I have a question about accessing libmpv properties in Qt

[CodeFarmer]

Problem descriptionL：

"I've been working on a small project, creating a demo for a video player. I'm trying to access the frame rate of the currently playing video using mpv_observe_property(mpv, 0, "estimated-vf-fps", MPV_FORMAT_DOUBLE);. It works fine in the callback mpv_events and I can retrieve the frame rate. However, the issue arises when I also try to observe the video time information using mpv_observe_property(mpv, 0, "time-pos", MPV_FORMAT_DOUBLE); during program initialization. This seems to cause the program to crash. It appears that I can only observe one property at a time when the mpv object is created. How can I solve this problem?"

Below is the relevant code snippet:

void MpvPlayer::create_mvpPlayer(QWidget *videoWin)
{
    // create mpv instance
    mpv = mpv_create();
    if (!mpv)
        throw std::runtime_error("can't create mpv instance");

    int64_t wid = videoWin->winId();

    mpv_set_option(mpv, "wid", MPV_FORMAT_INT64, &wid);

    mpv_observe_property(mpv, 0, "time-pos", MPV_FORMAT_DOUBLE);

    //mpv_observe_property(mpv, 0, "estimated-vf-fps", MPV_FORMAT_DOUBLE);


    


connect(this, &MpvPlayer::mpv_events, this, &MpvPlayer::on_mpv_events,
            Qt::QueuedConnection);
    
    

    mpv_set_wakeup_callback(mpv, wakeup, this);

    
    if (mpv_initialize(mpv) < 0)
        throw std::runtime_error("mpv to initialize failed ！");
}

void MpvPlayer::on_mpv_events()
{
    // All events are processed until the event queue is empty
    while (mpv)
    {
        mpv_event *event = mpv_wait_event(mpv, 0);
        if (event->event_id == MPV_EVENT_NONE)
            break;
        handle_mpv_event(event);
    }
}
void MpvPlayer::handle_mpv_event(mpv_event *event)
{
    switch (event->event_id)
    {
        
        case MPV_EVENT_PROPERTY_CHANGE:
        {
            mpv_event_property *prop = (mpv_event_property *)event->data;

            if (strcmp(prop->name, "time-pos") == 0)
            {
                if (prop->format == MPV_FORMAT_DOUBLE)
                {
                    
                    double time = *(double *)prop->data;

                    //qDebug() << "time: " << QString::number(time, 10, 2);
                    //qDebug() << prop->name << prop->format << prop->data;
                   // qDebug() << getProperty("time-pos");
                    //qDebug() <<getProperty("playback-time");
                    //qDebug()<<getProperty("duration");
                    double totalTime = getProperty("duration").toDouble();
                    double passTime = time;
                    emit mpv_sendTimeInformat(totalTime,passTime);


                }
                else if (prop->format == MPV_FORMAT_NONE)
                {
                    
                    emit mpv_palyEnd();
                    qDebug() << "End of playback";
                }
            } else if(strcmp(prop->name, "estimated-vf-fps") == 0) {
                
                double estimated_fps = *(double *)prop->data;
                emit fpsChanged(estimated_fps);
            }

        }
        break;

        // palyer Exit event triggering
        case MPV_EVENT_SHUTDOWN:
        {
            mpv_terminate_destroy(mpv);
            mpv = NULL;
        }
        break;

        default: ;
    }
}

[SGaist]

Hi and welcome to devnet,

Are you using this example as a base ?

[CodeFarmer]

@SGaist
Yeah, I checked out an example. It's basically built upon the example provided by the official mpv. So, you can say what I wrote is kind of based on that.

[trin94]

@CodeFarmer There's a library in the KDE landscape that you can have a look at :)

https://invent.kde.org/libraries/mpvqt

[CodeFarmer]

@trin94 Thanks for getting back to me and for all your help