Video: Replace OpenGL qml6glsink with appsink Metal path on macOS

On macOS, the GStreamer qml6glsink element requires an OpenGL context,
but Qt 6 defaults to Metal RHI. Rather than forcing OpenGL (deprecated
on macOS), this adds a new appsink-based rendering path:

  GStreamer pipeline -> appsink -> GstAppSinkAdapter -> QVideoSink -> VideoOutput (Metal)

Changes:
- gstqgcvideosinkbin: Add macOS appsink path (videoconvert -> appsink)
  alongside existing D3D11 (Windows) and GL (Linux) paths
- GstAppSinkAdapter: New class bridging GStreamer appsink to Qt QVideoSink,
  copies BGRA frames with stride-aware memcpy and buffer bounds validation
- FlightDisplayViewMetal.qml: Qt VideoOutput component for Metal rendering
- FlightDisplayViewVideo.qml: 3-way component selection (D3D11/Metal/GL)
  for both main and thermal video
- QGCApplication: Let Qt use default Metal RHI on macOS instead of
  forcing OpenGL
- VideoManager: Expose gstreamerAppleSink property, wire appsink adapter
  to QML VideoOutput's QVideoSink
- GStreamer CMakeLists: Add GstApp dependency, Apple-gated sources and
  Qt Multimedia links
- Unit test: _testAppsinkFrameDelivery validates end-to-end frame delivery
  through the appsink pipeline (macOS-only, QSKIP elsewhere)

All changes are gated behind Q_OS_MACOS / if(APPLE) -- no impact on
Windows, Linux, Android, or iOS builds.

Author: DonLakeFlyer

src/FlyView/CMakeLists.txt

@@ -16,6 +16,7 @@ qt_add_qml_module(FlyViewModule
         FlightDisplayViewDummy.qml
         FlightDisplayViewGStreamer.qml
         FlightDisplayViewGStreamerD3D11.qml
+        FlightDisplayViewMetal.qml
         FlightDisplayViewQtMultimedia.qml
         FlightDisplayViewUVC.qml
         FlightDisplayViewVideo.qml

src/FlyView/FlightDisplayViewMetal.qml

@@ -0,0 +1,22 @@
+import QtQuick
+import QtMultimedia
+
+import QGroundControl
+
+// macOS Metal rendering path for GStreamer video.
+// Frames are pushed from the C++ GstAppSinkAdapter to this VideoOutput's QVideoSink.
+VideoOutput {
+    objectName: "videoContent"
+    fillMode:   VideoOutput.PreserveAspectFit
+
+    Connections {
+        target: QGroundControl.videoManager
+        function onImageFileChanged(filename) {
+            grabToImage(function(result) {
+                if (!result.saveToFile(filename)) {
+                    console.error('Error capturing video frame');
+                }
+            });
+        }
+    }
+}

src/FlyView/FlightDisplayViewVideo.qml

@@ -137,6 +137,11 @@ Item {
                 }
             }
         }
+        Component {
+            id: videoBackgroundMetalComponent
+            FlightDisplayViewMetal {
+            }
+        }
         Loader {
             // GStreamer is causing crashes on Lenovo laptop OpenGL Intel drivers. In order to workaround this
             // we don't load a QGCVideoBackground object when video is disabled. This prevents any video rendering
@@ -146,7 +151,9 @@ Item {
             visible:            _showStreamLoader
             sourceComponent:    QGroundControl.videoManager.gstreamerD3D11Sink
                                     ? videoBackgroundD3D11Component
-                                    : videoBackgroundGLComponent
+                                    : QGroundControl.videoManager.gstreamerAppleSink
+                                        ? videoBackgroundMetalComponent
+                                        : videoBackgroundGLComponent
 
             property bool videoDisabled: QGroundControl.settingsManager.videoSettings.videoSource.rawValue === QGroundControl.settingsManager.videoSettings.disabledVideoSource
         }
@@ -233,7 +240,10 @@ Item {
                 anchors.fill:   parent
                 opacity:        _camera ? (_camera.thermalMode === MavlinkCameraControlInterface.THERMAL_BLEND ? _camera.thermalOpacity / 100 : 1.0) : 0
                 sourceComponent: QGroundControl.videoManager.gstreamerD3D11Sink
-                    ? thermalBackgroundD3D11 : thermalBackgroundGL
+                    ? thermalBackgroundD3D11
+                    : QGroundControl.videoManager.gstreamerAppleSink
+                        ? thermalBackgroundMetal
+                        : thermalBackgroundGL
                 onLoaded: { if (item) item.objectName = "thermalVideo" }
 
                 Component {
@@ -244,6 +254,10 @@ Item {
                     id: thermalBackgroundD3D11
                     QGCVideoBackgroundD3D11 {}
                 }
+                Component {
+                    id: thermalBackgroundMetal
+                    FlightDisplayViewMetal {}
+                }
             }
         }
         //-- Zoom

src/QGCApplication.cc

@@ -255,15 +255,17 @@ bool QGCApplication::_initVideo()
         QQuickWindow::setGraphicsApi(QSGRendererInterface::OpenGL);
     }
     qCDebug(QGCApplicationLog) << "D3D11 video sink available, using default graphics API";
+#elif defined(Q_OS_MACOS)
+    // macOS Metal rendering path: appsink → QVideoSink → VideoOutput.
+    // Do NOT force OpenGL — let Qt use the default Metal RHI backend.
+    // The appsink path in qgcvideosinkbin avoids the GL-dependent qml6glsink.
+    if (isOffscreen) {
+        QQuickWindow::setGraphicsApi(QSGRendererInterface::OpenGL);
+    } else {
+        qCDebug(QGCApplicationLog) << "macOS: using default RHI backend (Metal) for appsink video path";
+    }
 #else
-    const bool skipGLProbe = isOffscreen
-#if defined(Q_OS_MACOS)
-        // macOS still provides OpenGL (deprecated but functional). The
-        // QOpenGLContext::create() probe is unreliable without a native
-        // surface, so skip it and force OpenGL for qml6glsink.
-        || true
-#endif
-        ;
+    const bool skipGLProbe = isOffscreen;
 
     if (skipGLProbe) {
         QQuickWindow::setGraphicsApi(QSGRendererInterface::OpenGL);
@@ -276,7 +278,7 @@ bool QGCApplication::_initVideo()
                                          << "Using default graphics API (Metal/Vulkan).";
         }
     }
-#endif  // QGC_GST_D3D11_SINK
+#endif  // QGC_GST_D3D11_SINK / Q_OS_MACOS
 #endif
 
     QGCCorePlugin::instance();  // CorePlugin must be initialized before VideoManager for Video Cleanup

src/VideoManager/VideoManager.cc

@@ -22,6 +22,11 @@
 #include "UVCReceiver.h"
 #ifdef QGC_GST_STREAMING
 #include "GStreamerHelpers.h"
+#include "GStreamer.h"
+#endif
+#if defined(QGC_GST_STREAMING) && defined(Q_OS_MACOS)
+#include <QtMultimedia/QVideoSink>
+#include <QtMultimediaQuick/private/qquickvideooutput_p.h>
 #endif
 
 #include <QtConcurrent/QtConcurrent>
@@ -501,6 +506,15 @@ bool VideoManager::gstreamerD3D11Sink()
 #endif
 }
 
+bool VideoManager::gstreamerAppleSink()
+{
+#if defined(QGC_GST_STREAMING) && defined(Q_OS_MACOS) && !defined(QGC_GST_D3D11_SINK)
+    return true;
+#else
+    return false;
+#endif
+}
+
 bool VideoManager::uvcEnabled()
 {
     return UVCReceiver::enabled();
@@ -888,6 +902,22 @@ void VideoManager::_initVideoReceiver(VideoReceiver *receiver, QQuickWindow *win
     }
     receiver->setSink(sink);
 
+#if defined(QGC_GST_STREAMING) && defined(Q_OS_MACOS) && !defined(QGC_GST_D3D11_SINK)
+    // macOS Metal path: connect appsink inside the sinkbin to the QVideoSink
+    // belonging to the QML VideoOutput widget.
+    if (sink && widget) {
+        auto *videoOutput = qobject_cast<QQuickVideoOutput *>(widget);
+        if (videoOutput) {
+            QVideoSink *videoSink = videoOutput->videoSink();
+            if (!GStreamer::setupAppleSinkAdapter(sink, videoSink, receiver)) {
+                qCWarning(VideoManagerLog) << "setupAppleSinkAdapter failed" << receiver->name();
+            }
+        } else {
+            qCWarning(VideoManagerLog) << "Widget is not a VideoOutput, cannot connect appsink" << receiver->name();
+        }
+    }
+#endif
+
     (void) connect(receiver, &VideoReceiver::onStartComplete, this, [this, receiver](VideoReceiver::STATUS status) {
         qCDebug(VideoManagerLog) << "Video" << receiver->name() << "Start complete, status:" << status;
         switch (status) {

