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Format Wars: DisplayPort vs. HDMI

Posted by admin on November 4, 2015 11:25 am

If you finally switched to HDMI, you may be about to get caught up in yet another format war. The rapid-fire innovations stirring the audio/visual market have intensified over the last decade, leading the Video Electronics Standards Association (VESA) to develop an alternative interface: DisplayPort.

DisplayPort

While it may seem that DisplayPort is a successor to HDMI it’s really not, however, it is the successor to DVI/VGA. Just like when DVI came out in 1999, DisplayPort is currently primarily found on high-end cards and monitors. It wasn’t until around the mid-2000s when DVI started to appear on more mainstream computers, similarly, DisplayPort will eventually be found in an increasing number of monitors as there are more systems in the field that have DisplayPort built-in.

If it seems that we are just now hearing about DisplayPort, it may surprise you to learn that DisplayPort 1.2 came out in January 2010, even though DisplayPort-equipped 4K monitors are still relatively new. DisplayPort 1.3 was released in September 2014, making it a year old already, and at that point maximum link bandwidth increased to 32.4 Gbps.

DisplayPort was developed as a PC-to-monitor interface for computer graphic displays, and in those markets it is seeing a high level of adoption due to its amazing graphics capabilities for computer gaming. In the Professional A/V market, DisplayPort has made in-roads as well. The advantages of DisplayPort for commercial customers include:

  • Although the official spec does not require it, most full-size DisplayPort connectors have a locking mechanism that prevents them from being disconnected accidentally, where HDMI does not.
  • Commercial use of DisplayPort protocols is royalty-free, where manufacturers must pay a royalty for including HDMI into their products.
  • DisplayPort is based on a data packet structure similar to USB, and it is this packetization that allows other connectors to work with it. In fact, VESA has announced that products will be launched this year using the new USB Type-C connector, which is a reversible connector – meaning that the plug doesn’t have to be oriented in one direction – that supports super speed USB as well as can also transmit DisplayPort video, called “DisplayPort Alt Mode.”
  • DisplayPort cables are much simpler to deal with because there is just one type, whereas there are multiple HDMI cables with different capabilities and older types may not be adequately labeled to identify them.
  • The DisplayPort protocol is supported by the WiGig standard, which means that it will allow devices to stream HDCP 2.0-compliant uncompressed videos wirelessly to display monitors, HDTV, wireless storage device, etc., at speeds up to 7 Gbps while operating on the unlicensed 60 GHz spectrum.
  • DisplayPort3 supports up to 5K/60Hz displays through a single cable without compression.
  • DisplayPort3 supports a single-link bandwidth rate of 8.1 Gbps, up to a four-lane total bandwidth of 32.4 Gbps at 60Hz, which can support up to 8K/60Hz (7680×2160) at 4:2:0 and is a 50% increase in bandwidth. It has a final video data rate of 25.92 Gbps after taking encoding overhead into account.
  • DisplayPort3 also supports the new High Bit Rate 3 (HBR3) link rate, and with this it is possible to connect many monitors of different makes, models, resolutions, and refresh rates on each cable. High bit rate DisplayPort cables can support one 4K image or four 1080P images.
  • DisplayPort allows for daisy-chaining several monitors together for a single source, which they call Multi-Stream Transport (MST). It is aimed at desktop applications, but has too many limitations to be considered a viable video wall driver.

For the consumer electronics market, DisplayPort 1.3 included AdaptiveSync, which is meant to enhance gaming action and video playback through active frame rate control, providing smoother and better-quality images, as well as achieving higher color quality in low color resolution display panels. It also allows seamless reduction in the display refresh rate, lowering system power and extending battery life.

One more thing you should be aware of, for interoperability’s sake DisplayPort supports DisplayPort-to-HDMI 2.0 conversion and HDCP 2.2, however, only up to 1080p. They call this DisplayPort dual mode or DP++, which allows HDMI to be outputted from DisplayPort sources via a passive converter cable or adaptor. It also fixed the previous failures of CEC functionality, allowing DisplayPort devices to issue commands to HDMI devices.

