Move gstreamer over to the new subtitle handling

Implement a custom sink for subtitles that notifies the video
sink about changes in the subtitles. Remove the subtitleoverlay
we have been using so far.

Change-Id: I6ecfb1ab8538169d7365f21e0c0648b4aa2cd769
Reviewed-by: Piotr Srebrny <piotr.srebrny@qt.io>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
(cherry picked from commit 8d5182d03c1967d77ca8da531b004e85bb0892f0)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

12 files changed, 379 insertions, 31 deletions

diff --git a/src/multimedia/CMakeLists.txt b/src/multimedia/CMakeLists.txt
index 13e166a93..b7d7a8b0d 100644
--- a/src/multimedia/CMakeLists.txt
+++ b/src/multimedia/CMakeLists.txt
@@ -212,6 +212,7 @@ qt_internal_extend_target(Multimedia CONDITION QT_FEATURE_gstreamer
         platform/gstreamer/common/qgstutils.cpp platform/gstreamer/common/qgstutils_p.h
         platform/gstreamer/common/qgstvideobuffer.cpp platform/gstreamer/common/qgstvideobuffer_p.h
         platform/gstreamer/common/qgstvideorenderersink.cpp platform/gstreamer/common/qgstvideorenderersink_p.h
+        platform/gstreamer/common/qgstsubtitlesink.cpp platform/gstreamer/common/qgstsubtitlesink_p.h
         platform/gstreamer/qgstreamermediadevices.cpp platform/gstreamer/qgstreamermediadevices_p.h
         platform/gstreamer/qgstreamerformatinfo.cpp platform/gstreamer/qgstreamerformatinfo_p.h
         platform/gstreamer/qgstreamerintegration.cpp platform/gstreamer/qgstreamerintegration_p.h
diff --git a/src/multimedia/platform/gstreamer/common/qgst_p.h b/src/multimedia/platform/gstreamer/common/qgst_p.h
index f0a0bf79d..12eb123c0 100644
--- a/src/multimedia/platform/gstreamer/common/qgst_p.h
+++ b/src/multimedia/platform/gstreamer/common/qgst_p.h
@@ -377,6 +377,9 @@ public:
 
     GstPad *pad() const { return GST_PAD_CAST(object()); }
 
+    GstEvent *stickyEvent(GstEventType type) { return gst_pad_get_sticky_event(pad(), type, 0); }
+    bool sendEvent(GstEvent *event) { return gst_pad_send_event (pad(), event); }
+
     template<auto Member, typename T>
     void addProbe(T *instance, GstPadProbeType type) {
         struct Impl {
diff --git a/src/multimedia/platform/gstreamer/common/qgstpipeline.cpp b/src/multimedia/platform/gstreamer/common/qgstpipeline.cpp
index ab2aa1c0e..3877694dd 100644
--- a/src/multimedia/platform/gstreamer/common/qgstpipeline.cpp
+++ b/src/multimedia/platform/gstreamer/common/qgstpipeline.cpp
@@ -66,6 +66,7 @@ public:
     mutable qint64 m_position = 0;
     double m_rate = 1.;
     bool m_flushOnConfigChanges = false;
+    bool m_pendingFlush = false;
 
     int m_configCounter = 0;
     GstState m_savedState = GST_STATE_NULL;
@@ -271,6 +272,16 @@ void QGstPipeline::removeMessageFilter(QGstreamerBusMessageFilter *filter)
     d->removeMessageFilter(filter);
 }
 
+GstStateChangeReturn QGstPipeline::setState(GstState state)
+{
+    auto retval = gst_element_set_state(element(), state);
+    if (d->m_pendingFlush) {
+        d->m_pendingFlush = false;
+        flush();
+    }
+    return retval;
+}
+
 void QGstPipeline::beginConfig()
 {
     if (!d)
@@ -296,8 +307,7 @@ void QGstPipeline::endConfig()
     if (d->m_configCounter)
         return;
 
