|History of HDMI Versions|
Let’s take a look at the history of the HDMI versions released up to this date, the features delivered in each version, and the use of these features in each respective HDMI standard.
An interesting pattern emerges from looking at the new HDMI formats and their capabilities:
sRGB - A basic RGB format used by the HDMI predecessor, DVI. The compatibility with DVI is an important feature as it is used occasionally when PC’s are connected to a consumer HDMI display through the use of a DVI to HDMI passive dongle. During the transition from DVI to HDMI the feature was very important because millions of cable Set Top Boxes were made with DVI outputs connected to HDMI equipped displays. The use of this feature will decrease in time when more and more computers will be equipped with HDMI output ports. At present there is no Cable or Satellite Set Top Box that offers DVI connectivity.
YCrCb – A basic default HDMI format use by all HDMI sources today.
8 channel /192 kHz/24-bit audio capability - A basic Audio format, the 2CH stereo subset used for all HDMI source to flat panel TV connections today. Flat panels have two speakers and require this format for audio display.
1080p video at full resolution – This format received somewhat misguided use at the marketplace. There are two 1080p formats: 1080p/24 frames per second and 1080p/60 frames per second. All HDTV capable media today, such as Terrestrial ATSC, Satellite, Cable, and Blu Ray carry 1080p/24 among other HDTV formats such as1080i/60 and 720p/60. None of them carry 1080p/60. However, most of the larger and higher quality flat panel TV’s do feature 1080p/60 format as the native resolution. Therefore, it is believed that 1080p/60 is a full resolution video. It is true, but 1080p/60 is not available as a native format. To create a 1080p/60 resolution, the Blue Ray, STB or TV itself must up-convert the incoming native video at 1080p/24, 1080i/60 or 720p/60 to 1080p/60 for display. Where is the better location to perform such up-conversion? If it is done at the source we encounter two problems: The quality of the up-conversion is dictated by a low cost scaler chip in the source device and the transmission line (HDMI or CAT5 cable) is weighed down with a 1080p/60 format that demands twice the bandwidth compared to1080p/24 or 1080i/720p and limits the connectivity to half distance. Therefore, using Blu Ray at 1080p/24 and Satellite or Cable Set Top Boxes at 1080i is most practical and provides the best quality connection. Nevertheless, 1080p at 60F/s or 24F/s is used today in Blu Ray to TV connectivity.
Consumer Electronic Control (CEC) - Extensively promoted as “the control bus” for interconnected consumer products, it is virtually never used…. It is not a surprise for most industry insiders because there were many “control bus” proposals over the past years: power line CE bus, Firewire 1394 and others. The basic problem is a business issue. The consumer products within one brand may have a chance to listen to each other over such a “control bus”. Each brand is only interested in the customers buying more of their products to create a working system at home and may make an extra step for these components to interact properly. However, intra-company communication is not beneficial to the manufacturers because it encourages the consumer to buy different components from different brands… Therefore CEC remains a technological curiosity never promoted or used.
DVD Audio support - This is an important technology basically opening a de-facto surround sound encoding Dolby AC3 and other formats to be available over HDMI. This format is used extensively in any surround sound installation. It is successfully provided by Satellite, Cable, Terrestrial, DVD and Blu Ray HDMI sources.
Super Audio CD (DSD) support - The Super Audio CD format was introduced as a last high quality attempt to hang onto CD media. It has never been accepted by the mainstream market. CD’s are quickly loosing the competition with downloaded audio. This format is available, but is probably never used in DVD or Blu Ray players.
Deep Color - Deep color creates a more accurate image quantization from the usual 8 bits per color to 12 bits per color or more. Up to now, Deep Color is rarely used for actual TV displays outside the high-end workstations and other specialized production or post-production markets. It is difficult for the human eye to see any difference between 8 bits and 9 bits per color. There are special patterns that can be used to demonstrate the benefit of increased bit depth, but in regular HDTV images these effects are very hard to notice. Therefore, Deep Color is most likely a marketing feature that takes space and bandwidth costs and offers no perceivable benefit. In addition, the TV content production industry is geared for Terrestrial, Satellite and Cable distribution that is bound by 8 bit encoders and decoders. The reasons for extra production investments into Deep Color encoding systems are not clear because they will only benefit Blu Ray distribution.
xvYCC - Even though digital television currently uses 8 bit color (0 to 255 quantization levels) in most implementations, it is actually 16 to 236 or 220 quantization levels. The color gamut, or color representation, of each Red, Green and Blue is designed within BT.709 standard for 16 to 236 level systems. 16 to 236 is a legacy issue basically to be compatible with analog YPrPb interface. A fully digital interface, such as HDMI, is capable of a full 0 to 255 performance without increasing the 8 bits per color specification. The xvYCC is a new, more advanced, color gamut standard that uses the full range of values (from 0 to 255 in an 8-bit space) to represent colors. It is a great idea that does not take away bandwidth but can be demonstrated to the untrained eye quite easily with almost any TV content. The problem here is backwards compatibility. Both studio camera or film telecine and TV need to be xvYCC to use this feature. Some consumer TV’s are starting to support xvYCC and this may in turn promote production to become xvYCC compatible as well. As you see from Picture 1 below there are more accurate and rich color representation in xvYCC color space compare to HDTV color space. Even though HDTV color space was considerable improvement compare to SDTV color space.
Auto Lip Sync - Auto Lip Sync is a capability of HDMI receiving chips to re-align Audio to be in sync with Video. Audio can run out of sync because video processing often involves frame memories that delay Video and make Audio run ahead. Recently, more and more content is digitally encoded and decoded via MPEG2 or more advanced MPEG4, H.264 and VC1 codec’s. By Definition, all these systems create synchronized Audio and Video. In addition, one frame delay (16 milliseconds) is way below human sensitivity, which is about 30 milliseconds, to realize lip-sync issues. So, in principal we can have a Video/Audio time mismatch but in practice it is getting harder and harder to find with the digital delivery systems that are now in place for all TV delivery media. To take true advantage of auto lip-sync in HDMI1.3, all components in chain must cooperate: the HDMI source must be1.3 and include special time stamps on the video and audio bit streams and the HDMI receiver must be 1.3 and be able to read these time stamps and take action. Since conversion to 1.3 for consumer delivery sources is very slow and consumer sensitivity to lip-sync is very small – the implementation of this feature remains very questionable.
Dolby TrueHD and DTS-HD capability - The practical implementation of this feature follows the same basic trends we observed for Super Audio CD, Deep Color, xvYCC and Auto lip-sync. Both production and display must be implemented to use this feature. The problem is that it takes an extremely high quality Audio Home Theater system, well done content production, and a trained listening ear to actually hear the difference between Dolby AC3 and Dolby TrueHD/DTS-HD. In addition, the TV content production industry is geared for Terrestrial, Satellite and Cable distribution that is bound by AC3 as a compressed multichannel Audio format. Some Blu Ray discs began supporting this audio format. Marketing efforts to promote this format may result in an increase in use. However, actual use will always be limited to only very high end audio display installations.
Ethernet Channel - This is the latest installment of the increasing HDMI capabilities. This connection set up in such a way that it is fully support Ethernet switching even when the HDMI port is not active and/or the HDMI switching device is in standby/sleep mode. Let’s say Blu Ray is connected to the Internet and connected through HDMI to a TV set. The TV set is able to connect to the Internet through Blue Ray while you watching another HDMI inputs for example Cable STB. Basically any HDMI device connected to the Internet and offering HDMI Ethernet Channel in their specifications must allow any other HDMI Ethernet Channel device connected over HDMI to access the Internet. That feature can save some Ethernet wiring when network of devices connected to HDMI all offer HDMI Ethernet Channel. The Internet connectivity is quickly added to Blu Ray players to offer streaming TV services. Some TV’s are also demonstrated with Internet access for streaming TV. It seems that both Blu Ray players and TV’s has independent access to the Internet through wired or WiFi. It is not clear if we have any clear need for Internet connectivity through a HDMI cable that connect these devices.
Audio Return Channel - Once the TV switches to the desired HDMI input, this channel makes digital audio available for display on an external A/V receiver like product, but does not feature input switching capability. Of course, you can use a regular A/V receiver for input switching, but the receiver already switches HDMI inputs and already has an audio stream available for the display. So what is the advantage here? In theory, you can take away the input switching responsibilities from the A/V receiver, and system integration can be easier by needing to only control your TV. However, you still need to make adjustments to the A/V receiver’s audio volume. Therefore, your TV remote would need to have IR codes for the Audio receiver or you would need to program a universal remote for control over the TV and the Audio receiver. I am not sure that we see any savings in programming. The cost reduction for an A/V receiver without switching capabilities is very small because most of the hardware in these products is responsible for audio decoding and amplification. Another opportunity to use this feature is in situation when TV receives ATSC RF input but user wants to display ATSC channel sound on the external surround sound system. The Audio return channel will provide that ATSC audio to the surround sound receiver through the HDMI connection.
3D over HDMI - 3D capable TV’s and Blu Ray players are shipping in US. HDMI.org fixed mandatory 3D formats. 3D is very attractive in retail shop. However, the creation of the titles will be painfully slow unless gaming and other special content will kick in…
4Kx2K/24 display format - This format has 4 times the resolution of 1080p/24. It may be of interest to the content production community. Presently, only DVI digital interface offers this capability. However, the copy protection aspect of HDMI is of no use to community. It is not clear if HDMI will comp7ete with DVI or Display Port in this market. I think it will take a significant amount of time, if ever, for 1080p resolution to be “not enough” for use in the consumer and commercial markets. An additional hurtle is that the camera, telecine, and the TV all need to be at this resolution to take advantage. It will take 4 times the encoded bandwidth data rate to transmit 4Kx2K/24 compare to 1080p/24. That means to transmit one 4Kx2K it will take the space of four current HDTV channels or 24 current SDTV channels. That is a big obstacle in bandwidth for the limited Cable, Satellite, and especially Internet delivery systems.
HDMI 1.1 remains the most practical and widely used interface today. There are some features of HDMI 1.3, such as xvYCC and Dolby TrueHD/DTS-HD, which have some potential for the residential and commercial marketplace. However, it remains to be seen if a global change and global investment in every aspect of video capture, production, and display will enable these features for wider use in the future. The 3D feature of HDMI 1.4 is very attractive and pushed hard by CE. 3D can work over HDMI 1.3 with proper handling of TMDS and EDID.
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