Qt 6.4.3 QMediaPlayer::Resource Error "Could not open file"

Question

My organisation is using Qt 6.4.3 and using the Qt Multimedia(Widgets) module. Currently, I am unable to play any non-local files (http/https/rtsp/...) using the FFmpeg backend.

I have verified that the FFmpeg plugin loads with environment variable QT_DEBUG_PLUGINS=1.

Here is the system environment:

Qt Version      : 6.4.3
Operating System: Windows 10
Build tool      : Visual Studio 2022 (MSBuild)
QT_MEDIA_BACKEND: "ffmpeg"

I've seen a lot of examples of issues similar to mine, but with no satisfactory solution:

Qt Forums:

• https://forum.qt.io/topic/145002/issues-with-using-qt-multimedia-with-ffmpeg-in-qt-6-5-audio-streaming-on-macos/7
• https://forum.qt.io/topic/135819/showing-video-from-a-rtsp-ip-camera
• https://forum.qt.io/topic/115988/qmedia-player-not-working

Stack Overflow:

• QMediaPlayer resource error
• Cant load music file with QMediaPlayer
• https://stackoverflow.com/search?q=QMediaPlayer+resource+error

Here is a minimum reproducible example:

// qt headers [omitted]

int main(int argc, char* argv[]) {
    // Set environment variables (also in Windows Environment Variables)
    qputenv("QT_MEDIA_BACKEND", "ffmpeg");

    QApplication a(argc, argv);

    std::array<QUrl, 2> testUrls = {{
        // Local file works:
        QUrl::fromUserInput(R"(C:\<Replace With Your Own Local MP4 file>)"),
        // Remote URL fails in Qt, but loads in ffplay and vlc:
        QUrl::fromUserInput("http://vjs.zencdn.net/v/oceans.mp4"),
    }};

    QComboBox *urlSelection = new QComboBox();
    for (QUrl testUrl : testUrls)
    {
        urlSelection->addItem(testUrl.toString(), testUrl);
    }

    QPushButton *playButton = new QPushButton();
    playButton->setText("PLAY");

    QVideoWidget *videoWidget = new QVideoWidget();
    videoWidget->setFixedSize(QSize(854, 480));

    QAudioOutput *audioOutput = new QAudioOutput();
    QMediaPlayer *mediaPlayer = new QMediaPlayer();

    QObject::connect(playButton, &QPushButton::clicked, [=](bool) {
        QUrl url = urlSelection->currentData().toUrl();
        mediaPlayer->setSource(url);
        mediaPlayer->setVideoOutput(videoWidget);
        mediaPlayer->setAudioOutput(audioOutput);
        mediaPlayer->play();
    });

    QWidget *widget = new QWidget();
    widget->setLayout(new QVBoxLayout());
    widget->layout()->addWidget(videoWidget);
    widget->layout()->addWidget(urlSelection);
    widget->layout()->addWidget(playButton);

    QMainWindow *mainWindow = new QMainWindow();
    mainWindow->setCentralWidget(widget);
    mainWindow->show();

    return a.exec();
}

The debug console produces the following log when accessing the remote url specified:

[ DEBUG: Player Status ] QMediaPlayer::LoadingMedia
[ DEBUG: Player Error ] QMediaPlayer::ResourceError "Could not open file"
[ DEBUG: Player Playback ] QMediaPlayer::PlayingState
[ DEBUG: Player Status ] QMediaPlayer::BufferedMedia
[ DEBUG: Player Status ] QMediaPlayer::LoadedMedia

Answer 1

From QTBUG-110708 and QTBUG-11910, it appears that this bug is specific to prior versions of Qt (6.5.0 and earlier).

It was fixed in Qt 6.5.1; the problem vanishes after upgrading to it, meaning it's possible to play videos from the provided URL while using FFmpeg.

For more:

• Qt Forum: https protocol not found, recompile FFmpeg with openssl, gnutls or securetransport enabled.