DNxHD failing to load on windows?

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I'm Using the pre-compiled FFMPEG which opencv uses by deafult for windows. I cannot get a DNxHD file to open as a cv::VideoCpature - either in a quicktime container or an MXF. I get a couple of "WinRT originate" errors, "The stream number provided was invalid" for mov and "The Media Source could not parse the byte stream" for MXF files.

Other common codecs tested fine, and DNxHD is opening fine on Mac (using separately compiled ffmpeg as cv requires)

So has anyone seen it working or have any ideas as to why it might fail on WIN10? I don't really have any ideas on how to dig deeper...