How do I access a FairPlay protected stream's frame in avplayer?

when i played a fairplay streaming by avplayer,calling copyPixelBufferForItemTime on AVPlayerItemVideoOutput the pixelbuffer returns NULL.is there any way to get the pixel buffer from a stream that is protected using FairPlay on iOS or apple's APIs in order to display FairPlay stream on an OpenGL texture in 3D space?

Any luck?

How do I access a FairPlay protected stream's frame in avplayer?
 
 
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