-    if (d->m_savedState != GST_STATE_NULL && d->m_flushOnConfigChanges)
-        flush();
+    d->m_pendingFlush = true;
     if (d->m_savedState == GST_STATE_PLAYING)
         setState(GST_STATE_PLAYING);
     d->m_savedState = GST_STATE_NULL;
diff --git a/src/multimedia/platform/gstreamer/common/qgstpipeline_p.h b/src/multimedia/platform/gstreamer/common/qgstpipeline_p.h
index d5621c1b3..6ffaf33d6 100644
--- a/src/multimedia/platform/gstreamer/common/qgstpipeline_p.h
+++ b/src/multimedia/platform/gstreamer/common/qgstpipeline_p.h
@@ -100,6 +100,8 @@ public:
     void installMessageFilter(QGstreamerBusMessageFilter *filter);
     void removeMessageFilter(QGstreamerBusMessageFilter *filter);
 
+    GstStateChangeReturn setState(GstState state);
+
     GstPipeline *pipeline() const { return GST_PIPELINE_CAST(m_object); }
 
     void dumpGraph(const char *fileName)
diff --git a/src/multimedia/platform/gstreamer/common/qgstreamermediaplayer.cpp b/src/multimedia/platform/gstreamer/common/qgstreamermediaplayer.cpp
index 874b7bba1..f1aba4eda 100644
--- a/src/multimedia/platform/gstreamer/common/qgstreamermediaplayer.cpp
+++ b/src/multimedia/platform/gstreamer/common/qgstreamermediaplayer.cpp
@@ -78,6 +78,11 @@ QGstreamerMediaPlayer::QGstreamerMediaPlayer(QMediaPlayer *parent)
     inputSelector[AudioStream] = QGstElement("input-selector", "audioInputSelector");
     inputSelector[VideoStream] = QGstElement("input-selector", "videoInputSelector");
     inputSelector[SubtitleStream] = QGstElement("input-selector", "subTitleInputSelector");
+    for (int i = 0; i < 3; ++i)
+        inputSelector[i].set ("sync-streams", true);
+
+    inputSelector[SubtitleStream].set("sync-mode", 1 /*clock*/);
+    inputSelector[SubtitleStream].set("cache-buffers", true);
 
     playerPipeline.add(inputSelector[AudioStream], inputSelector[VideoStream], inputSelector[SubtitleStream]);
 
@@ -795,6 +800,10 @@ void QGstreamerMediaPlayer::setActiveTrack(QPlatformMediaPlayer::TrackType type,
     auto &selector = inputSelector[type];
     if (selector.isNull())
         return;
+
+    if (type == QPlatformMediaPlayer::SubtitleStream)
+        gstVideoOutput->flushSubtitles();
+
     selector.set("active-pad", streams.at(index));
     // seek to force an immediate change of the stream
     if (playerPipeline.state() == GST_STATE_PLAYING)
diff --git a/src/multimedia/platform/gstreamer/common/qgstreamermediaplayer_p.h b/src/multimedia/platform/gstreamer/common/qgstreamermediaplayer_p.h
index ca0139784..aba416498 100644
--- a/src/multimedia/platform/gstreamer/common/qgstreamermediaplayer_p.h
+++ b/src/multimedia/platform/gstreamer/common/qgstreamermediaplayer_p.h
@@ -115,6 +115,7 @@ public:
 
     bool processBusMessage(const QGstreamerMessage& message) override;
     bool processSyncMessage(const QGstreamerMessage& message) override;
+
 public Q_SLOTS:
     void updatePosition() { positionChanged(position()); }
 
diff --git a/src/multimedia/platform/gstreamer/common/qgstreamervideooutput.cpp b/src/multimedia/platform/gstreamer/common/qgstreamervideooutput.cpp
index 2cc4b38d8..36e0823d8 100644
--- a/src/multimedia/platform/gstreamer/common/qgstreamervideooutput.cpp
+++ b/src/multimedia/platform/gstreamer/common/qgstreamervideooutput.cpp
@@ -39,6 +39,7 @@
 
 #include <private/qgstreamervideooutput_p.h>
 #include <private/qgstreamervideosink_p.h>
+#include <private/qgstsubtitlesink_p.h>
 #include <qvideosink.h>
 
 #include <QtCore/qloggingcategory.h>
@@ -55,10 +56,8 @@ QGstreamerVideoOutput::QGstreamerVideoOutput(QObject *parent)
     videoQueue = QGstElement("queue", "videoQueue");
     videoConvert = QGstElement("videoconvert", "videoConvert");
     videoSink = QGstElement("fakesink", "fakeVideoSink");
-    subTitleQueue = QGstElement("queue", "subtitleQueue");
-    subtitleOverlay = QGstElement("subtitleoverlay", "subtitleoverlay");
-    gstVideoOutput.add(videoQueue, subtitleOverlay, videoConvert, videoSink, subTitleQueue);
-    if (!videoQueue.link(subtitleOverlay, videoConvert, videoSink))
+    gstVideoOutput.add(videoQueue, videoConvert, videoSink);
+    if (!videoQueue.link(videoConvert, videoSink))
         qCDebug(qLcMediaVideoOutput) << ">>>>>> linking failed";
 
     gstVideoOutput.addGhostPad(videoQueue, "sink");
@@ -72,19 +71,19 @@ QGstreamerVideoOutput::~QGstreamerVideoOutput()
 void QGstreamerVideoOutput::setVideoSink(QVideoSink *sink)
 {
     auto *gstVideoSink = sink ? static_cast<QGstreamerVideoSink *>(sink->platformVideoSink()) : nullptr;
-    if (gstVideoSink == m_videoWindow)
+    if (gstVideoSink == m_videoSink)
         return;
 
-    if (m_videoWindow)
-        m_videoWindow->setPipeline({});
+    if (m_videoSink)
+        m_videoSink->setPipeline({});
 
-    m_videoWindow = gstVideoSink;
-    if (m_videoWindow)
-        m_videoWindow->setPipeline(gstPipeline);
+    m_videoSink = gstVideoSink;
+    if (m_videoSink)
+        m_videoSink->setPipeline(gstPipeline);
 
     QGstElement gstSink;
-    if (m_videoWindow) {
-        gstSink = m_videoWindow->gstSink();
+    if (m_videoSink) {
+        gstSink = m_videoSink->gstSink();
         isFakeSink = false;
     } else {
         gstSink = QGstElement("fakesink", "fakevideosink");
@@ -107,6 +106,8 @@ void QGstreamerVideoOutput::setVideoSink(QVideoSink *sink)
     gst_element_send_event(videoSink.element(), event);
     videoSink.setState(GST_STATE_PAUSED);
 
+    doLinkSubtitleStream();
+
     gstPipeline.endConfig();
 
     qCDebug(qLcMediaVideoOutput) << "sinkChanged" << gstSink.name();
@@ -121,8 +122,8 @@ void QGstreamerVideoOutput::setVideoSink(QVideoSink *sink)
 void QGstreamerVideoOutput::setPipeline(const QGstPipeline &pipeline)
 {
     gstPipeline = pipeline;
-    if (m_videoWindow)
-        m_videoWindow->setPipeline(gstPipeline);
+    if (m_videoSink)
+        m_videoSink->setPipeline(gstPipeline);
 }
 
 void QGstreamerVideoOutput::linkSubtitleStream(QGstElement src)
@@ -132,20 +133,26 @@ void QGstreamerVideoOutput::linkSubtitleStream(QGstElement src)
         return;
 
     gstPipeline.beginConfig();
+    subtitleSrc = src;
+    doLinkSubtitleStream();
+    gstPipeline.endConfig();
+}
 
-    if (!subtitleSrc.isNull()) {
-        subtitleSrc.unlink(subTitleQueue);
-        subTitleQueue.unlink(subtitleOverlay);
+void QGstreamerVideoOutput::doLinkSubtitleStream()
+{
+    if (!subtitleSink.isNull()) {
+        subtitleSink.setStateSync(GST_STATE_NULL);
+        gstPipeline.remove(subtitleSink);
+        subtitleSink = {};
     }
-    subtitleSrc = src;
-    if (!subtitleSrc.isNull()) {
-        if (!subtitleSrc.link(subTitleQueue))
-            qCDebug(qLcMediaVideoOutput) << "link subtitle stream 1 failed";
-        if (!subTitleQueue.link(subtitleOverlay))
-            qCDebug(qLcMediaVideoOutput) << "link subtitle stream 1 failed";
+    if (!m_videoSink || subtitleSrc.isNull())
+        return;
+    if (subtitleSink.isNull()) {
+        subtitleSink = m_videoSink->subtitleSink();
+        gstPipeline.add(subtitleSink);
     }
-
-    gstPipeline.endConfig();
+    if (!subtitleSrc.link(subtitleSink))
+        qCDebug(qLcMediaVideoOutput) << "link subtitle stream failed";
 }
 
 void QGstreamerVideoOutput::setIsPreview()
@@ -159,4 +166,15 @@ void QGstreamerVideoOutput::setIsPreview()
     videoQueue.set("max-size-time", 0);
 }
 
