Portable Video Production – SDI, HDMI, Cabling
So one of the big challenges when doing live video production is actually getting the video signal to the right place. Composite video was easy – cheap cables, cheap connectors, fairly bad quality but acceptable if you have a decent camera. Long VGA cables for projectors are outrageously expensive but have been very difficult to get rid of. For a while pro outfits would use long component multicores, but those are even more expensive and unwieldy. Using the consumer HDMI standard over anything more than 5-10 metres is impractical and requires amplifier boxes or something like a CAT5 sender and receiver.
In developing my portable production studio, I decided early on that I would need to adopt the professional SDI video cabling standard (actually, 3G HD-SDI) for both the camera and output to video projectors and screens. This allows full 1080i video over single coaxial cables that are far more flexible than HDMI or component. A toolbox of different gadgets would allow HDMI video sources to be converted to SDI, and the SDI outputs from the switcher to be converted to VGA or HDMI at the video projector – or connected directly if we hired in high end projectors with an HD-SDI input.
The cheapest source of high quality SDI cable I found is the Thomann SSSnake BNC video cable at £75 for 100m. It comes with the Neutrik rearTWIST HD BNC connectors fitted, which I found to be invaluable. Standard cheap BNC connectors have a locking ring that needs to be twisted to connect or disconnect the cable, which is quite difficult in a cramped high density panel. The Neutrik connectors are designed so that the whole of the back of the plug can be twisted, which saves time and potential damage. I decided that all of the external cables would be done with this more expensive connector. Having bought the 100m cable I cut it down to two 40m lengths and a pair of 20m lengths.
The next job was termination. The idea with BNC connectors is to use a crimp tool rather than mess around soldering, and the gold standard is a “gas tight” connection where there’s no issue with air getting in and causing corrosion. Unfortunately the Neutrik recommended tool costs several hundred pounds – seriously – for a one trick pony. After reading a lot of spec sheets and diagrams I eventually found one on amazon for fifty quid that does the job nicely (n.b. the photo on Amazon is wrong). I also got a coaxial stripper. Now… I can’t stress this highly enough… if you’re planning on making SDI cables, get a coaxial stripper. I can’t believe I’ve made so many cables in the past and didn’t spend five quid to get one. After a bit of fiddling it get the various bits of the cable end cut to the right lengths and really speeds up cable termination.
Blackmagic Design sell a dizzying array of different broadcast converters that are all very high quality and cost several hundred pounds each. Since I wanted a few of them, I decided to test a cheaper option from Amazon. There are a number of different companies selling rebadged devices, but there are probably only three or four different designs. I went for the Lingsfire Mini 1080P Converter at £29.90. With much anticipation, I connected up the Canon HV20 camera to the converter, ran the 40m cable back to the switcher… and… nothing! After a week of frustration, trying out various ideas including reterminating the cables, I decided to plug the converter into the HDMI output of my laptop. It worked! I borrowed a Sony camera and found that its HDMI output worked fine into the converter as well. Hmmm…
I then got hold of one of the Blackmagic converters from eBay at a decent discount. That worked fine with the HV20, so it looks like there’s some issue with using the cheap converters with the Canon cameras. Annoying, but when you can get the cameras for a hundred quid, it’s still cheaper to find second hand broadcast converters to go with them. Having heard negative reviews of the cheap converters, I took the opportunity to do a side by side comparison between the Lingsfire and the Blackmagic unit using the Sony camera. I could see no difference at all in picture quality, and both worked fine over the 40m cable.
Blackmagic Design sell a nice battery powered converter that’s designed for use with a handheld camera to avoid dealing with a power cable in addition to the SDI. Unfortunately they cost over £200 and are actually quite bulky and heavy for a camera op to have attached to their camera for several hours. The Lingsfire converter works with the Sony camera that I want to use handheld (the Canons will be in fixed positions probably) and has a 5V power input. I have a 2000 mAh battery sitting in a drawer that’s intended as a USB phone charger. Hmm… one USB to power connector later and we have a battery powered converter that’s considerably lighter than the Blackmagic device and costs about fifty quid all in, with a battery life running to several hours. I decided to put the pair into a bum bag (waist bag) rather than mess around mounting on the camera.
Finally I needed something to get a signal out to the projectors. I went for the Ex-Pro AV-Pro SDI to VGA converter, which I’ve found to be good quality. It’s worth noting that each converter, and the Production Switcher itself, introduces delay into the video signal. It’s a bit disconcerting using yourself as a subject and seeing the movement happen a quarter to half a second later. I initially thought that the quality of the video, by the time it had been through multiple standards conversions and projected via a VGA projector, was poor. After watching several pre-recorded videos through the system I’m convinced it’s actually very good, but of course it would be lovely to project in a higher resolution.
Next is to put it all together.