sorry. wasnt finished with my posting.
DVCPRO 50 is natively 720 x 480. When captured via firewire, this is what you will get…all the FCP sequence presets are set for this.
If using a capture card, like AJA Kona, and capturing via SDI, the image size is 720 x 486…they simply add black lines to the top and bottom to fill in the remaining pixels.
You must use the Easy Setups provided by AJA (or create your own) to work with 720 x 486 DV50 footage. If you use the Apple ones, they assume you captured natively from firewire and have 720 x 480 footage…thus forcing you to render when using footage that does not conform to this size.