second decoder calling mfxDECODE::DecodeFrameAsync return -17

Hi, 

I'm trying using API to do a multiple decoder application.

If I initialize decode session with MFX_IOPATTERN_OUT_VIDEO_MEMORY, only first decode session can decode well, the others failed while calling DecodeFrameAsync with returned code -17 .

But if I initialize with MFX_IOPATTERN_OUT_SYSTEM_MEMORY, I tried maximum 16 decode sessions and all work perfectly.

I referenced IntelMediaSDK-tutorial-0.0.3/simple_2_decode_vmem and have no idea what is the problem.

Any suggestions?

penny