Transparency in GVRVideoRenderer

[Oliver-Binns]

I need to implement transparency in GVRVideoRenderer.
The use case for this is playing a video over a 360° photo background to give a VR effect.

I have used Chroma Key blending with an input and mask image to implement the transparency in AVPlayerItem:

let filter = AlphaFrameFilter()   
filter.inputImage = request.sourceImage.cropped(to: sourceRect)     
filter.maskImage = request.sourceImage.cropped(to: alphaRect).transformed(by: transform)

Unfortunately, when passing this into GVRVideoRenderer, the view still has a black background.

How can I fix this?