If and when you get this working. I have found for example; using this option to trans-code a video file to ProRes take long to encode. It's some time to rejoin the video file back together. (The same holds ture with having the fast-start option turned on when trans-coding to ProRes.)
This can take up to as much as twice the time to accomplished depending on how fast your drives are...
This opion however works great when encoding to MPEG-2 or h.264.