DM644x Digital YCC Output

If I have a image in DRAM that I want to pass to a THS8200 chip and I'm using the VPBECLK to clock my data to the THS8200, does the VPBE just clock out the active portion of the image or does it try to copy out the full image (including the front porch, back porch, sync et al) from memory?  What registers control where to copy from to the YC output?  I think my image (which is from a bitmap and is in RGB format) should be in YCbCr color space because the davincifb driver I'm using does not have the CLUT tables for the RGB->YCbCr conversion (I'm using the one from http://focus.ti.com/dsp/docs/dspsupporttechdocsc.tsp?sectionId=3&tabId=409&familyId=1302&abstractName=spraad7).