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SD composite, HD-SDI, SD-SDI - just a note

hd sdi cvbs

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#1 William Demeritt

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Posted 28 November 2012 - 08:35 PM

As more and more HD digital cinema cameras are trickling out, so too is the market growing for accessories and tools to work with those cameras. Inevitably, the question of backwards compatibility and multi-use comes up: does that onboard recorder receive SD? SDI? What tools do I need to make it work as many places as possible? Since I get a few questions from time to time (and I seem to be the resident geek, what with Afton working and being a Dad and all), I thought I'd write up a small primer.

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:

http://en.wikipedia....Composite_video

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.
Just some thoughts to keep with you this Christmas shopping season, as well as going into this digital future we're facing. If you're considering buying a tool or accessory, and it has anything to do with the video signal, MAKE SURE you ask the sales rep to distinguish if it works with CVBS, SD-SDI and HD-SDI.

p.s.- I kinda hate the new post editor. What does it leap back 5-10 words randomly when I hit backspace!?!
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#2 Brian Freesh

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Posted 28 November 2012 - 08:58 PM

Good post! Can we pin it?

Just found out the other day that Clairmont, when they send a film camera out, almost always (or is it always) rents their film cameras with an HD IVS. I assume this is the norm at the other big houses too.
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#3 Joel San Juan SOC

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Posted 02 January 2013 - 08:31 AM

Is the Bolt CVBS then?

J.
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#4 William Demeritt

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Posted 02 January 2013 - 11:30 AM

Joel: no sir. The Bolt accepts only SDI (SD-SDI or HD-SDI) over the BNC in. Does not accept CVBS.
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#5 Joel San Juan SOC

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Posted 02 January 2013 - 06:16 PM

Thanks William! :) Great to know

J.
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#6 Jarrett P. Morgan

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Posted 02 January 2013 - 07:46 PM

Great post William.

I know I am still "new" here, but if I may add to it:

all devices that say they accept HD-SDI won't necessarily accept all HD-SDI signals: There are several different flavors and standards of the signal and older monitors may not like the newer signals (if you want to get really nerdy into the various SMPTE standards, look here: http://en.wikipedia....rface#Standards ). This is most evident in cameras such as the Epic (mainly the Epic, actually) that outputs 1080/23.976P not PSF. I have run into several monitors (namely older Sony and JVC ones) that will not display the Progressive signal. If you run into this issue and need to have the image, you can change the camera output (either on the camera or through a box such as the Decimator Design MD-DUCC) to 720/60P, as this is defined within the old standard.

Just thought I would weigh in since I have run into the problem before.
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#7 Brian Freesh

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Posted 02 January 2013 - 09:31 PM

various SMPTE standards


Indeed.

I once had a professor from Turkey. One of his favorite complaints about moving to the US was how many 'standards' we have. He even took us on a complete historical tour of how we ended up with the current mess of standards in video/film/broadcast industries. Of course, that was before HD was a big thing. It's way more confusing now.
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#8 Jarrett P. Morgan

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Posted 02 January 2013 - 10:17 PM

various SMPTE standards

It's way more confusing now.


One of my favorite things is how everything has similar (and multiple) names as well (Component, Composite, CBVS, video, etc) and how connectors are used for various signal types. I can't tell you how many times I have been on set and video village is down and it is because a camera intern has plugged the SDI feed into the "Video" BNC input. It makes perfect sense, but doesn't work at all, haha
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#9 William Demeritt

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Posted 02 January 2013 - 10:28 PM

Sometimes during prep, I'll just cap the BNC plugs I know we won't be using, but especially the CVBS/SD/"Video Out" plug. Other times, I just make certain the PA or whoever plugging in the cable knows which one to go for, and why.
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#10 Jarrett P. Morgan

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Posted 02 January 2013 - 10:33 PM

capping them makes perfect sense. I may start doing that on production monitors. Good tip!
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#11 David M. Aronson

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Posted 03 January 2013 - 12:25 PM

Great post. This really should be pinned. I'd love to see HDMI mentioned in there since that's a cluster of all sorts of nonsense. Component would also be interesting to mention too.
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#12 William Demeritt

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Posted 03 January 2013 - 02:11 PM

David: As JP mentions, and I mentioned in the initial post, the overuse of generic BNC bulkhead connectors is as much the cause of this problem as the lax language of "Yea, it does SD" (when they really mean "Yea, it does SD-SDI, but not CVBS"). I haven't had too much confusion over HDMI so far: it's HD pretty much always, never confused for analog, and doesn't suffer from SMPTE schizophrenia. Component is interesting, but I haven't seen a camera supporting component in a while.
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#13 Jarrett P. Morgan

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Posted 03 January 2013 - 10:04 PM

HDMI does have different standards (versions, most of the time now-a-days you see 1.3 or 1.4), but most of the time they merely adopt new and crazy resolutions and frame rates (like 4K and 3D stuff we don't see).

I have run into the issue of having certain HDMI devices not like it when a decimator is outputting PSF (although the decimator PSF is actually identical to i, just in a different wrapper). There is no standard for PSF over HDMI that I am aware of, so that is the only place I have been tripped up.

One advantage to the "handshake" that HDMI does is that the receiving end will sometimes tell the sending end what type of signal it can take.

Though for the most part the whole "handshake" thing is an annoyance in time. Oh well. Consumer standards being annoying.
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#14 Victor Lazaro

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Posted 04 January 2013 - 10:19 AM

Signal conversion has always and always will be a head hake, no matter what standard we introduce. I love BNC regardless to what goes through because you only need one kind of cable to use with every format of video. It is sturdy, durable, and lockable(unlike HDMI). Of course you have the HD SDI that requires a better quality cable but then it is all the same, unlike the consumer side with HDMI (and the HDCP protections, thick cable, easily breakable and unplugs quickly) the DVI ( bulky connector and no sound)...
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#15 martin klimpar

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Posted 12 February 2013 - 04:31 PM

is there any (cheap) way how to convert CVBS (composite) to SD SDI?
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