HDMI
Introduction
HDMI was originally designed in 2002 as a short point-to-point cable for the transmission of
1080P signals with audio and control data between a source and sink (Display). It was
designed for “Plug and Play”.
These days, with bandwidth being up to 10x the original specification, HDMI signal integrity
is more fragile than ever, and often suffers problems caused by voltage drops, interference,
capacitive rise-times and incompatibility between different brands.
HDMI signals are digital, so unlike analogue AV (where you might hear or see signal
interference), problems are often exhibited as a complete lack of video or sound, or issues
with HDCP (High-Definition Copy Protection).
HDMI issues are more common with Home Cinema installations because:
- HDMI is no longer point-to-point, since an AV/AVR is in the signal path.
- Bandwidth is high because Home Cinema applications demand high resolution, HDR
and lossless multichannel audio. - Manufacturers application of the HDMI standard can lead to incompatibilities, even
though they will be compliant with the standard. The most common issues with
HDMI in Home Cinema applications are:
a. AppleTV
b. Cable Boxes
c. Kaleidescape Movie Players
d. LG TVs
e. Sky Q, Glass or Stream - Extended distances between the source, AVR and Display often introduce problems
and may require:
a. HAOC or AOC cables
b. HDBASE-T solutions
c. AVoIP - Installation practices are out-of-date with the latest specifications, including:
a. Inadequate CAT cable or screening for HDBASE-T
b. Poor bend-radius compliance for CAT or Fibre cables
c. Power supply issues through choice of extender
AV/AVRs are often incorrectly blamed for HDMI issues in Home Cinema applications, when
it is almost always that the complexity of installation or the method used to connect the
display (sink) that is the cause.
This document provides best practices and recommendations for trouble-free Home
Cinema installations with HDMI. In every example it assumes that the AV/AVR and source
components are cited in the same rack, with an extended distance to the display.
A brief explanation of the HDMI 2.1 Standard
In 2023 most source components use the HDMI 2.0a Standard, which supports up to 4K at
60Hz with HDR. The maximum bandwidth is 18Gbps. HDMI 2.0b adds support for HLG
HDR.
However, most Displays and Home Cinema projectors have at least one HDMI 2.1 port
which supports higher resolution/bandwidth. Manufacturers may choose whether these
ports support 24, 40 or 48Gbps.This varies according to the frame rate and resolution
supported by the source and display. Examples of HDMI 2.1 sources are:
- AppleTV4K (3rd Gen.)
- Playstation PS5
- Some PC Graphics Cards (e.g.: NVIDIA RTX 3080)
- Xbox One Series X
In addition to higher resolutions and frame rates, HDMI 2.1 also brings extra features,
optionally supported by HDMI 2.1 sources and displays:
- Dynamic HDR – allows content to set the dynamic range on a per-scene basis or
even frame-by-frame. - Variable Refresh Rate – adapts refresh rate to match content. Designed
predominantly for Gaming. - Quick Media Switching – Significantly reduces black screen time between source
selection - Quick Frame Transport – Frames are transferred between source and sink at a much
higher rate, reducing latency.
HDMI 2.1a adds HDMI Cable Power, which provides up to 300mA so that active
HDMI® Cables can be powered directly from the HDMI Connector, without attaching a
separate power cable. HDMI2.1a has only very recently been added to the standard and has
very limited support so-far.
When choosing a solution for HDMI connection between the AVR and Display, it is
important to consider whether you need to allow for HDMI 2.1, even for futureproofing,
before commencing installation.
ARC and eARC (Audio Return Channel)
HDMI has supported ARC since HDMI 1.4. It provides a digital audio signal from the Display
back to the AVR or Soundbar and requires CEC to function. ARC signals are only ~1Mbit/s
so multichannel audio formats are compressed. A common example is Dolby Digital+
eARC was first supported in HDMI 2.0 and is fully supported in HDMI 2.1. eARC signals are
~37Mbps and can provide High Bitrate Object Based uncompressed audio from the display
back to the AVR/Soundbar. A dedicated eARC data channel in the HDMI cable allows for
mandatory Lip Sync Correction. eARC still uses CEC to allow control of standby, mute and
volume on the AVR.
Important: Many HDMI extender solutions do not support eARC and may not
support ARC.
Configuring and Connecting Sources
The minimum HDMI cable specification for source components should be a Premium
Certified cable, but we recommend using an Ultra-High-Speed cable. Both types must be
certified by HDMI LA.The cable length should not exceed 2m.
The HDMI link integrity from start to end in the signal path should be tested to the
maximum required resolution/bandwidth with approved HDMI test equipment (e.g.: Murideo
MU-FXHD-KIT-8K).
In the absence of suitable test equipment, a Premium Certified UHS Cable should be
connected between the AV/AVR and the Display/Projector and should be no longer than 5m
(or the maximum certified length), e.g.: SCP 992UHS-5M.
