Streaming the image
The other point to consider, is how to capture the image from the camcorder and stream it. With a webcam, this is all done for you; they are “USB class” devices so the computer will recognise them, as will live streaming software.
This is not the case for an HDMI (or even analogue or SDI) camcorder, so you will need an interface to capture the video stream and pass it to a service such as YouTube Live or Hangouts. This means buying a capture card, usually a PCIe card, or an external capture box using USB3 or Thunderbolt to connect to your computer.
Some live stream producers have had some success with game capture boxes but others report significant encoding delays, so it is best to look at those for broadcast. Matrox, BlackMagic Design and AJA make good interfaces. Note, though, that older Firewire cards aren’t useable with services such as Google’s Hangouts. Unless you also plan to buy or rent a vision mixer, you will need to allow for an interface for each camera you plan to use.
Again, there can be compatibility challenges, so try to have the capture card and computer you plan to use to hand before you pick a camera; manufacturer support does tend to be focused on pro cameras.
The last, but certainly not the least, point to consider is audio. One of the easiest and cheapest ways to improve the quality of Hangouts and live streams is to move away from using the webcam’s built in mic and separate audio. Google+ and YouTube Live make it very easy to select a separate audio input.
It may be you are already using a separate audio interface and a mic, in which case you can carry on doing so, and simply plug in a new camcorder and interface. But for the most flexibility, look for a camcorder with at least a 3.5mm (1/8-inch) audio jack.
Not all camcorders feature audio inputs, and many DSLRs also miss this feature. But it really is an essential, especially if you want to use the footage recorded in camera for later editing — and that’s another good reason to use a camcorder rather than a webcam. You also need to check that the camcorder’s audio stays in sync with the video over HDMI. It should, but keep in mind some camcorders’ headphone sockets only play delayed audio, so you need to check the HDMI feed on an external screen or ideally your capture hardware. Avoid using the camcorder headphone out as a substitute audio feed for this reason.
Next: Pro or semi pro?