New User Format Question

[Lawrence Anthony]

I have the following pipeline that I want to output I420 (or any format other than YUY2) :  

gst-launch -v videotestsrc  ! ffmpegcolorspace  ! videoscale ! videorate ! 'video/x-raw-yuv,FORMAT=I420, width=640, height=480' !  v4l2loopback sync=false max-lateness=50000 device=/dev/video1

But when I run the stream through mplayer it says it is YU12:

Opening video decoder: [raw] RAW Uncompressed Video
Movie-Aspect is undefined - no prescaling applied.
VO: [xv] 640x480 => 640x480 Packed YUY2 
Selected video codec: [rawyuy2] vfm: raw (RAW YUY2)


I cant make this value change no matter what colorspace I specify.  Am I missing something simple here?