Set the highest resolution, HDR type and audio settings required on each source and check:
- Is the AVR correctly detecting the Audio CODEC, and can you hear playback?
- Is the Display/Projector switching to the correct resolution and bitrate?
- Are the video and audio stable as you switch between sources and toggle AVR
power?
If source signals are taking a long time to appear on screen it is generally an indication that
there is an issue with the lower speed parts of the HDMI process, such as Voltage drop,
EDID or HDCP. See the troubleshooting section of this document for solutions.
Extended HDMI Distance to Display
Almost every Home Theatre application requires an active HDMI extension between the
AV/AVR and Display. There is no “right or wrong” choice for this provided that the solution
chosen is fully compliant with the HDMI standard. When considering HDBASE-T this also
includes the CAT cable used for the link.
When choosing your solution, remember to consider:
- Will the sources now or in the future require HDMI 2.1?
- Is ARC or eARC a requirement?
- Is there likely to be AppleTV, a Games Console or PC in the installation?
The following section is a guide to the different options for HDMI signal extension. The
capability table later in this document summarises this and will help you choose the right
solution.
Active Optical Cables (AOC/HAOC)
Active Optical cables have components that convert the high-speed TMDS/FRL signals
(which carry the picture and sound) and send them over fibre optic cores in the cable. Most
are HAOC, a hybrid solution, where the other cores in the cable are copper and carry
voltages and signals for power, EDID and encryption (HDCP).
All of the HAOC cables sold by Habitech meet the requirements of HDMI2.0 or above. Our
recommendations are as follows:
Cleerline SSF-48UHD-AOC Cables meet the HDMI2.1 standard at 48Gbps.
- Supports ARC and eARC (20m Max.)
- 8K60 4:4:4 (DSC) 48Gbps
- LSZH
- Uses Cleerline Fibre. HDMI plugs can be cut and replaced for fibre HDMI in the
future.
Netvio EX-HC-24 Cables meet the HDMI2.0 standard at 18Gbps.
- Supports ARC (not eARC)
- 4K60 4:4:4 18Gbps
- LSZH
Netvio EX-HC-48 Cables meet the HDMI2.1 standard at 48Gbps.
- Supports ARC and eARC (20m Max.)
- 8K60 4:4:4 (DSC) 48Gbps
- LSZH
SCP 995AOC Cables meet the HDMI2.0 standard at 18Gbps.
The Display connector on these cables has a removable Micro HDMI connector which
makes the cable easy to pull through tight routes/conduit.
- Supports ARC (not eARC)
- 4K60 4:4:4 18Gbps
- LSZH
SCP 996AOC Cables meet the HDMI2.0 standard at up to 18Gbps.
These cables are designed for outdoor applications and feature an armoured jacket and
waterproof HDMI plug housing.
- Supports ARC (not eARC)
- 4K60 4:4:4 18Gbps
Wyrestorm CAB-HAOC-xx Cables meet the HDMI2.1 standard at 24Gbps.
- Supports ARC (not eARC)
- 4K60 4:4:4 18Gbps
- 4K60 4:4:4 HDR 20.05Gbps (HDMI2.1)
Wyrestorm EX-HC-48 Cables meet the HDMI2.1 standard at 48Gbps.
- Supports ARC and eARC (20m Max.)
- 8K60 4:4:4 (DSC) 48Gbps
- PVC Jacket (not LSZH)
Extender Sets (HDBASE-T)
HDBASE-T is a popular option for extending HDMI because the extender sets can use CAT
cable. However, many lower cost extenders sacrifice features and bandwidth to meet a price
point.
HDBASE-T does not support HDMI 2.1, which means frame rate is limited to 60FPS or less
and HDR is not possible without using 4:2:2 or 4:2:0 chroma subsampling.Therefore, it is not
a suitable option for High Framerate applications like Xbox One X or Playstation 5. Future
content with AppleTV 4K will also be limited.
HDBASE-T 2.0
HDBASE-T 2.0 supports HDMI 2.0a and has a maximum encoding rate of 9.2Gbps. It has
native support for:
- 4K/60 4:4:4 (no HDR)
- 4K/30 4:2:2 (with 10/12bit HDR)
- 4K/30 4:2:0 (with 10/12bit HDR)
Optional support:
- ARC (not eARC)
- DSC (Display Stream Compression, also known as VLC)
Does not support:
- High Frame Rate 4K (e.g.: 4K120 PS5)
- HDMI 2.1
HDBASE-T 3.0
HDBASE-T 3.0 supports HDMI 2.0b and has a maximum encoding rate of 16Gbps. It has
native support for:
- 4K/60 4:4:4 (no HDR)
- 4K/60 4:2:2 (with 10/12bit HDR)
- 4K/60 4:2:0 (with 10/12bit HDR)
- Enhanced Audio Return Channel (eARC) and ARC
Does not support:
- High Frame Rate 4K (e.g.: 4K120 PS5)
- HDMI 2.1
Cabling for HDBASE-T 2.0/3.0
While many manufacturers advertise compatibility with CAT5E and CAT6 cabling, this is
generally for lower resolution and bandwidth applications.
Home Theatre components often peak at the maximum bandwidth for HDMI and therefore
need the full bandwidth of the HDBT specification.
The latest advisory from the HDBASE-T alliance is that a suitable CAT6A U/FTP cable
should be used with correctly terminated shielded connectors. A list of certified cables can
be found on the HDBT Alliance website
CAT6A U/FTP cables should always be terminated correctly, using suitable 10G Connectors.
Correct shielded connections are essential. Due to the larger diameter of U/FTP cables,
always use a field plug rather than crimp type.
Recommended HDBase-T Extenders
The Netvio HT3-4001-10 Extender set is HDBaseT 3.0:
- 4K60 4:4:4
- 4K60 4:2:2/4:2:0 HDR
- Supports eARC
Not recommended for AppleTV4K, Kaleidescape or PS5 due to lower frame rates with HDR.
The Wyrestorm EX-70-H2 Extender set is HDBaseT 2.0:
- 4K60 4:4:4
- 4K60 4:2:2/4:2:0 HDR
- Supports ARC (not eARC)
Not recommended for AppleTV4K, Kaleidescape or PS5 due to lower frame rates with HDR.
Extender Sets (AVX)
AVX is a competing technology to HDBASE-T. It originates from the SDVoE industry
standard and is comparable to HDBASE-T 3.0. However, unlike HDBASE-T, the transmission
method isn’t proprietary.
AVX is based on the IEEE 10G Ethernet standard and is less susceptible to cable
interference. It can be connected using either shielded or unshielded CAT6A cable, or
(optionally) fibre.
Like HDBASE-T, AVX does not support HDMI 2.1, which means frame rate is limited to
60FPS or less and HDR is not possible without using 4:2:2 or 4:2:0 chroma subsampling.
Therefore, it is not a suitable option for High Framerate applications like Xbox One X or
Playstation 5. Future content with AppleTV 4K will also be limited.
Recommended AVX Extenders
The Wyrestorm EX-100-H2-EARC Extender set is AVX:
- 4K60 4:4:4
- 4K60 4:2:2/4:2:0 10/12bit HDR
- Supports eARC
Not recommended for AppleTV4K, Kaleidescape or PS5 due to lower frame rates with HDR.
Extender Sets (AVoIP)
AVoIP offers more flexibility than other extender options, since one encoder can stream to many decoders, and extension distances are only limited by the network infrastructure.
In some applications it may be preferable to have an AVoIP Receiver at both the Display and the AVR, rather than running a cable from the AVR to the Display. If the HDMI output of the AVR is not connected it will result in no EDID exchange between the AVR and Display and may result in no audio from the AVR. See the troubleshooting section for solutions to this.
Low bandwidth AVoIP solutions that use H.264 or H.265 (HEVC) are not recommended for residential AV, since most streaming services are already decoded H.265 streams and reencoding results in generational loss. This exhibits itself in picture artefacts and motion judder. H.264/265 also increase latency in the encode/decode process.
The preferred solution for encoding AVoIP in residential applications is JPEG2000. This is
used by Crestron, Netvio and Wyrestorm amongst others. A 4KUHD JPEG2000 encoder
typically generates a ~850Mbit/s stream which can be distributed using multicasting through a properly configured gigabit network. In a point-to-point application (e.g.: AVR to Projector) additional network components are not necessary (but may be for initial configuration).
When choosing an AVoIP solution for Home Theatre, consider encoding quality and chroma subsampling. Not all JPEG2000 CODECs are the same. Higher resolutions and HDR modes can lead to reduced frame rate. Look for a 600MHz pixel clock which can support the full bandwidth of HDMI 2.0.
Recommended AVoIP Solutions
Wyrestorm NetworkHD™ 500 Series:
- 4K60 4:4:4
- 4K60 4:2:2/4:2:0 HDR10/12bit HDR10, Dolby Vision, HLG
- Supports eARC
- 600MHz Pixel Clock
Not recommended for AppleTV4K, Kaleidescape or PS5 due to lower frame rates with HDR.
Summary Table
The table below shows the capability of each solution discussed in this document. Note that not all cables and extenders are the same. Pay careful attention to the cable construction or chipset type and distance. Examples:
- Habitech recommends Cleerline 48G HAOC Fibre cables because the fibre inside is
Cleerline SSF and can be reused with different connectors in the future. It has been
tested extensively in Home Theatre applications. - Many HAOC cables claim to be 24G but do not support HDMI 2.1
- Some HDBASE-T and AVoIP extenders have limited bandwidth, a lower pixel clock or distance support, which may limit the image quality
HDMI Troubleshooting
Active Cables
HAOC cables have glass/plastic fibres in them to transmit the high speed data using TMDS (HDMI 1.0-2.0) or FRL (HDMI 2.1). The lower speed communication data is still
communicated over (thinner) copper wires.
When an HDMI signal is initiated the Source device sends a 5V signal to the HDMI receiver on the Sync (Display), which in-turn sends a 3.3V HPD signal back to the source to start negotiation of EDID.There is a small tolerance of +/- 0.3v in the standard, which can be problematic with longer cable runs.
The HDMI specification only requires a current of 55mA for 5V signalling. This means that cables with smaller gauge wires over longer distances can cause voltage drops and capacitive loading, which in-turn causes one or more of the following problems:
- Audio or Video Dropouts
- Long time for the image to sync to the display.
- Mode out of range message
- Frequency out of range message
- HDCP not supported message.
These problems can be intermittent and difficult to replicate. But the following solutions
often stop the problem recurring:
5V Power Injector
Installing a 5V Power Injector at the Sink (Display) with a regulated 1A plug-top supply will provide enough current so that the sink can return a reliable HPD signal and power the TMDS/FRL lanes from the source. In some cases it may be necessary to install a 5V injector at each end of the cable.
Ethereal JR3
The JR3 is an inline HDMI device has an integrated voltage comparator which makes DDC/EDID comms more robust. It also strips capacitive loading from the HDMI cable. The JR3 is also particularly useful for sources which strictly adhere to the HDMI specification (e.g.: Kaleidescape, AppleTV).
Ethereal AIO2
The AIO2 is a multifunction powered inline HDMI device. It stabilises the voltages on hot plug, DDC/EDID and TMDS/FRL lanes on the HDMI cable and provides voltage matching for both input and output. Additionally, there is a contact closure port which
interrupts the hot plug signal on the HDMI cable, causing the source and sink to renegotiate. This is particularly useful when an AVR is switching sources, because issues can often be resolved by simple reinitiating the hot plug process. The port can easily be connected to a relay output on a control system and programmed to momentarily open when source selection is changed. Additional electronics in the AIO2 make sure that the correct timing is used for the HPD signal.
HDBASE-T
HDBASE-T is generally robust but can become problematic when used in high bandwidth applications (e.g.: 4KHDR).
When cabling for HDBASE-T extenders, always use CAT6A U/FTP cable and always screen and terminate it correctly at each end, using suitable field connectors. Install the cable according to its bend radius guidelines and do not run the
cable next to high voltage cabling.
In some instances, particularly where an HDBASE-T receiver is locally powered (floating power supply) or connected to a sink on a different circuit, the extender set may not function reliably. In this instance try replacing the field connector at the receiver end with an unscreened type. Always retain the screen at the source end, and never use a screened cable without using a screened connector on at least one end.
AVX
Since AVX uses the IEEE 10G Ethernet standard, and is less susceptible to cable interference, there are rarely issues in the link between extenders, as long as CAT6A is used. However lower source voltage from the AVR can still be a problem, as can EDID issues at the display. A common solution to image instability would be to use a 5V power injector or JR3 at the display end of the chain.
AV Over IP (AVoIP)
In a point-to-point application, the extenders usually need to be configured first, using the management software provided by the vendor.
In all cases, category cabling between the extenders should be CAT6 or above (CAT6A
ideally).
In applications where multiple receivers are used (e.g., One receiver
for the AVR, one for the Display), it is often necessary to provide an
EDID on the HDMI output of the AVR, even if it is not used.
Pre-programmed and learning EDID plugs (pictured) are readily available online and will provide the AVR with the EDID it needs to return to the source and decode audio. Not all AVR applications need this, so it is worth testing first (keep a spare in your stock).
In multi-point applications it is necessary to use a network switch that is managed, nonblocking and has a switch fabric/backplane that exceeds the capacity of the total amount of ports in full duplex mode. (so a 24 port switch with 4 x 10G uplinks would need a backplane of at least 56Gbps). It also needs to fully support IGMPv2/3 and be correctly configured.
The Netgear AV Line switch series are specifically engineered for AV applications and are
extremely simple to setup.
Where AVoIP applications span across switches the uplinks between the switches must
exceed the capacity of the transmitters. E.g., when 12 TXs are used the total bandwidth is 12x 850Mbps = 10.2Gbps. So it would be necessary to use 2 x 10G uplinks between switched in a LAG group.
Each manufacturer has a switch guide for configuration with AVoIP products on the Habitech website.