Why does QMediaGaplessPlaybackControl not exist?

Question

I have modified the Qt Media Player Example, trying to get QMediaGaplessPlaybackControl for a crossfade effect.

Here is my code:

auto service = m_player->service();
auto cc = service->requestControl("org.qt-project.qt.mediaplayercontrol/5.0");
Q_ASSERT(cc != nullptr);
QMessageBox::information(this, "", cc->metaObject()->className());
QMediaGaplessPlaybackControl* control = qobject_cast<QMediaGaplessPlaybackControl*>(cc);
Q_ASSERT(control != nullptr);

The problem is, that when I request the control, a nullptr is returned. Does anyone know why?

I'm using Qt 5.11 on Windows with MSVC compiler.

scopchanov · Accepted Answer · 2018-09-08T13:50:54.753

1

The documentation of QMediaService is explicit about how to obtain a pointer to the media service's QMediaControl implementation:

auto cc = qobject_cast<QMediaPlayerControl *>(service->requestControl("org.qt-project.qt.mediaplayercontrol/5.0"));

So, in order to get cc as QMediaGaplessPlaybackControl change:

auto cc = service->requestControl("org.qt-project.qt.mediagaplessplaybackcontrol/5.0");

to:

auto *cc = static_cast<QMediaGaplessPlaybackControl *>(qobject_cast<QMediaControl  *>(service->requestControl("org.qt-project.qt.mediaplayercontrol/5.0")));

edited Sep 08 '18 at 13:50

answered Sep 08 '18 at 09:38

scopchanov

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You're right, but i need the QMediaGaplessPlaybackControl. Simply requesting "mediaplayercontrol" returns DirectShowPlayerControl – Fred Sep 08 '18 at 10:59
@Fred, I would advice you to post an example with enough details to reproduce the problem. – scopchanov Sep 08 '18 at 11:02
@Fred, you could also try to substitute `qobject_cast` with `qobject_cast`. – scopchanov Sep 08 '18 at 11:24
Updated my original post with the link, and the exact code. Thanks for the suggestions – Fred Sep 08 '18 at 12:31
Thanks, it works. :) Although doesn't support gapless playback :/ – Fred Sep 08 '18 at 17:49
@Fred, what do you mean by _doesn't support gapless playback_? Btw, if you like the answer, you might as well consider upvoting it. – scopchanov Sep 08 '18 at 19:26
I meant that calling QMediaGaplessPlaybackControl::isCrossfadeSupported returns false, and setting a crossfade interval has no effect. – Fred Sep 10 '18 at 10:10
@Fred, now I understand and that is indeed unfortunate. Also thank you for upvoting! – scopchanov Sep 10 '18 at 10:15
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Thanks for the help. :) – Fred Sep 10 '18 at 10:20

Why does QMediaGaplessPlaybackControl not exist?

1 Answers1