QT       += core gui multimedia  multimediawidgets

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>

#include <QMediaPlayer>
#include <QVideoWidget>
#include <QMediaPlaylist>

QT_BEGIN_NAMESPACE
namespace Ui { class Widget; }
QT_END_NAMESPACE

class Widget : public QWidget
{
    Q_OBJECT

public:
    Widget(QWidget *parent = nullptr);
    ~Widget();

private slots:
    void on_fileBtn_clicked();

private:
    Ui::Widget *ui;
    QMediaPlayer* mediaPlayer;
    QMediaPlaylist* mediaPlayList;
};
#endif // WIDGET_H

#include "widget.h"
#include "ui_widget.h"

#include <QFileDialog>

Widget::Widget(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::Widget)
{
    ui->setupUi(this);

    mediaPlayer = new QMediaPlayer(this);
    mediaPlayList = new QMediaPlaylist(mediaPlayer);
    mediaPlayer->setVideoOutput(ui->widget);
}

Widget::~Widget()
{
    delete ui;
}


void Widget::on_fileBtn_clicked()
{
    QString file = QFileDialog::getOpenFileName(this,"open file",".","*.*");
    if(file.isEmpty())
        return;

    mediaPlayList->clear();
    mediaPlayList->addMedia(QUrl::fromLocalFile(file));
    mediaPlayList->setCurrentIndex(0);
    mediaPlayer->setPlaylist(mediaPlayList);
    mediaPlayer->play();
}