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This topic comprises 2 pages: 1 2
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Author
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Topic: Dolby discontinues the Dolby line of servers
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Marcel Birgelen
Film God
Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012
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posted 12-22-2014 04:24 PM
It doesn't matter if you use HDMI, Ethernet, PCIe or a bunch of pigeons with USB sticks around their necks. In any case you need something on one side to get the bits into and on the other side something to get the bits out of their lower level transmission protocol(s).
You encrypt the bits before you put them into your magic pigeons and decrypt them once you've captured them on the other side. This way, the transmission is secured, even if it has to fly over North Korea first. Series 1 servers and projectors achieve this by using Dual HD-SDI with a layer of encryption around the actual video bitstream. HD-SDI was chosen at the time, because it was a proven, stable technology for high bitrate video transmission.
We're talking about digital data here, so the underlying transmission technology, as long as it gets the bits from A to B in "one piece" at reasonable costs, is really not all that relevant. You could, for example, even use some bundled USB 3.0 links for the same purpose.
The reason why the industry isn't using HDMI or any other commonly used transmission technology is just paranoia. They wanted to make the path between "decrypted by the glory of the secret key" to the actual thing rendering the content on screen to be as short as possible.
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Marcel Birgelen
Film God
Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012
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posted 12-22-2014 06:06 PM
HDMI is by no means the golden standard and hasn't been around for as long as SDI, which later evolved into HD-SDI. Without going into too much technical details, even nowadays, there are still some things in favor of HD-SDI compared to HDMI for cetain purposes.
And like with many "standards", the nice thing is that you usually have multiple competing "standards", which all roughly do the same. HDMI competes, for example, with DisplayPort, which also competes with USB and Thunderbolt...
Those newest generation "household" interconnects are all evolving into bitrates where you do not need a custom interconnect for a particular type of data stream. Also, there's no real reason why not to use them for professional applications too. The Ethernet you use on your servers, IMBs, etc., is exactly the same as the ethernet in any other device.
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Marcel Birgelen
Film God
Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012
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posted 12-23-2014 02:11 AM
I guess we're running a bit off-topic regarding to Brad's initial intention with this topic ![[Wink]](wink.gif) .
You also have to look at what was available at the time the specs were written. This world evolves at a breakneck tempo and for professional applications it's not a good thing to bet on (yet) unproven technology. So, the decision for HD-SDI at the time was a sound one. But the decision for the "all integrated" IMB for the Series 2 systems wasn't all based on technology, it was primarily motivated by studio paranoia. Some of the interconnects we have today, like HDMI 2.0 and thunderbolt were not yet available at the time, but stuff like PCIe certainly was.
But essentially, if an interconnect can deliver the bandwidth, a low error count and a low amount of jitter, why wouldn't it qualify to carry a video signal? If you look at what the industry is doing, you'll see they're almost all looking to move to one-fits-all interconnects. One of the forerunners in this aspect being Apple. They're pushing hard to go the Thunderbolt route, where you run everything from your keyboard up to your 4K... ahum retina display over the same interconnects and we're talking about serious bitrates here. Others are pushing more to the USB standard. It's also about licensing in some cases. Whereas for professional gear it doesn't matter if you need to pay a few bucks for a license, it does matter at low-margin consumer goods.
Ethernet might be a bit of a special beast, but that doesn't automatically disqualify it. While most of those interconnection technologies allow you to use TDM channels between devices, Ethernet only supports packets as its lowest addressable transmission payload. This means you need a bit more logic on either side to put stuff in packets and get it out on the other side. You will also some extra buffering on either side. Also, you cannot share the same clock signal on either side, you need to generate your own. This all sounds very expensive, but given the price of many of those circuits nowadays it's not so special anymore. Hence, you can perfectly run high bitrate, uncompressed video over Ethernet. The biggest advantage of Ethernet, due to its underlying design, is that it can be easily "regenerated". You essentially put in a switch or a repeater and this way you can carry it as far as you want. The downside still is, the gear to do 10GBit, 40GBit or even 100GBit Ethernet is still horrendously expensive, but those prices will come down considerably in the coming years.
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David Buckley
Jedi Master Film Handler
Posts: 525
From: Oxford, N. Canterbury, New Zealand
Registered: Aug 2004
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posted 12-23-2014 05:55 AM
quote: Marco Giustini
If HDMI is the golden standard, why it hasn't replaced all the existing professional video standards on the planet?
I think you'll find most video professionals don't consider HDMI to be a professional internconnect, more a consumer internconnect. They hate HDMI with as passion. Mostly because of HDCP, it must be admitted, but also because HDMI cables are short, and to go any appreciable distance the signal needs to be electrically converted to something else.
quote: Marcel Birgelen
Ethernet might be a bit of a special beast, but that doesn't automatically disqualify it. While most of those interconnection technologies allow you to use TDM channels between devices, Ethernet only supports packets as its lowest addressable transmission payload.
There are digital audio formats like AES509 and HyperMAC which use the ethernet physical layer (layer 1) (relatively) low cost chipsets and wiring, and do something different layer 2 up. So they aren't compatible with ethernet networking, but leverage that technology to provide low cost audio transport.
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Marcel Birgelen
Film God
Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012
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posted 12-23-2014 07:15 PM
quote: Marco Giustini
Apple develop their own technology. D-Cinema is a small world. You cannot expect Barco or Christie to develop a variant of HDMI or Ethernet to carry what they want. I see your point, but wouldn't that be 'horribly expensive' to do?
Thunderbolt was originally developed by Intel. You don't need to develop a variant of HDMI, PCIe, Ethernet, etc. Everything you need can be developed on top of those protocols. And if you develop on top of HD-SDI or HDMI really doesn't differ very much. Thunderbolt might get more interesting in the future, as they promised an optical version which should be able to achieve the full bitrate at about 300ft.
quote: Steve Guttag
HDMI is particularly bad for cinema as it is a consumer format with a friction based connector
The lack of proper locking mechanisms is probably the biggest drawback of most "consumer interconnect" and a HDMI connector often provides less friction than e.g. USB. But then again, practically all power connectors are also of a friction based design...
Technically, HDMI is not all that bad though, it can achieve impressive bitrates at short to medium distances and components are really cheap compared to many other solutions.
DisplayPort is in many regards superior to HDMI, their connector design is better and the newest standard can go up to 32.4 Gbit/s. It's also royalty free. Unfortunately, DisplayPort is fighting a losing battle. They should, maybe, also consider changing their name, as DisplayPort can function as a generic digital interconnect for almost anything, just like the newest iterations of USB and HDMI.
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