VTB failure on OS X 10.9

[RJVB]

As mentioned in my previous ticket, I have a long-standing fails-to-work issue with VTB in QMPlay2 on my Mac (2011 MPB 8.1 running OS X 10.9.5). This hardware acceleration does work in VLC as far as I can tell, so a priori it's not that my OS is too old (VTB was introduced in 10.8 btw).

I've been trying to trace the origin of the problem but get stuck somewhere on what appears to be a C++ problem...

In FFDecVTP::open():

av_hwdevice_ctx_create(&m_hwDeviceBufferRef, AV_HWDEVICE_TYPE_VIDEOTOOLBOX, nullptr, nullptr, 0)

does not fail. The subsequent operation

vtbOpenGL = make_shared<VTBOpenGL>(m_hwDeviceBufferRef);

also appears to succeed (I get a VTBOpenGL instance with its own, non-null copy of m_hwDeviceBufferRef).

Things go wrong in OpenGLWriter::setHWDecContext(): the dynamic cast from the HWDecContext instance to a OpenGLHWInterop fails. With some trace output:

bool OpenGLWriter::setHWDecContext(const shared_ptr<HWDecContext> &hwDecContext)
{
    auto hwInterop = dynamic_pointer_cast<OpenGLHWInterop>(hwDecContext);
    auto hwInterop2 = dynamic_cast<OpenGLHWInterop*>(hwDecContext.get());
    qWarning() << Q_FUNC_INFO << "hwDecContext" << hwDecContext.get()
        << "hwInterop" << hwInterop.get()
        << "hwInterop2" << (void*)hwInterop2;
    if (hwDecContext && !hwInterop)
        return false;

I get virtual bool OpenGLWriter::setHWDecContext(const shared_ptr<HWDecContext> &) hwDecContext 0x11e4061c8 hwInterop 0x0 hwInterop2 0x0

As far as I can tell this makes little sense: VTBOpenGL inherits OpenGLHWInterop inherits HWDecContext so unless something fishy is going on with the shared_ptr implementation a VTBOpenGL instance passed as a hwDecContext pointer should be dynamic-castable to a OpenGLHWInterop pointer.

Any idea how to figure out what goes wrong and why, here?

How crucial is the use of shared_ptr?