Let's start in the past: the film cameras you're (probably) accustomed to working with had a video tap that gives analog video, or composite video. Read the following if you're a REAL nerd:
Composite video is an analog signal, as in it's a modulated video signal carried over the cable from camera to your monitor. As a modulated signal, it's susceptible to attenuation, noise, interference, etc. Otherwise, the signal itself IS the video. Since it attenuates over distance, often times weak signals were amplified by adding a video distribution amplifier to "beef up" the strength of the signal. As the wiki article says, let's called this CVBS.
Now, we have all these fangled HD digital cinema cameras, and usually their monitor or video outputs HD (some cameras don't have a specific "MONITOR" feed, so we just tap one of the video outs). Now, the camera itself is digitizing the image, sending the video to internal storage as well as video outputs. They come out in a format called HD-SDI.
HD-SDI is digital signal, in that it is not a modulated signal like CVBS, but rather a stream of data whose signal constitutes a transmission of images.
To use a household analogy, your old school telephone line is an analog signal. Your internet connection, ethernet cables, etc are a digital signal.
So, HD-SDI signal carries an HD video image, and connects to an HD-SDI input on a monitor, recorder, or some other bulkhead jack with a receiver in mind. To any receiver not expecting a serial digital interface signal, it won't know what to do it and disregard the signal. Likewise, to any receiver expecting a modulated signal, be it NTSC, PAL or SECAM, it won't know what to do with an SDI signal and ignore it.
Now, for some confusion: SDI, being a digital signal, can carry standard definition much like it can carry high definition. The signal carries less data, but it's a digitized signal all the same.
Lots of accessory manufacturers sell things and say, "Yes, our product transmits/records/handles SD as well as HD!"
Technically, they're not wrong. Yes, that device does transmit/record/handle standard definition, but they handled it in a digital format: NOT CVBS. Their product is already set up to handle a digital interface, regardless of the resolution. What their product is generally not set up to do is handle an analog signal (unless they specifically say that it does).
Most of us think of our world in HD or SD: HD means HD-SDI and SD means CVBS. What we're thinking of is 2 different technologies, but in our heads, it's just a video feed. Many accessories out there will say, "Yes, we do SD!" and we think it to mean "Sweet, I can use this on my film camera jobs with an SD video tap as well as my Alexa jobs!" IT DOES NOT.
Products I've seen that are misleading in this way include:
- Decimator MD-DUCC - Specifically says it cross-converts SD to HD, HD to SD, HD to HD, SD to SD... but in actuality, it only does all those cross conversions in SDI. Yes, it still has HD to SD down-converting, but even I made the mistake thinking it would convert CVBS to HD-SDI. Nope.
- Atomos Samurai - a few operators have told me that the Atomos people have told them it records SD. Again, that's correct... it records standard definition when inputed as SDI. No, it does not demodulate an NTSC analog signal, convert it to digital and then store it.
- Switronix Recon - I think a few operators bought one, expecting it to transmit SD. Yes, it transmits SD-SDI, but not CVBS. To my knowledge, one of the few transmitters I know that transmit CVBS and HD-SDI is the Boxx Meridian.
p.s.- I kinda hate the new post editor. What does it leap back 5-10 words randomly when I hit backspace!?!