I use Intel Media SDK 2013 for decode the h264 video,but the speed is slowly.Who can tell me why it is?

I use Intel Media SDK 2013  for decode the h264 video,but the speed is slowly.Who can tell me why it is?

the SDK  have the sample decode project, I changed the function  ParseInputString  in sample_decode.cpp

insert  some code like this :

pParams->videoType = MFX_CODEC_AVC;

char* test_my = "D:\\win32\\1080pTst.h264";

TCHAR* haha = char2tchar(test_my);

memcpy(pParams->strSrcFile, haha,2*wcslen(haha)+1);
pParams->bOutput = true;

char* test_dest = "D:\\win32\\Tst_yuv_1080.yuv";

TCHAR* haha_dest = char2tchar(test_dest);

memcpy(pParams->strDstFile, haha_dest,2*wcslen(haha_dest)+1);

pParams->bLowLat = true;

I deleted the for() sentence in the function (ParseInputString )

Right now  it  can work ,but the decode speed is solwly, decode the 2048*1536 video ,  its  real frame rate is 11,the std frame rate is 18.

And when I decode the 1080P video ,its real frame rate is 17, but the std frame  is 30.

WHO  CAN TELL ME WHY?    SHOULD I SET SOME PARAMETER?   PLEASE ANSWER  ME   ,THANK YOU !