In some case when gstreamer is used with namespaced qt classes the build process will be fail. To resolve please put all qt class declartion into qt namespace.

for example in file clocktime.h the 22th line should change from 
class QTime;

to:
QT_BEGIN_NAMESPACE
class QTime;
QT_END_NAMESPACE

this process does not affect any existing or new sources with normal Qt build. But in some cases, for example Qt compiled with namespace or namespaced headers (like WinCC_OA app plugin development) the classes will be declared in right namespace.