GStreamer: implement unlock() in QGstVideoRendererSink.

There are cases where blocking operations happening in the video sink
need to be unblocked, that's why GstBaseSink has an unlock() virtual
function. Since our custom video sink blocks when starting and when
rendering a frame (while waiting for the main thread to actually do
these operations), we need to implement the unlock() function in order
to unblock these operations when requested by GstBaseSink.

Change-Id: I5cb19ea689e655f572729d931cefec8a4266c94e
Reviewed-by: Andrew den Exter <andrew.den.exter@qinetic.com.au>

src/multimedia/gsttools_headers/qgstvideorenderersink_p.h

@@ -96,6 +96,7 @@ public:
 
     bool start(GstCaps *caps);
     void stop();
+    void unlock();
     bool proposeAllocation(GstQuery *query);
 
     GstFlowReturn render(GstBuffer *buffer);
@@ -153,6 +154,8 @@ private:
 
     static gboolean stop(GstBaseSink *sink);
 
+    static gboolean unlock(GstBaseSink *sink);
+
     static GstFlowReturn show_frame(GstVideoSink *sink, GstBuffer *buffer);
 
 private:

src/multimedia/gsttools_headers/qvideosurfacegstsink_p.h

@@ -88,6 +88,8 @@ public:
     bool start(const QVideoSurfaceFormat &format, int bytesPerLine);
     void stop();
 
+    void unlock();
+
     bool isActive();
 
     QGstBufferPoolInterface *pool() { return m_pool; }
@@ -148,6 +150,8 @@ private:
     static gboolean start(GstBaseSink *sink);
     static gboolean stop(GstBaseSink *sink);
 
+    static gboolean unlock(GstBaseSink *sink);
+
     static GstFlowReturn show_frame(GstVideoSink *sink, GstBuffer *buffer);
 
 private: