Luckily for most of us, camera manufacturers try to make it simple by processing all the signals within the camera. These signals are then written on to various media. Sometimes, as in the case of the Sony F65 or Arri Alexa, the choices of external recorders are clear cut.
But there are cases where the manufacturer provides a signal, usually uncompressed, via different ports. These signals are not thrown out haphazardly, but are arranged in a very specific way, in the same sense letters are arranged according to the rules of grammar and spelling. This is called a Protocol.
The three most common family of standards that you’ll find on many cameras are:
- Component Y’CbCr (Digital)
Since most of the cameras in this guide don’t use component I’m not considering it. But it still exists on many cameras, and provides a perfectly acceptable video signal, provided you remember my caveat in the External Recorders chapter.
The standards are precisely defined, and are very important indicators of compatibility between external recorders, monitors and other devices, and the video feed out of the camera. It’s supposed to make things easy, right?
You might be forgiven for thinking: If a camera has a specific standard, say SMPTE 292M (HD-SDI), and an external recorder has the same standard in its specifications, then they’ll be compatible, right?
Sorry to disappoint again. Manufacturers are notorious for providing incomplete or vague information in their specifications. Don’t believe me? Download the manuals and try sorting through the technical specifications.
Rule of thumb: Just because a signal is in a specific standard doesn’t mean you’ll get the best out of it. These standards are just packaging, nothing more. More often than not, it hides the dirty sampling and inefficient digital voodoo within the cameras themselves.
Think of them as egg crates. An 8-bit video feed has 8 slots, and a 12-bit feed has room for 12 slots. You can have 8 great eggs in an 8-bit crate, and 12 rotten eggs in a 12-bit crate. To know more, I strongly recommend you read Driving Miss Digital, so you are no longer prey to all this BS.
The chart should tell you that HDMI is geared for 2K and 4K, while HD-SDI is ‘only’ good enough for 1080p60. On the other hand, an SDI connection, using a BNC connector, locks on to the port, ensuring there are no unwanted disruptions. Furthermore, SDI is designed for long cable runs, like about 100 meters (328 feet) for HD. HDMI can only go up to 30 meters (about 100 feet) without an extender. With a good extender, it can equal SDI. But imagine how many HDMI connections does that make? The more the HDMI connectors, the greater the chances of one being dislodged.
Rule of thumb: Choose HD-SDI over HDMI whenever possible. It is designed for rough professional use. HDMI is designed as a consumer standard.
If you’re an Alexa user, you’ll be asking: How is it that the Alexa can output 3K out of dual HD-SDI? Well, they don’t use the SMPTE standard. They treat the two ports as just cabling, and have their own circuitry and protocol, called T-link.
The burning question at the end of the day is: If all this is murky, and information is scarce, then how does one select the right camera-recorder-monitor combination?
If the answer isn’t made plain by the manufacturers, then ask friends or your peers. If you’re still confused, then write to the manufacturer asking for specific help. If they don’t answer, or if the answer only makes it worse, then avoid that manufacturer.
Rule of thumb: If the service at sales is poor, imagine what service you’ll get once you have parted with your cash.
The most common reason for incompatibility within standards is the mismatch between field rates and frame rates, namely via interlacing, progressive feeds and psF feeds. To know more about these, please head over to my Understanding Terminology series and read the chapters that deal with these standards.
To keep it short: psF is a progressive feed split up into halves to mimic an interlaced feed, so that devices that can’t read progressive frames are fooled into reading them. These ‘legacy’ devices were designed at a time interlacing was king.
Rule of thumb: When in doubt, stick to progressive video. Only consider interlacing if shooting specifically for broadcast. Luckily, though, most broadcasters have begun accepting progressive video directly.