HDMI

HDMI was developed by a consortium of electronics companies – Hitachi, Panasonic, Philips, Silicon Image, Sony, and Toshiba – to replace the S-Video, Component and Composite ports that used to be found on video cards, and is now owned by Silicon Image. HDMI 1.0 was released in December 2002, a full eight years before DisplayPort, and was quickly adopted into most CableTV set-top boxes and A/V receivers, especially after they adopted support for high resolution audio in May 2004 with version 1.1.

HDMI 1.2, released in August 2005, was intended to go up against DisplayPort in the PC market; the format war had begun. Along with the updated spec, they released the HDMI Type-A connector for PC sources and delivered a true one-cable solution for all current HD video and audio sources, including they enabled use of native RGB for PCs with optional support of YCbCr for consumer electronics,. Version 1.2a, released in December that same year, made HDMI Consumer Electronic Control (CEC) compliant, promising “smart interoperability” between components, meaning that HDMI devices can issue commands to other HDMI devices. Unfortunately it wasn’t carried out as well as it could have been, as manufacturers made products that only interfaced within their own brands, defeating the purpose.

HDMI 1.3, released in January 2006, increased the ability to transfer data at up to 10.2 Gbps over single-link, increased color support up to 16-bits (“Deep Color”) per channel, added support for xvYCC color space (in addition to sRGB and YCbCr), added automatic audio “lip” syncing capability, and a a new Type C “mini” connector was released for certain devices such as camcorders. For audio, 1.3 added support for Dolby TrueHD, a lossless multi-channel audio codec developed by Dolby Labs used in Blu-ray Disc players and A/V receivers, and DTS-HD Master Audio, a competitive a lossless codec from DTS.

While it may seem that increasing transfer speed to 10.2 Gbps was a good thing, at the time it was already nearly impossible to get a passive copper HDMI cable to pass 1080P further than 15 meters (50 feet). With the addition of Deep Color, distance shrank to less than 6 meters (20 feet). Active cables, such as Opticomm-EMCORE’s HDMI-Fiber hybrid cable, AFC-HDMI2, came out to alleviate this problem, extending distance up to 100 meters (330 feet) while supporting 4K/UHD, 3D, Deep Color, EDID and HDCP. Active copper cables use one or more semiconductor chips to boost performance of the cable, allowing it to be more compact, thinner, longer, and transmit data faster than passive cables.

In May 2009, HDMI 1.4 was released to accommodate 4K/30Hz resolutions but did not increase bandwidth requirements, which was a good thing. It did, however, include several important enhancements, including support for Ethernet-over-HDMI, which eliminated the need for a separate Ethernet cable, Audio Return Channel (ARC) for bi-directional audio, which meant that an HDMI-connected TV could send audio to a sound system thus eliminating a separate audio cable, support for 3D, increased color support up to 12-bit 4:2:2, added support for photographic and computer color spaces sYCC601, AdobeRGB, and AdobeYCC601, which makes HDMI a viable connector on cameras and computers, and introduced a new HDMI micro connector for mobile phones and other portable devices, but only up to 1080P.

In September 2013, HDMI 2.0 was released to accommodate 4K/60Hz resolutions by increasing the ability to transfer data at up to 18 Gbps, however, they kept the same bandwidth frequency of 1.485 GHz by decreasing support for color depth, down to 8-bit 4:2:0. HDMI 2.0 does have the ability to carry increased color depth, but at 12-bit 4:2:2 bandwidth requirements increase up to 2.97 GHz, and at 12-bit 4:4:4 it doubles from 8.9 Gbps to 18 Gbps, and can even go as high as 26 Gbps.

HDMI 2.0 expanded CEC control to up to 15 devices with one remote; in essence operating as a stand-in for a proper universal remote with no lengthy setup. However, as noted previously, it is manufacturers that have held back the true potential of CEC, so we all need to embrace the standard and help people know it exists for it to really take off.

For audiophiles, HDMI 2.0 increased uncompressed audio channel support to 32 (for comparison, Dolby Labs and DTS can both deliver 64 channels of audio currently), including simultaneous delivery of multi-channel streaming audio for up to 4 users, as well as increased audio sample rate to 1536 kHz, meaning that in a full 32-channel system you’d get 48 KHz per channel. They also included automatic audio “lip” syncing capability.

