HDMI 2.0 and Support for 4K UHD Video
Blog by Ron Jones
This blog provides an update on the new HDMI version 2.0 standard’s support for handling 4K Ultra-HD video. I have included some specific information that I have received from an official source within the HDMI organization as well as some more general information about this new HDMI standard.
In early September 2013 the HDMI Organization released a statement announcing the new HDMI version 2.0 standard (referred to as simply HDMI 2.0 in the following discussion) has been approved and provided the following general information (more information is HERE) about the new capabilities enabled by this update to the HDMI standard:
HDMI 2.0 significantly increases bandwidth to 18Gbps and includes the following advanced features:
- Resolutions up to 4K@50/60 (2160p), which is 4 times the clarity of 1080p/60 video resolution, for the ultimate video experience
- Up to 32 audio channels for a multi-dimensional immersive audio experience
- Up to 1536kHz audio sample frequency for the highest audio fidelity
- Simultaneous delivery of dual video streams to multiple users on the same screen
- Simultaneous delivery of multi-stream audio to multiple users (Up to 4)
- Support for the wide angle theatrical 21:9 video aspect ratio
- Dynamic synchronization of video and audio streams
– CEC extensions provide more expanded command and control of consumer electronics devices through a single control point
For the following discussion, I am limiting the context to the 4K Ultra-HD video aspects of the new HDMI 2.0 standard, even though new audio and other features are included as summarized above.
The previous version of the HDMI standard was ver. 1.4b and the new HDMI 2.0 standard provides for backward compatibility. This means, for example, if you were to connect a HDMI 1.4b (or 1.4a) equipped display to a new video/audio source that is equipped with a HDMI 2.0 output, then the source device will only use the specific features that can be supported by the display. In this case none of the advanced features supported by HDMI 2.0 would be available while the specific features offered by HDMI ver. 1.4, and implemented by both the video source and the display, would be enabled by the source device.
As background, the HDMI 1.3 and 1.4 series included provisions for a ‘High Speed’ connections supporting data rates up to 10.2 Gbps. This was an increase over of the earlier versions of HDMI and the increase in bandwidth was added to support 1080p video signal signals at up to 60 Hz refresh rate (with HDMI ver. 1.3) and this 10.2 Gbps bandwidth was later deemed sufficient to support 1080p 3D video when that format was added with HDMI ver. 1.4. However, we now have 4K Ultra-HD (UHD) video displays and video sources coming to the marketplace and the need was seen for an even high bandwidth version of HDMI in order to support the more demanding variations of the 2160p UHD signals.
Products supporting HDMI 2.0 inputs and/or outputs may implement only a subset of the enhanced features defined by the new HDMI standard. Some early implementations of HDMI ver. 2.0 will only support the 10.2 Gbps data rate, as used for HDMI 1.3/1.4 devices, while other implementations will support the maximum 18 Gbps data rate allowed by the new standard. When a manufacturer indicates that their device has HDMI 2.0 inputs and/or outputs, they are expected to list (or specify) the specific enhanced features (such as video resolutions and refresh rates) that are supported by that device rather than specifically stating the maximum data rate their HDMI 2.0 implementation can support. It will probably be sometime in 2014 before full-bandwidth HDMI 2.0 chipsets become widely available to the consumer electronics manufacturers and in the interim we can expect to see some early implementations of HDMI 2.0 that only offer a limited subset of the capabilities defined by the HDMI 2.0 standard. For example, over the next couple of months Sony will be shipping several 4K UHD products, including new 4K UHD projectors, equipped with HDMI 2.0 ports. See the “First Look” at the new Sony VPL-VW600ES - HERE. However, it appears these products are using HDMI chipsets that are limited to 10.2 Gbps bandwidth as the specific 4K UHD video formats that Sony has indicated they will support does not include those that would require the increased 18 Gbps bandwidth allowed by HDMI 2.0. So far only Panasonic has announced new UHD products equipped with HDMI 2.0 ports (i.e., flat panel UHD TVs) that are specified to support the full 18 Gbps bandwidth.
Even those early HDMI 2.0 implementations that are constrained to a 10.2 Gbps bandwidth may be able to fully support the 4K UHD video formats used by the first generation of UHD video sources. However, with a 4K UHD version of Blu-ray Disc potentially coming to market as early as late 2014, it is possible that a more complete HDMI 2.0 implementation will be required to support the most capable 4K UHD video formats allowed by this next generation Blu-ray system. Even so, such displays equipped with early HDMI 2.0 implementations should still be compatible with the future, more capable, 4K UHD video sources due to the method HDMI uses to negotiate to find a format that can be supported by both devices. In this case the 4K UHD source should be able to provide the best 4K UHD format that can be supported by the connected UHD display device.
Factors that Drive Bandwidth Requirements
There are four primary characteristics of video signals, as listed below, that impact the bandwidth (data rate) requirements that must be supported by the HDMI ports and cables:
Video Resolution. For standard 2D HD each video frame can be as large as 1920 x 1080 pixels (i.e., 1080p) and for 4K UHD each video frame is 3840 x 2160 pixels (i.e., 2160p), while there is a commercial 4K video standard that uses slightly larger frames with 4096 x 2160 pixels. For full resolution 3D, each video frame must carry both the right and left sub-images that together make up the 3D image. This is done using the “frame packing” technique defined by the HDMI 1.4 standard. When 3D video is used each video frame passed across the HDMI connection has a little more than twice the vertical size (pixel count) as compared to a regular 2D video frame. For full resolution 1080p frame packed 3D, each frame is 1920 pixels wide by 2205 pixels vertically (1080 pixels for each the right and left images that are placed one above the other plus a 45 pixel high separator between the two images). This was discussed in a earlier blog –HERE. For 3D 4K UHD the 3D frame should be 3840 pixels wide by approximately 4365 pixels high (two 2160 pixel high images plus a small space between the two images). The larger the video frame then the greater the bandwidth needed to convey the signal across the HDMI connection. As a result, 3D video requires approximately double the bandwidth of otherwise similar resolution 2D video.