+void QGstreamerVideoOutput::flushSubtitles()
+{
+    if (!subtitleSink.isNull()) {
+        auto pad = subtitleSink.staticPad("sink");
+        auto *event = gst_event_new_flush_start();
+        pad.sendEvent(event);
+        event = gst_event_new_flush_stop(false);
+        pad.sendEvent(event);
+    }
+}
+
 QT_END_NAMESPACE
diff --git a/src/multimedia/platform/gstreamer/common/qgstreamervideooutput_p.h b/src/multimedia/platform/gstreamer/common/qgstreamervideooutput_p.h
index 1468343ab..41e8da413 100644
--- a/src/multimedia/platform/gstreamer/common/qgstreamervideooutput_p.h
+++ b/src/multimedia/platform/gstreamer/common/qgstreamervideooutput_p.h
@@ -73,7 +73,7 @@ public:
     ~QGstreamerVideoOutput();
 
     void setVideoSink(QVideoSink *sink);
-    QGstreamerVideoSink *gstreamerVideoSink() const { return m_videoWindow; }
+    QGstreamerVideoSink *gstreamerVideoSink() const { return m_videoSink; }
 
     void setPipeline(const QGstPipeline &pipeline);
 
@@ -81,23 +81,24 @@ public:
     void linkSubtitleStream(QGstElement subtitleSrc);
 
     void setIsPreview();
+    void flushSubtitles();
 
 private:
+    void doLinkSubtitleStream();
 
-    QPointer<QGstreamerVideoSink> m_videoWindow;
+    QPointer<QGstreamerVideoSink> m_videoSink;
     bool isFakeSink = true;
 
     // Gst elements
     QGstPipeline gstPipeline;
 
     QGstBin gstVideoOutput;
-    QGstElement subTitleQueue;
     QGstElement videoQueue;
     QGstElement videoConvert;
-    QGstElement subtitleOverlay;
     QGstElement videoSink;
 
     QGstElement subtitleSrc;
+    QGstElement subtitleSink;
 };
 
 QT_END_NAMESPACE
diff --git a/src/multimedia/platform/gstreamer/common/qgstreamervideosink.cpp b/src/multimedia/platform/gstreamer/common/qgstreamervideosink.cpp
index a770d0e57..ca7daf6eb 100644
--- a/src/multimedia/platform/gstreamer/common/qgstreamervideosink.cpp
+++ b/src/multimedia/platform/gstreamer/common/qgstreamervideosink.cpp
@@ -39,6 +39,7 @@
 
 #include "qgstreamervideosink_p.h"
 #include "private/qgstvideorenderersink_p.h"
+#include "private/qgstsubtitlesink_p.h"
 #include <private/qgstutils_p.h>
 #include <QtGui/private/qrhi_p.h>
 
@@ -91,6 +92,8 @@ QGstreamerVideoSink::QGstreamerVideoSink(QVideoSink *parent)
     sinkBin.add(gstQueue, gstPreprocess);
     gstQueue.link(gstPreprocess);
     sinkBin.addGhostPad(gstQueue, "sink");
+
+    gstSubtitleSink = GST_ELEMENT(QGstSubtitleSink::createSink(this));
 }
 
 QGstreamerVideoSink::~QGstreamerVideoSink()
diff --git a/src/multimedia/platform/gstreamer/common/qgstreamervideosink_p.h b/src/multimedia/platform/gstreamer/common/qgstreamervideosink_p.h
index e6d588a36..a049bc465 100644
--- a/src/multimedia/platform/gstreamer/common/qgstreamervideosink_p.h
+++ b/src/multimedia/platform/gstreamer/common/qgstreamervideosink_p.h
@@ -79,6 +79,7 @@ public:
     QRhi *rhi() const { return m_rhi; }
 
     QGstElement gstSink();
+    QGstElement subtitleSink() const { return gstSubtitleSink; }
 
     void setPipeline(QGstPipeline pipeline);
 
@@ -100,6 +101,7 @@ private:
     QGstElement gstPreprocess;
     QGstElement gstVideoSink;
     QGstElement gstQtSink;
+    QGstElement gstSubtitleSink;
 