One of the most fascinating aspects of HDMI 2.0 is that it has enough bandwidth, at 18 Gbps, to support the delivery of two different high bit-rate 1080P video streams with audio, coming from a single source such as a cable TV box, to the same screen. Dual view was originally designed to send multiple video streams to a display so that they can be rendered in 3D, for which they increased the frame rate to 25 fps. What they discovered is that it also means that two people could be watching separate different TV channels, or one could be gaming while the other watches TV, at the same time on the same screen, so long as their viewing angles were different.

HDMI 2.0a, released in April 2015, updated the HDMI 2.0 specification to support High Dynamic Range (HDR), which increases display contrast so that the viewer sees a more sharply defined, vibrant image. This means whiter whites, blacker blacks, and better management of compression, all ideal for streaming television over constricted internet bandwidths. It also requires compatible TVs, source devices and specialized content.

The advantages of HDMI for commercial customers include:

  • HDMI carries several signals that DisplayPort does not or is optional to carry, including audio, control signals, which allow the user to unify several pieces of equipment under a single controller, Ethernet data, and Audio Return Channel (ARC).
  • The increase of data transfer speed to 18 Gbps allows HDMI to be used for all applications previously requiring dual-link DVI or DisplayPort (although still less than DisplayPort 1.3 at 32.4 Gbps).
  • HDR display is a pretty significant advancement with highly visible results, and it may play a part in 4K consumer adoption. In professional rendering circles it is far more a necessity than a nice-to-have, for that kind of work. It’s quite possible we will see this taken up by DisplayPort soon as well.
  • With HDBaseT’s ability to deliver HDMI content up to 100 meters (330 ft), distance limitations of HDMI can be avoided, RJ-45 connectors are more secure, CATx cable is more easily terminated in the field and are shielded and less prone to interference.
  • While dual video streams to the same screen might seem like just a cool thing to have, where this can come in handy is that it can cut the number of cable runs in half for some installations. Imagine there are two displays in a bar, fed by a single source in a back room. You can run a cable to each display or, with dual view, a single cable could be run close to the displays then a splitter divides the streams and sends them the rest of the way over two short HDMI cables.

One thing to be aware of with HDMI 2.0 is that it uses HDCP 2.2, which is a different technology than HDCP 1.x and isn’t backward compatible. Also, note that when manufacturers release HDMI 2.0 firmware upgrades for their products, it will necessarily only include a partial feature set, because the hardware itself has limited bandwidth. Firmware upgrades will likely support 4K/60Hz with a reduced 4:2:0 color depth, maxing out the 300 MHz bandwidth available using HDMI 1.4 chips.

Cabling

HDMI 2.0 provides the 18 Gbps bandwidth required for 10-bit and 12-bit color at 4K/60Hz, and DisplayPort 1.3 handles up to 32.4 Gbps in its full four-lane implementation, at which point cabling becomes the bigger challenge for distribution.

Cables designed for HDMI 1.4 systems will work just fine with HDMI 2.0 devices. Most experts recommend you don’t waste money on expensive HDMI cables because there is virtually no difference in the picture quality they produce. However, you do want to consider is distance, where the cables are being installed and the application.

As with HDMI, more expensive DisplayPort cables does not necessarily mean better either, so just make sure your cable is DisplayPort-certified. You may also require a mini-DisplayPort (mDP) connector that fits into Thunderbolt and Apple products, a dual-mode DisplayPort-to-HDMI (DP2HDS) adapter for HDMI displays or, if you have an older VGA display, a DisplayPort-to-VGA (DP2VGA) adaptor.

Conclusion

The Pro A/V industry often looks to connectivity standards implemented by the IT industry, particularly as the AV-IT integration continues to bring about change in ownership of projects. Digital signage and projectors are typically driven by laptops, where for a long time HDMI had a strong installed base, but now DisplayPort is making a strong foothold in the PC space.

While we may continue to struggle with DisplayPort and HDMI vying for dominance in video/audio display and distribution, creating format wars over their various feature sets, ultimately the winners are the users who are able to tap the true potential of 4K/UHD consumer and commercial systems.

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Topics: Important Things to Consider

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