d3d11window holds one buffer to redraw client area per resize event.
When the input format is being changed, this buffer should be cleared
to avoid mismatch beween newly configured shader/videoprocessor and
the format of previously cached buffer.
...for color space conversion if available
ID3D11VideoProcessor is equivalent to DXVA-HD video processor
which might use specialized blocks for video processing
instead of general GPU resource. In addition to that feature,
we need to use this API for color space conversion of DXVA2 decoder
output memory, because any d3d11 texture arrays that were
created with D3D11_BIND_DECODER cannot be used for shader resource.
This is prework for d3d11decoder zero-copy rendering and also
for conditional HDR tone-map support.
Note that some Intel platform is known to support tone-mapping
at the driver level using this API on Windows 10.
Don't specify the resolution of backbuffer. Then dxgi will let us know the
actual client area. When upstream resolution is chagned, updating the size
of backbuffer without the consideration for client size would cause mismatch
between them.
Use consistent memory layout between dxva and other shader use case.
For example, use DXGI_FORMAT_NV12 texture format instead of
two textures with DXGI_FORMAT_R8_UNORM and DXGI_FORMAT_R8G8_UNORM.
