Aw, jeez, the talent's wearing black. A very bad move. A darker shade of green would have allowed both tracking and chroma keying, but it's too late for that.
After applying a hefty Dope Slap to the individual who decided that black tracking marks were a good thing, it will be time to get busy. Grab a big honkin' pot of coffee and set up a cot in the office, because you'll have your work cut out for you. Very time-consuming and painstaking.
This will require rotoscopig by hand. Sorry. I doubt Rotobrush can make the task any easier.
It will be particularly challenging if the footage is highly compressed -- DSLR's shoot highly compressed footage, for instance. Such footage is just God-Awful for effects work. The reason -- 3/4 of the color information gets thrown away! You get just enough color info to fool the human eye... but you won't fool a computer.
Chroma keying is all about the edges. You need nice, clean edges to get a nice, clean key. But because highly-compressed footage makes weird colors at the edges -- 3/4 of the color info is gone, remember -- it takes a lot to get a good-looking key.
So when you rotoscope by hand, you'll have to match the behavior of the key so the edge of the black jacket won't look different as it passes from green background to black background.
Now, that bleak scenario only applies if this was shot on a cheap, crummy camera for effects work like a DSLR or a consumer handicam. If it was shot using a better camera and recorded to a codec that preserved more color information, your task will only be painstaking and time-consuming. It won't be painstaking, time-consuming and bleak.
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA