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This weekly course covers the most common questions videographers encounter when shooting and editing with DSLR cameras, from choosing a frame size and frame rate to understanding moiré. Authors Rich Harrington and Robbie Carman will also help you understand the impacts of compression and the difference between cropped (or micro 4/3rds) and full-sized sensors in cameras, and much more. This continual FAQ guide is a handy way to find the answers to the questions that plague you the most.
Richard Harrington: So in the pro world, people will say, oh HDMI, that's consumer technology. It's not a stable signal you know and we talked about before how the cables can easily come unplugged. You know they're just--they're designed to get plugged in. They're not really good under tension. Pros use a technology called SDI and tell me more about it. Robbie Carman: Well SDI or Serial Digital Interface is absolutely a pro-level kind of connection. And there's a couple of reasons that it's you know preferred by pros.
First is the distance that the cables can be run. You can run SDI for extremely long distances. Richard Harrington: And this is if you have the camera in one place and the monitor somewhere else, or a live switching situation, you might need to actually get the footage from the camera that's at the front of the room to the back of the room for switching. Robbie Carman: Right, and with un-powered HDMI cables, you know un-equalized and un-powered cables, you're typically in that 30, 40 maybe at the most, depending on the quality of the cable about a 50-foot range before you are going to get signal degradation or no signal at all.
Where SDI on the other hand, can go for much, much, much longer distances. The other thing I think is important about SDI is that the actual connections, or the connector type that SDI cables use, is a BNC or a Bayonet Neill-Concelman connector to lock in the actual connector. Richard Harrington: You're such a geek. Robbie Carman: Yeah, I win Jeopardy every night! And so the BNC connection allows you to actually lock in the cable. Richard Harrington: Yeah. Robbie Carman: So if you stepped on it, accidentally somebody walked by and snagged it, it's not going to pop out of the actual connector itself. That's not always the case with HDMI.
We talked about previously that HDMI is sort of a fragile interface and the pins can easily get bent, the cable can get pulled out. Now there are locking HDMI cables, but they're just not all that common. They're more expensive, they require a slightly modified port. So often times you want to be able to you know use HDMI, because after all these cameras they don't have SDI ports on them. They have HDMI ports on them. But you might want to be able to use SDI as well, in the case of running to a monitor that's really far away. Richard Harrington: Or if you already have an existing pro-monitor like you know as a video production company I have multiple professional monitors. Robbie Carman: Yup.
Richard Harrington: And HDMI was previously thought of as only a consumer format, so it was often left off of professional monitors. Robbie Carman: So you may have a monitor that's a couple of years old that doesn't have HDMI but has SDI. Richard Harrington: Yeah and so just for compatibility, so in this case like all things you know, any video pro you say, show me your adapters. They've got bins full of audio adapters, video adapters, cable adapters. There are adapters to go from HDMI to SDI, but they do require power. Robbie Carman: Yeah and we have one of them right here. This one is made by AJA, others are made by Blackmagic Design, and there are other manufacturers.
But basically the way that these work is that they're a little hardware box like this, and as you pointed out they do require power. So you need to make sure that you have a power source nearby. And basically what happens is that you pipe in HDMI onto one side of it and then on the other side, in the case of this AJA one, we can actually output two HD-SDI signals, and actually that's how we're viewing something up here on this little field monitor right now, that's HD-SDI. Richard Harrington: Yeah one is going to the monitor and then we're sending one out to a recorder, so as we cut to that so you could see you know this is what the HDMI signal looks like converted to SDI.
You're really not going to see any quality loss; it's just more for compatibility. Now these types of boxes range in price for about $250-$300? Robbie Carman: Yeah you know, they're not inexpensive but they're not the most you know expensive piece also. And they're one of those things that I feel like you know if you're not using it everyday, that's okay. It still might be worth the purchase, because the last thing you want to be is in the situation where you are on set somewhere and you have to make a specific type of connection, and you know, say HDMI to SDI, and you don't have that ability to do so. These boxes also, by the way, can go the other way; not nearly as needed for DSLR production, because oftentimes we're not going SDI to HDMI, but they do exist.
Richard Harrington: So both HDMI and SDI can coexist together and work very well on a professional set. By default HDMI will work as is, just get good cables. If you need to use the professional option of HD-SDI you're going to need a converter box and pick up those heavy-duty cables with the BNC connector.
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