The Canon 7d and 5d mark 2 are HD, so they can be used for HD broadcast work right?
This is a question I have come across a lot, together with the question "Can I use a DSLR for when filming for the BBC" and the answer is yes and no. A huge number of cameras are classified as HD as they record 1080p, i.e. they record 1080 horizontal lines of resolution (as opposed to standard definitions 480). However, the footage that they record is compressed in one way or another and this is where certain formats can be rejected by broadcasters. An iphone shoots "HD" so somewhere broadcasters have to draw a line and say what is and what isn't acceptable.
As far as the BBC is concerned HD DSLRs are not on their list of acceptable HD cameras as it stands now. The reason for this is the compression ratio. Without getting too geeky about this, cameras can compress images by ditching information, giving less resolution for chroma information than for luma (in simpler terms colour and brightness). This is expressed as a ratio, for example:
4:4:4 This would indicate no compression
4:2:2 Essentially some of the chroma info has been ditched here. That said, 4:2:2 is still a very high end HD recoding format (used on cameras such as top end HD XDCAM and HDCAM)
4:2:0 DSLR's compress footage into a format known as H.264, which puts them here.
However, every broadcaster has their own values of what they can accept as being HD, the BBC is probably one of the less forgiving broadcaster for this. Having said that, even in a BBC HD programme you are allowed a certain percentage of non "HD footage". You may not be able to use your 7d or 5d as the main camera, but you can certainly use it. (NB Something to be aware of here is that if the programme you are working on has lots of archive footage, you are very likely to use up all of your non HD allowance on the archive SD footage, and will have little left for shooting.)
Will this change?
The Canon 5d Mark 3 has yet to be vetted by the BBC (as of now Aug 2012), so we it is tricky to say whether it will be accepted as suitable for HD broadcast. The standard rule at the BBC is for cameras to shoot at 50 megs per sec, however, it isn't just about numbers, the Sony F3, which shoots 35mbs in camera is accepted as HD by the BBC.
With the 5d mark 2, both aliasing and rolling shutter were brought up as issues (along with the 4:2:0 ratio and H264 codec). These issues seem to have been resolved with the Canon 5d mark 3 and the codec has also been upgraded. Whether this will be enough to satisfy the engineers at the BBC we'll have to wait and see. As at the end of 2012 there is no word on this.
There is a lot of different information out there at the moment with regards to the Canon 5d mark 3, both in terms of data rate, and to what extent rolling shutter and aliasing issues have been resolved. Things have moved on so much since the 5d mark 2, new cameras have come to the market, most obviously the Canon C300, that resolve all of the issues the BBC and others had with HDSLR. In my opinion (if I had to guess) the BBC won't approve the 5d mark 3, there has already been lots of talk on the net about sharpness and moire. That said, it will always be possible to use it as a B camera to get into small confined spaces, as long as it only uses up a small percentage of any programme.