QVideoSink::videoFrameChanged not fired when dragging application window

[Nils Petter Skalerud]

This sounds like a bug to me. We'd need more information about your environment, platform and Qt version in order to investigate. Could you please file a bug report at the following bug tracker? https://bugreports.qt.io/

Please include information such include information such as:

• Platform (WIndows, Linux, Android...)
• Qt version
• Qt Multimedia media backend being used (FFmpeg, gstreamer, native)
• If it's a mobile or embedded device, please also include the model description.

[BrianL]

@Nils-Petter-Skalerud It seems like I am not authorized to create a bug, it asked me to log in but I was already logged in.

But here are the requested information:

• Platform: Windows
• Qt Version: 6.10.0
• Qt Multimedia media backend: I'm unsure about this one, is there somewhere I can check this?

[jsulm]

@BrianL said in QVideoSink::videoFrameChanged not fired when dragging application window:

Qt Multimedia media backend: I'm unsure about this one, is there somewhere I can check this?

You can set QT_DEBUG_PLUGINS env variable before starting your app and see which plug-ins are loaded.

[BrianL]

@jsulm

qt.core.plugin.factoryloader: checking directory path "C:/Qt6/6.10.0/mingw_64/plugins/multimedia" ...
qt.core.plugin.factoryloader: looking at "ffmpegmediaplugin.dll"
qt.core.plugin.loader: Found metadata in lib C:/Qt6/6.10.0/mingw_64/plugins/multimedia/ffmpegmediaplugin.dll, metadata=
{
    "IID": "org.qt-project.Qt.QPlatformMediaPlugin",
    "MetaData": {
        "Keys": [
            "ffmpeg"
        ]
    },
    "archlevel": 2,
    "className": "QFFmpegMediaPlugin",
    "debug": false,
    "version": 395776
}

[BrianL]

Update: it only starts lagging if the camera frame is big enough then it will lag when I drag the window, if I make the window smaller it doesn't lag

[jsulm]

@BrianL said in QVideoSink::videoFrameChanged not fired when dragging application window:

C:/Qt6/6.10.0/mingw_64/plugins/multimedia/ffmpegmediaplugin.dll

You're using ffmpeg backend

[BrianL]

Update on this: I have since switched to using LibVLC but the issue persist, so the issue seems to be in general if you are drawing something continuously over a certain size, dragging the window completely blocks the GUI thread.

[JoeCFD]

@BrianL Can you try to stop/pause the video before you drag and then resume the video after drag is finished? Qt5 Multimedia module does not work well with streaming. Not sure if Qt 6 has improved a lot.

[BrianL]

@JoeCFD Not really, the stream has to be continuous because I am doing image processing every frame in real time (the processing isn't affected since it's running on a different thread). I am using Qt6 as well

[JoeCFD]

@BrianL You can use gstreamer/FFmpeg pipeline + qml sink for rendering the stream. And the pipeline can be paused/stopped and restarted. Multimedia module in Qt5 is not great at rendering audio/video streaming. This module has been rewritten in Qt6. I am not sure if it is good enough now. I use gstreamer + qml sink for audio/video streaming.