HapDecoderFrameAllocBlock Block Reference
This defines a block that returns an instance of HapDecoderFrame that has been allocated and populated (the returned frame should have a buffer into which the decompressed DXT data can be written). Providing the buffer into which DXT data is decompressed allows devs to minimize the number of copies performed with this data (DMA to GL textures being the best-case scenario). Use of this block is optional- but if you use it, you must populate the HapDecoderFrame’s dxtData and dxtDataSize properties.
typedef HapDecoderFrame* (^HapDecoderFrameAllocBlock) (CMSampleBufferRef decompressMe)