HDMI Cable length

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ClaytonMoore

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HDMI Cable length

PostWed Nov 10, 2021 5:05 am

Using the ATEM MINI PRO ISO, what is the longest reliable HDMI cable length ?
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mateuszszar

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Re: HDMI Cable length

PostWed Nov 10, 2021 8:03 am

If ActiveOpticalCable (fiber) - more than 100m

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Dave Del Vecchio

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Re: HDMI Cable length

PostWed Nov 10, 2021 11:30 am

It's not really possible to answer this question definitively with a single number, as the short answer is: it depends. The maximum HDMI cable transmission distance depends on several factors including:
  • Signal Format (resolution, frame rate, bit-depth, subsampling)
  • Cable Type (passive, active, optical)
  • Transmitting and Receiving Hardware
In terms of signal format, for example, a 1080p60 signal (at 8-bit 4:2:2 sampling) requires roughly double the cable bandwidth of a 1080p30 or 1080i60 signal (at the same bit depth and subsampling). Which would mean that when using the same HDMI cable you probably will be limited to shorter cable runs with 1080p60 than 1080p30 or below. The HDMI specifications recommend using High Speed HDMI cables for 1080p50 or 1080p60 signals, but allow Standard speed cables for lower frame rates. There is a chart of HDMI cable bandwidths for different signal formats here:
https://www.rtings.com/images/reviews/t ... -large.jpg

In terms of HDMI cable type, in addition to the official HDMI designations like Standard, High Speed, Premium, etc., there are also different types of cable construction. In passive electrical cables, which are the simplest type, there are essentially just a bunch of electrical wires inside the cable, from one connector end to the other. HDMI connectors have 19-pins, which means a lot of individual wires inside the cable, and as a result the wires themselves tend to be rather thin. But this has an effect on maximum transmission distance. So an HDMI cable that uses 24 AWG wires will be thicker than one that uses 28 AWG wires, but the thicker cable will likely also support longer cable runs.

In active electrical cables, there are still a bunch of electrical wires running the length of the cable, but these cables add an integrated circuit inside one (or both) connectors that improves the effective transmission distance. This active circuitry can be used to send the same signal format a longer distance over the same cable type or to reduce the thickness of the wires inside the cable (so now you could use 28 or 30 AWG wires for a cable length might have required 24 AWG or 26 AWG in a passive cable).

The third common HDMI cable construction is active optical cables. These cables also have integrated circuits inside each connector, but now transmission of the video data is primarily over fiber optic strands. The circuits in the connectors convert electrical HDMI signals from the device to optical signals for the bulk of the cable length and back to electrical signals at the other end. This allows for much longer cable runs and much thinner cables as well. In practice, most HDMI optical cables actually still have a few electrical wires that run the length of the cable (in order to support the bi-directional communication allowed over HDMI), but since high bandwidth video data is now sent over optical fiber, fewer electrical wires are needed.

Due to the technology involved and complexity of construction, optical HDMI cables tend to be quite a bit more expensive then electrical HDMI cables, and active electrical cables, in turn, are more expensive than passive ones.

The transmitting and receiving hardware also play a role in maximum transmission distance, as different devices use different HDMI transmission/receiving circuits that have different performance. This is obviously the factor you have least control over, as typically you want to use a particular devices together (like a particular camera and particular video switcher). But it's worth keeping in mind that there is some variation here, so just because one HDMI source (say a camera) sending a signal format at a particular resolution and frame rate (1080p60) works over a particular HDMI cable is no guarantee that another device (say a laptop) works sending the same signal format over the same cable type and length. Often it will, but sometimes not, often due to hardware differences.

With the background out of the way, these are the rough guides I use for maximum cable length with a given cable type:
  • Passive Electrical HDMI Cable: up to 8m (25 ft)
  • Active Electrical HDMI Cable: up to 15m (50 ft)
  • Active Optical HDMI Cable: up to 100m (328 ft)
In some cases you may be able to go further than that, in some cases perhaps less, depending on the factors mentioned above. And in terms of the HDMI optical cables, while 100m (300ft or so) is often the longest available for consumer-oriented cables, there some longer ones out there often intended for installation in buildings. For example, Celerity Technologies makes a 300m (1000 ft) HDMI optical cable, so you can achieve pretty long runs with the more expensive optical cables.
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Jeff P

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Re: HDMI Cable length

PostWed Nov 10, 2021 1:59 pm

Great info Dave.

Thanks for posting!
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ClaytonMoore

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Re: HDMI Cable length

PostWed Nov 10, 2021 6:47 pm

Wow great information thank you so much !!!!
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JacobN

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Re: HDMI Cable length

PostMon Nov 29, 2021 7:54 pm

Hey does cable length affect the ability for the Atem Mini to communicate Camera Control to the device?
My passive 30ft cables work fine, and I have a 100ft Active Optical Cable that transmits fine. But I just got an additional 75ft Active Cable that fails to display Preview/Live to camera or Allow remote camera controls.
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Dave Del Vecchio

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Re: HDMI Cable length

PostMon Nov 29, 2021 10:06 pm

JacobN wrote:Hey does cable length affect the ability for the Atem Mini to communicate Camera Control to the device? My passive 30ft cables work fine, and I have a 100ft Active Optical Cable that transmits fine. But I just got an additional 75ft Active Cable that fails to display Preview/Live to camera or Allow remote camera controls.
The camera control signals from the ATEM Mini are sent using the HDMI CEC (Consumer Electronics Control) communication protocol. The CEC protocol provides a low-bandwidth bidirectional serial communication channel between the HDMI source and sink device that is separate from the high-bandwidth video data transmission signals. CEC typically uses pin 13 of the HDMI connector. More background on the HDMI CEC protocol here:
https://en.wikipedia.org/wiki/Consumer_ ... cs_Control

CEC was added in HDMI version 1.0, so it isn't an especially new feature, although the CEC specs were amended a couple of times in some of the newer HDMI versions. Most HDMI cables do support CEC as I believe this is technically required at the HDMI cable level. But I suppose it's possible that some active optical HDMI cables do not conform to this aspect of the spec, as it requires the ability to send control data in the opposite direction from the video data flow.

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