Decoded YUY2 frame from Microsoft NX-6000 using Media foundation

I am using Media foundation to capture from Lifecam NX-6000 webcam on Win7.

This camera supports MJPG formats. I am able to successfully set the the current media type to YUY2 format to get a decoded frame . 

hr = _sourceReader->SetCurrentMediaType(MF_SOURCE_READER_FIRST_VIDEO_STREAM, NULL, pType);

But, the sample that I receive using 'ReadSample' has a byte size of width*height*3 as opposed to the expected YUY2 frame byte size of width* height*2.

Any suggestions/comments on what could be happening here?

Thanks in advance.