I read here http://ca.answers.yahoo.com/question/index?qid=20111021153855AAtfRTw
that a Composite Cable can carry 1080p HD video, but I was wondering if the BlackMagic Design Intensity Shuttle Thunderbolt can support HD input through composite. I know that it can support 1080p through HDMI, but I am not sure about Composite support. If not, does it support HD through Component? I am looking for a way to record footage from my computer, but it outputs an HDCP protected signal through HDMI, so I am looking to convert to an analog format, but would prefer to not have to also buy a converter to go back the other way again.
Composite cables can't carry HD signals at all, don't see where you got that idea, even from the answers on that link. I believe composite is limited to 480i or less.
Component video can do 1080p, but most devices limit it to 1080i.
What kind of content are you trying to record from your computer? You may be able to use a screen capture program, or a different program to directly convert the movie file into a different type without copy protection. You may be better off looking around in the HTPC section here for help.