src/VideoManager/VideoManager.h

@@ -27,6 +27,7 @@ class VideoManager : public QObject
 
     Q_PROPERTY(bool     gstreamerEnabled        READ gstreamerEnabled                           CONSTANT)
     Q_PROPERTY(bool     gstreamerD3D11Sink      READ gstreamerD3D11Sink                         CONSTANT)
+    Q_PROPERTY(bool     gstreamerAppleSink      READ gstreamerAppleSink                         CONSTANT)
     Q_PROPERTY(bool     qtmultimediaEnabled     READ qtmultimediaEnabled                        CONSTANT)
     Q_PROPERTY(bool     uvcEnabled              READ uvcEnabled                                 CONSTANT)
     Q_PROPERTY(bool     autoStreamConfigured    READ autoStreamConfigured                       NOTIFY autoStreamConfiguredChanged)
@@ -83,6 +84,7 @@ class VideoManager : public QObject
     void setfullScreen(bool on);
     static bool gstreamerEnabled();
     static bool gstreamerD3D11Sink();
+    static bool gstreamerAppleSink();
     static bool qtmultimediaEnabled();
     static bool uvcEnabled();
 

src/VideoManager/VideoReceiver/GStreamer/CMakeLists.txt

@@ -4,7 +4,7 @@ target_sources(${CMAKE_PROJECT_NAME} PRIVATE VideoItemStub.h)
 if(QGC_ENABLE_GST_VIDEOSTREAMING)
     find_package(QGCGStreamer
         REQUIRED
-        COMPONENTS Core Base Video Gl GlPrototypes Rtsp
+        COMPONENTS Core Base Video Gl GlPrototypes Rtsp App
         OPTIONAL_COMPONENTS GlEgl GlWayland GlX11
     )
 
@@ -20,6 +20,19 @@ if(QGC_ENABLE_GST_VIDEOSTREAMING)
             GstVideoReceiver.h
     )
 
+    if(APPLE)
+        target_sources(${CMAKE_PROJECT_NAME}
+            PRIVATE
+                GstAppSinkAdapter.cc
+                GstAppSinkAdapter.h
+        )
+        target_link_libraries(${CMAKE_PROJECT_NAME}
+            PRIVATE
+                Qt6::Multimedia
+                Qt6::MultimediaQuickPrivate
+        )
+    endif()
+
     add_subdirectory(gstqgc)
 endif()
 

src/VideoManager/VideoReceiver/GStreamer/GStreamer.cc

@@ -4,6 +4,10 @@
 #include "AppSettings.h"
 #include "GstVideoReceiver.h"
 
+#ifdef Q_OS_MACOS
+#include "GstAppSinkAdapter.h"
+#endif
+
 #include <QtCore/QCoreApplication>
 #include <QtCore/QDir>
 #include <QtCore/QFileInfo>
@@ -870,4 +874,24 @@ VideoReceiver *createVideoReceiver(QObject *parent)
     return new GstVideoReceiver(parent);
 }
 
+bool setupAppleSinkAdapter(void *sinkBin, QVideoSink *videoSink, QObject *adapterParent)
+{
+#ifdef Q_OS_MACOS
+    if (!sinkBin || !videoSink) {
+        return false;
+    }
+
+    auto *adapter = new GstAppSinkAdapter(adapterParent);
+    if (!adapter->setup(GST_ELEMENT(sinkBin), videoSink)) {
+        qCCritical(GStreamerLog) << "GstAppSinkAdapter::setup() failed";
+        adapter->deleteLater();
+        return false;
+    }
+    return true;
+#else
+    Q_UNUSED(sinkBin); Q_UNUSED(videoSink); Q_UNUSED(adapterParent);
+    return false;
+#endif
+}
+
 } // namespace GStreamer

src/VideoManager/VideoReceiver/GStreamer/GStreamer.h

@@ -7,6 +7,7 @@ Q_DECLARE_LOGGING_CATEGORY(GStreamerAPILog)
 Q_DECLARE_LOGGING_CATEGORY(GStreamerDecoderRanksLog)
 
 class QQuickItem;
+class QVideoSink;
 class VideoReceiver;
 
 namespace GStreamer
@@ -31,4 +32,8 @@ void *createVideoSink(QQuickItem *widget, QObject *parent = nullptr);
 void releaseVideoSink(void *sink);
 VideoReceiver *createVideoReceiver(QObject *parent = nullptr);
 
+/// On macOS: connect the appsink inside the sinkbin to a QVideoSink.
+/// Returns true on success. No-op (returns false) on other platforms.
+bool setupAppleSinkAdapter(void *sinkBin, QVideoSink *videoSink, QObject *adapterParent);
+
 }