is that we can change that for Qt 6. To make this possible, we have changed not only parts of the public API, but completely redone its internal architecture, especially how multimedia connects to the platform specific backends. Apart from cleaning up the backend API and greatly simplifying it, I also chose to make it private and remove the plugin architecture around it. The backend is now selected at compile time, and we’re now only supporting one backend per platform.
>>> 
>>> can you please clarify what this would mean for projects (like Ubuntu
>>> Touch) which are using their own QtMultimedia plugins?
>>> Supporting one plugin per platform seems reasonable, but making the
>>> plugin API private and selecting the plugin at compile time probably
>>> means that all multimedia backends must be made part of QtMultimedia git
>>> repository, right?
>> 
>> For the moment that is correct. The reason is that it greatly simplifies maintenance of the module, something we’ve been struggling with for the whole lifetime of Qt 5.
>> 
>> Having a public API for the backend was one of the main problems that made it extremely difficult to work and maintain the module. And plugins for the backend didn’t make much sense once the backend API is private.
>> 
>> A public backend API with a BC promise is simply not an option IMO, as it will make it significantly harder to implement new functionality for Qt MM in the future.
>>> 
>>> Or is it so that the backend is selected at compile time, but it can
>>> still be dynamically loaded from a separate plugin binary?
>> 
>> No, selection is done at compile time right now.
>>> 
>>> This has the potential to make things harder to develop, especially for
>>> smaller projects like ours. I'm especially thinking of:
>> 
>> Before we go into the topics below, can we take a step back, please? I’d first like to know *why* you were developing and maintaining your own multimedia backend.
>> 
>> Cheers,
>> Lars
>> 
> 
> There might also be a need to define exactly what "multimedia backend" means here.
> 
> I have implemented several custom QCamera backends for hardware that were not accessible through the system multimedia API.
> 
> For example network cameras, AJA capture cards, BlackMagic capture cards, etc.
> 
> Would that still be possible with the Qt 6 implementation ?

How have you implemented those? If you implemented a gstreamer element for those cameras, and gst-device-monitor lists them correctly, we’ll simply pick them up.

Cheers,
Lars