GStreamer: camera - prevent pipeline changes while pipeline is running

When switching cameras, `QGstreamerCamera::setCamera` would modify the
pipeline while it's running

Pick-to: 6.5
Change-Id: I96895b882270018f900126979f161ca614adfb16
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>
(cherry picked from commit d0e41971ea34dd802bb04159e1a7f49e50e4dac5)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 992812185cf2c207b75b2455c85327cac3475e51)

3 files changed, 37 insertions, 18 deletions

diff --git a/src/plugins/multimedia/gstreamer/mediacapture/qgstreamercamera.cpp b/src/plugins/multimedia/gstreamer/mediacapture/qgstreamercamera.cpp
index c1aaab818..226a08bc9 100644
--- a/src/plugins/multimedia/gstreamer/mediacapture/qgstreamercamera.cpp
+++ b/src/plugins/multimedia/gstreamer/mediacapture/qgstreamercamera.cpp
@@ -103,20 +103,22 @@ void QGstreamerCamera::setCamera(const QCameraDevice &camera)
     auto gstNewDecode = QGstElement::createFromFactory(
             f.pixelFormat() == QVideoFrameFormat::Format_Jpeg ? "jpegdec" : "identity");
 
-    qUnlinkGstElements(gstCamera, gstCapsFilter, gstDecode, gstVideoConvert);
-    gstCameraBin.stopAndRemoveElements(gstCamera, gstDecode);
-
-    gstCapsFilter.set("caps", caps);
+    auto updateCameraBin = [&] {
+        qUnlinkGstElements(gstCamera, gstCapsFilter, gstDecode, gstVideoConvert);
+        gstCameraBin.stopAndRemoveElements(gstCamera, gstDecode);
 
-    gstCameraBin.add(gstNewCamera, gstNewDecode);
-    qLinkGstElements(gstNewCamera, gstCapsFilter, gstNewDecode, gstVideoConvert);
+        gstCapsFilter.set("caps", caps);
 
-    // Start sending frames once pipeline is linked
-    // FIXME: put camera to READY state before linking to decoder as in the NULL state it does not
-    // know its true caps
+        gstCameraBin.add(gstNewCamera, gstNewDecode);
+        qLinkGstElements(gstNewCamera, gstCapsFilter, gstNewDecode, gstVideoConvert);
 
-    gstCameraBin.syncChildrenState();
+        gstCameraBin.syncChildrenState();
+    };
 
+    if (gstPipeline)
+        gstPipeline.modifyPipelineWhileNotRunning(updateCameraBin);
+    else
+        updateCameraBin();
 
     gstCamera = gstNewCamera;
     gstDecode = gstNewDecode;
@@ -137,23 +139,35 @@ bool QGstreamerCamera::setCameraFormat(const QCameraFormat &format)
 
     auto newGstDecode = QGstElement::createFromFactory(
             f.pixelFormat() == QVideoFrameFormat::Format_Jpeg ? "jpegdec" : "identity");
-    gstCameraBin.add(newGstDecode);
-    newGstDecode.syncStateWithParent();
 
-    gstCamera.staticPad("src").doInIdleProbe([&]() {
+    auto updateCameraBin = [&] {
+        newGstDecode.syncStateWithParent();
+
         qUnlinkGstElements(gstCamera, gstCapsFilter, gstDecode, gstVideoConvert);
+        gstCameraBin.stopAndRemoveElements(gstDecode);
 
         gstCapsFilter.set("caps", caps);
+
+        gstCameraBin.add(newGstDecode);
         qLinkGstElements(gstCamera, gstCapsFilter, newGstDecode, gstVideoConvert);
-    });
+        gstCameraBin.syncChildrenState();
+    };
 
-    gstCameraBin.stopAndRemoveElements(gstDecode);
+    if (gstPipeline)
+        gstPipeline.modifyPipelineWhileNotRunning(updateCameraBin);
+    else
+        updateCameraBin();
 
     gstDecode = newGstDecode;
 
     return true;
 }
 
+void QGstreamerCamera::setPipeline(QGstPipeline const &pipeline)
+{
+    gstPipeline = pipeline;
+}
+
 void QGstreamerCamera::updateCameraProperties()
 {
 #if QT_CONFIG(linux_v4l)
diff --git a/src/plugins/multimedia/gstreamer/mediacapture/qgstreamercamera_p.h b/src/plugins/multimedia/gstreamer/mediacapture/qgstreamercamera_p.h
index 7926f9004..59d69337f 100644
--- a/src/plugins/multimedia/gstreamer/mediacapture/qgstreamercamera_p.h
+++ b/src/plugins/multimedia/gstreamer/mediacapture/qgstreamercamera_p.h
@@ -15,11 +15,12 @@
 // We mean it.
 //
 
-#include <QHash>
 #include <private/qplatformcamera_p.h>
 #include <private/qmultimediautils_p.h>
-#include "qgstreamermediacapture_p.h"
-#include <qgst_p.h>
+
+#include <mediacapture/qgstreamermediacapture_p.h>
+#include <common/qgst_p.h>
+#include <common/qgstpipeline_p.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -37,6 +38,7 @@ public:
     void setCamera(const QCameraDevice &camera) override;
     bool setCameraFormat(const QCameraFormat &format) override;
 
+    void setPipeline(const QGstPipeline &);
     QGstElement gstElement() const { return QGstElement(gstCameraBin.element()); }
 #if QT_CONFIG(gstreamer_photography)
     GstPhotography *photography() const;
@@ -117,6 +119,7 @@ private:
     QGstElement gstDecode;
     QGstElement gstVideoConvert;
     QGstElement gstVideoScale;
+    QGstPipeline gstPipeline;
 
     bool m_active = false;
     QString m_v4l2DevicePath;
diff --git a/src/plugins/multimedia/gstreamer/mediacapture/qgstreamermediacapture.cpp b/src/plugins/multimedia/gstreamer/mediacapture/qgstreamermediacapture.cpp
index 8eb37ac06..4a5fbe6e6 100644
--- a/src/plugins/multimedia/gstreamer/mediacapture/qgstreamermediacapture.cpp
+++ b/src/plugins/multimedia/gstreamer/mediacapture/qgstreamermediacapture.cpp
@@ -93,11 +93,13 @@ void QGstreamerMediaCapture::setCamera(QPlatformCamera *platformCamera)
         QObject::disconnect(gstCameraActiveConnection);
         if (gstVideoTee)
             setCameraActive(false);
+        gstCamera->setPipeline({});
     }
 
     gstCamera = camera;
 
     if (gstCamera) {
+        gstCamera->setPipeline(gstPipeline);
         gstCameraActiveConnection = QObject::connect(camera, &QGstreamerCamera::activeChanged, this,
                                                      &QGstreamerMediaCapture::setCameraActive);
         if (gstCamera->isActive())