The file preview/legacy/mfxvideo++.h is a preview implementation of "class MFXVideoSession"
which takes advantage of oneVPL API 2.0 functions for implementation selection and session creation.

Known limitations:
- The parameter mfxInitParam.ExternalThreads is not supported.
- The API version returned by MFXVideoSession::QueryVersion() may be different on platforms for which libmfx-gen is the default
runtime implementation.
- On Windows, accelerators selected using MFX_IMPL_HARDWARE, MFX_IMPL_HARDWARE2, MFX_IMPL_HARDWARE3, or MFX_IMPL_HARDWARE4
are always enumerated according to IDXGIFactory::EnumAdapters (i.e. D3D11) indexes, regardless of the acceleration mode selected.
On a multi-monitor or multi-adapter system, D3D9 and D3D11 adapter indexing may not match. Applications needing
to create a session on a specific D3D9 adapter should instead use the Dispatcher Configuration Property 
mfxExtendedDeviceId.DeviceLUID to select the desired adapter.
- Identical behavior between the production implementation of mfxvideo++.h and the preview is not guaranteed. Applications
may however define MFXVIDEO_CPP_USE_DEPRECATED when compiling the preview application to build with the previous implementation.