Video Refresh Rate for video signals can vary between 24Hz and 60 Hz and the higher the refresh rate the greater the bandwidth requirement. In this context the refresh rate relates is how many image frames of video per second are being conveyed from the video source to the display. For reference, virtually all movies are shot at 24 frames per second (fps) which can fully be conveyed by a video signal with a 24 Hz refresh rate. A very limited number of new movies may be available over the next few years that were shot at 48 fps or 60 fps, but 24 fps is expected to remain the dominate rate for theatrical movies for many years to come. Future UHD TV broadcasts and recordings of concerts or sporting events may be provided at frame rates up to 60 fps and ideally conveyed across HDMI with signal rates up to 60 Hz..
Video Bit Depth. This determines how many different shades of a given color and how many unique colors can be represented. Just about all of today’s HD video source material is limited to 8-bit depth while UHD standards allow for increased bit depths (e.g., 10-bit, 12-bit, etc.). The greater the bit depth that is provided, then the more shades and more unique colors that can be represented, but the higher the bandwidth necessary to convey the video signal.
Chroma Sub-Sampling is a means to reduce the amount of data required to convey the color information in the video signal. HD and UHD video signals can use different compression levels with chroma sub-sampling and the specific type being used is most commonly represented by 3 numbers. In this case the most common types used are: 4:2:0, 4:2:2 and 4:4:4. Of these types 4:4:4 represents no compression of the chroma information, 4:2:2 reduces the horizontal resolution of the chroma information by 50% while retaining the full vertical resolution, and 4:2:0 reduces both the vertical and horizontal chroma resolution by 50%. In all cases the luminance information (essentially the black and white information) is maintained at the full resolution. More information on Chroma subsampling can be found HERE. Video signals, when the 4:4:4 chroma sub-sampling is being used, require the greatest bandwidth while signals where 4:2:0 chroma sub-sampling is being used require the least bandwidth of the three types discussed above.
HDMI 2.0 Support for 4K UHD
There seems to have been some incorrect information floating around the web about what the capabilities and limitations are for HDMI 2.0 as far as supporting various types of 4K UHD signals. I believe some of this confusion comes from some early HDMI 2.0 implementations being limited by HDMI chips that only support the same 10.2 Gbps bandwidth as the current HDMI 1.3 and 1.4 chipsets. Below I have attempted to show which 4K UHD signal formats can be supported by these limited HDMI 2.0 implementations as well as the more complete set of 4K UHD signal formats that could be supported by implementations having the full 18 Gbps bandwidth and supporting the full array of signal types as defined by the HDMI 2.0 standard. I must qualify the following information by saying that I have not been able to obtain a copy of the HDMI 2.0 standard for review as that document is only available to companies that are formal (dues paying) members of the HDMI organization. Rather, I have had communications with an official from the HDMI organization who has answered a number of questions as to the specific 4K UHD signal formats supported by the HDMI 2.0 standard. In cases where I have seen neither published information or have received specific information from my contact at the HDMI organization, I have added a question mark (?) to the information provided below (see the note following the tables for more info). Also in the cases where I indicate use of 4:4;4 Chroma Sub-Sampling the same supported 4K UHD formats (i.e., resolution-refresh rate-max. bit depth) would apply for 4K UHD signals in RGB format. Also I have limited the following tables to only provide a summary HDMI 2.0 support for the 4K UHD format (3840 x 2160).
HDMI 2.0 (Limited to 10.2 Gbps bandwidth)
HDMI 2.0 Full Implementation (with 18 Gbps bandwidth)
* NOTE: I have been informed that the HDMI 2.0 standard supports 4K UHD 3D signals based on the frame packing technique as was defined in the HDMI 1.4 standard (for 1080p 3D video in that earlier version of the HDMI standard). I have not received information on what combinations of refresh rates, bit depths and chroma sub-sampling types are specifically defined by the HDMI 2.0 standard for 2160p 3D signals. This is why the above tables have question marks for the specific 3D signal types. However, I was informed that most all combinations of these signal characteristics are supported for 3D signals, as long as the signal bandwidth stays within the bandwidth limit (i.e., 18 Gbps for the maximum case). For the above tables I have attempted to include only 3D signal formats that stay within the applicable bandwidth/data rate limits.
Existing “high speed” rated HDMI cables should generally work for HDMI 2.0 installations where the bandwidth is limited to 10.2 Gbps. For cases where the 4K UHD video source, any intermediate AV Receiver, and the 4K UHD display (e.g., projector) are all equipped with HDMI 2.0 ports that support the full 18.0 Gbps bandwidth allowed by HDMI 2.0, then “high speed” HDMI cables may work for short cable lengths (e.g., 10 ft. or less), but active HDMI cables rated to support the full 18 Gbps bandwidth will probably be required for longer cable runs, such as from an AV Receiver to a ceiling mounted 4K UHD projector. Such active HDMI cables rated for 18 Gbps bandwidth should be available by the beginning of 2014.