I've seen that some higher end digital SLRs do 1080p HD video. I am guessing that they use the H264 codec. I also suspect that the audio is not as good on the SLR used as a video camera. Can anyone tell me advantages and other disadvantages to using a high end SLR as a video camera
You've already correctly guessed that a camera designed primarily for still images may not necessarily be optimized for smooth operation as a TV camera.
Yet some people just swear by the images that DSLRs make, and to acquire those stunning images, they're willing to put up with a lot of aggravation. In no particular order, here are some of the problems:
You have to get a special rig to put camera controls in a place for easy use.
You probably need special camera support gear, too; a normal plate on a tripod just won't do.
You have to record audio separately from the video.
You have to get an effective way to simulate a viewfinder; every camera manufacturer has its own method for monitoring video.
Many editing applications (FCP in particular) can't use the video in its native acquisition codec.
These cameras have what's known as a Rolling Shutter: very bad for shooting even moderately-fast horizontal motion, or any kind of motion under strobe lights.
That's a partial list, but it at least you can appreciate that a DSLR won't replace a normal TV camera for every situation, and that you REALLY have to be in love with the images they make to commit to using one.
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA