HWDecoder

This class demo how to use VideoToolbox to make iOS hardware decode

HWDecoder Step

// 1. Get SPS,PPS form stream data, and create CMFormatDescription, VTDecompressionSession
// 2. create  CMFormatDescription
// 3. create VTDecompressionSession
// 4. get NALUnit payload into a CMBlockBuffer
// 5.  making sure to replace the separator code with a 4 byte length code (the length of the NalUnit including the unit code)
// 6. create a CMSampleBuffer
// 7. use VTDecompressionSessionDecodeFrame
// 8. use VideoToolBox Decompress Frame CallBack to get CVImageBufferRef