main.cpp

#include "pipeline.h"
#include <QApplication>
#include <QQmlApplicationEngine>
#include <QQuickWindow>
#include <QQuickItem>
#include <QRunnable>
#include <gst/gst.h>

int main(int argc, char *argv[])
{
  int ret;

  gst_init (&argc, &argv);

  {
    QGuiApplication app(argc, argv);

    qmlRegisterType<QPipeline>("Pipeline", 1, 0, "Pipeline");

    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

    ret = app.exec();
  }

  gst_deinit ();

  return ret;
}

pipeline.cpp

#include "pipeline.h"
#include <QPainter>

QPipeline::QPipeline(QQuickItem *parent)
    : QQuickPaintedItem(parent)
{
}

QVariant QPipeline::video() const
{
    return m_video;
}

void QPipeline::setVideo(const QVariant &video)
{
    m_video = video;

    if (m_pipe) {
      linkPipeToVideo();
    }
}

QString QPipeline::pipe() const
{
    return m_pipe;
}

void QPipeline::setPipe(const QString &pipe)
{
    m_pipe = pipe;
    pipeline = gst_parse_bin_from_description(pipe);

    if (m_video) {
      linkPipeToVideo();
    }
}

void QPipeline::linkPipeToVideo()
{
    GstElement *sink = gst_bin_get_by_name(m_pipe, "sink");
    QQuickItem *item = qvariant_cast<QQuickItem*>(m_video);

    g_object_set(sink, "widget", item, NULL);
}

void QPipeline::play()
{
  gst_element_set_state (pipeline, GST_STATE_PLAYING);
  emit playing();
}

void QPipeline::pause()
{
  gst_element_set_state (pipeline, GST_STATE_PAUSED);
  emit paused();
}

void QPipeline::paint(QPainter *painter)
{
}

pipeline.h

#include <QtQuick/QQuickPaintedItem>
#include <QColor>
#include <gst/gst.h>

class QPipeline : public QQuickPaintedItem
{
    Q_OBJECT
    Q_PROPERTY(QVariant video READ video WRITE setVideo)
    Q_PROPERTY(QString pipe READ pipe WRITE setPipe)

public:
    QPipeline(QQuickItem *parent = 0);

    QVariant video() const;
    void setVideo(const QVariant &video);

    QString pipe() const;
    void setPipe(const QString &pipe);

    void paint(QPainter *painter);

    Q_INVOKABLE void pause();
    Q_INVOKABLE void play();

signals:
    void playing();
    void paused();

private:
    QVariant m_video;
    QString m_pipe;

    GstElement pipeline;
    void linkPipeToVideo();
};