     QRhi *m_rhi = nullptr;
 
diff --git a/src/multimedia/platform/gstreamer/common/qgstsubtitlesink.cpp b/src/multimedia/platform/gstreamer/common/qgstsubtitlesink.cpp
new file mode 100644
index 000000000..d9b76d57f
--- /dev/null
+++ b/src/multimedia/platform/gstreamer/common/qgstsubtitlesink.cpp
@@ -0,0 +1,192 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 The Qt Company
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QDebug>
+#include <QThread>
+#include <QEvent>
+
+#include "qgstreamervideosink_p.h"
+#include "qgstsubtitlesink_p.h"
+#include "qgstutils_p.h"
+
+QT_BEGIN_NAMESPACE
+
+static GstBaseSinkClass *sink_parent_class;
+static thread_local QGstreamerVideoSink *current_sink;
+
+#define ST_SINK(s) QGstSubtitleSink *sink(reinterpret_cast<QGstSubtitleSink *>(s))
+
+QGstSubtitleSink *QGstSubtitleSink::createSink(QGstreamerVideoSink *sink)
+{
+    current_sink = sink;
+
+    QGstSubtitleSink *gstSink = reinterpret_cast<QGstSubtitleSink *>(
+            g_object_new(QGstSubtitleSink::get_type(), nullptr));
+    g_object_set(gstSink, "async", false, nullptr);
+
+    return gstSink;
+}
+
+GType QGstSubtitleSink::get_type()
+{
+    static GType type = 0;
+
+    if (type == 0) {
+        static const GTypeInfo info =
+        {
+            sizeof(QGstSubtitleSinkClass),                    // class_size
+            base_init,                                         // base_init
+            nullptr,                                           // base_finalize
+            class_init,                                        // class_init
+            nullptr,                                           // class_finalize
+            nullptr,                                           // class_data
+            sizeof(QGstSubtitleSink),                         // instance_size
+            0,                                                 // n_preallocs
+            instance_init,                                     // instance_init
+            nullptr                                                  // value_table
+        };
+
+        type = g_type_register_static(
+                GST_TYPE_BASE_SINK, "QGstSubtitleSink", &info, GTypeFlags(0));
+
+        // Register the sink type to be used in custom piplines.
+        // When surface is ready the sink can be used.
+        gst_element_register(nullptr, "qtsubtitlesink", GST_RANK_PRIMARY, type);
+    }
+
+    return type;
+}
+
+void QGstSubtitleSink::class_init(gpointer g_class, gpointer class_data)
+{
+    Q_UNUSED(class_data);
+
+    sink_parent_class = reinterpret_cast<GstBaseSinkClass *>(g_type_class_peek_parent(g_class));
+
+    GstBaseSinkClass *base_sink_class = reinterpret_cast<GstBaseSinkClass *>(g_class);
+    base_sink_class->render = QGstSubtitleSink::render;
+    base_sink_class->get_caps = QGstSubtitleSink::get_caps;
+    base_sink_class->set_caps = QGstSubtitleSink::set_caps;
+    base_sink_class->propose_allocation = QGstSubtitleSink::propose_allocation;
+    base_sink_class->wait_event = QGstSubtitleSink::wait_event;
+
+    GstElementClass *element_class = reinterpret_cast<GstElementClass *>(g_class);
+    element_class->change_state = QGstSubtitleSink::change_state;
+    gst_element_class_set_metadata(element_class,
+        "Qt built-in subtitle sink",
+        "Sink/Subtitle",
+        "Qt default built-in subtitle sink",
+        "The Qt Company");
+
+    GObjectClass *object_class = reinterpret_cast<GObjectClass *>(g_class);
+    object_class->finalize = QGstSubtitleSink::finalize;
+}
+
+void QGstSubtitleSink::base_init(gpointer g_class)
+{
+    static GstStaticPadTemplate sink_pad_template = GST_STATIC_PAD_TEMPLATE(
+            "sink", GST_PAD_SINK, GST_PAD_ALWAYS, GST_STATIC_CAPS("ANY"));
+
+    gst_element_class_add_pad_template(
+            GST_ELEMENT_CLASS(g_class), gst_static_pad_template_get(&sink_pad_template));
