If you have HDMI, you donât want to convert to composite video (blech) and re-encode! Use the HDMI!
I use a Blackmagic Intensity Extreme with a Canon HF G10 (thereâs a G20 now), into my Mac via thunderbolt. Quality is great!
I stream using Wirecast (expensive, but awesome piece of software). I combine the video from the Canon camera, with the cameras on my Macâs and USB cameras. I also use a cool app called âMobila Webcamâ, which lets me use the camera on my iPhone and iPad as a wireless webcam.
I donât know if youâll be able to stream from your GoPro wirelessly, I have the Hero 2 with Wifi Back. It would actually be quite cool with itâs ultra wide lens.
The way the Mobila Webcam app works is thereâs an app on your iPhone, and a companion application for your Mac/PC. It appears in your broadcast software as any other web cam (a virtual driver).
It looks like Blackmagic now has the âMiniâ single HDMI input, and I think youâll be able to use two at once (they are $137 a piece) for 2 inputs. I highly recommend their hardware, they have very strong driver support.
I had previously used CamTwist. Wirecast is MUCH better, CamTwist is great for free, but once your start to get into multiple sources and full HD, it starts to become a little cumbersom. Wirecast has tons of options for overlays, transitions, etc.
One thing to keep in mind, if you are going to be using HD sources, it becomes very CPU intensive pretty quickly. On my quad-core i7 MBP, things are pretty good, but it sucks up over 60% CPU using just the one HDMI and a few webcams. On my same vintage dual-core i7 13" MBP, it pegs the CPU pretty good.