+}
+
+void QGstSubtitleSink::instance_init(GTypeInstance *instance, gpointer g_class)
+{
+    Q_UNUSED(g_class);
+    ST_SINK(instance);
+
+    Q_ASSERT(current_sink);
+    sink->sink = current_sink;
+    current_sink = nullptr;
+}
+
+void QGstSubtitleSink::finalize(GObject *object)
+{
+    // Chain up
+    G_OBJECT_CLASS(sink_parent_class)->finalize(object);
+}
+
+GstStateChangeReturn QGstSubtitleSink::change_state(GstElement *element, GstStateChange transition)
+{
+    return GST_ELEMENT_CLASS(sink_parent_class)->change_state(element, transition);
+}
+
+GstCaps *QGstSubtitleSink::get_caps(GstBaseSink *base, GstCaps *filter)
+{
+    return sink_parent_class->get_caps(base, filter);
+}
+
+gboolean QGstSubtitleSink::set_caps(GstBaseSink *base, GstCaps *caps)
+{
+    qDebug() << "set_caps:" << QGstCaps(caps).toString();
+    return sink_parent_class->set_caps(base, caps);
+}
+
+gboolean QGstSubtitleSink::propose_allocation(GstBaseSink *base, GstQuery *query)
+{
+    return sink_parent_class->propose_allocation(base, query);
+}
+
+GstFlowReturn QGstSubtitleSink::wait_event(GstBaseSink *base, GstEvent *event)
+{
+    GstFlowReturn retval = sink_parent_class->wait_event(base, event);
+    ST_SINK(base);
+    if (event->type == GST_EVENT_GAP) {
+//        qDebug() << "gap, clearing subtitle";
+        sink->sink->setSubtitleText(QString());
+    }
+    return retval;
+}
+
+GstFlowReturn QGstSubtitleSink::render(GstBaseSink *base, GstBuffer *buffer)
+{
+    ST_SINK(base);
+    GstMemory *mem = gst_buffer_get_memory(buffer, 0);
+    GstMapInfo info;
+    QString subtitle;
+    if (gst_memory_map(mem, &info, GST_MAP_READ))
+        subtitle = QString::fromUtf8(info.data);
+    gst_memory_unmap(mem, &info);
+//    qDebug() << "render" << buffer << subtitle;
+    sink->sink->setSubtitleText(subtitle);
+    return GST_FLOW_OK;
+}
+
+QT_END_NAMESPACE
diff --git a/src/multimedia/platform/gstreamer/common/qgstsubtitlesink_p.h b/src/multimedia/platform/gstreamer/common/qgstsubtitlesink_p.h
new file mode 100644
index 000000000..aa9127c7d
--- /dev/null
+++ b/src/multimedia/platform/gstreamer/common/qgstsubtitlesink_p.h
@@ -0,0 +1,106 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 The Qt Company
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QGSTSUBTITLESINK_P_H
+#define QGSTSUBTITLESINK_P_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API. It exists purely as an
+// implementation detail. This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#include <QtMultimedia/private/qtmultimediaglobal_p.h>
+
+#include <QtCore/qlist.h>
+#include <QtCore/qmutex.h>
+#include <QtCore/qqueue.h>
+#include <QtCore/qpointer.h>
+#include <QtCore/qwaitcondition.h>
+#include <private/qgst_p.h>
+#include <gst/base/gstbasesink.h>
+
+QT_BEGIN_NAMESPACE
+
+class QGstreamerVideoSink;
+
+class Q_MULTIMEDIA_EXPORT QGstSubtitleSink
+{
+public:
+    GstBaseSink parent;
+
+    static QGstSubtitleSink *createSink(QGstreamerVideoSink *sink);
+
+private:
+    static GType get_type();
+    static void class_init(gpointer g_class, gpointer class_data);
+    static void base_init(gpointer g_class);
+    static void instance_init(GTypeInstance *instance, gpointer g_class);
+
+    static void finalize(GObject *object);
+
+    static GstStateChangeReturn change_state(GstElement *element, GstStateChange transition);
+
+    static GstCaps *get_caps(GstBaseSink *sink, GstCaps *filter);
+    static gboolean set_caps(GstBaseSink *sink, GstCaps *caps);
+
+    static gboolean propose_allocation(GstBaseSink *sink, GstQuery *query);
+
+    static GstFlowReturn wait_event(GstBaseSink * sink, GstEvent * event);
+    static GstFlowReturn render(GstBaseSink *sink, GstBuffer *buffer);
+
+private:
+    QGstreamerVideoSink *sink = nullptr;
+};
+
+
+class QGstSubtitleSinkClass
+{
+public:
+    GstBaseSinkClass parent_class;
+};
+
+QT_END_NAMESPACE
+
+#endif