Audio Tech

FAQ > Home Theater FAQ > Q. What's with all the versions of HDMI?

HDMI v1.0 was the original format, released in December 2002. It took DVI's video signal format and added in the ability to carry a Dolby Digital or DTS bitstream or only two channels of PCM audio (48kHz, 24-bit). The two-channel PCM restriction worked fine for connections between cable/satellite receivers or DVD players and a stand-alone HDTV (which only supported two channels of audio) but it wouldn't be able to support the new audio formats that were slated to accompany HD optical discs (HD-DVD and Blu-ray). Adoption of HDMI v1.0 was sluggish, as DVI-HDCP had a headstart in the market. It didn't help that HDMI shares DVI's cable length restriction – anything more than about 15 meters violates the specification and is likely to require either a booster or a conversion to fiber optic.

2. Version 1.1

It was with Version 1.1 (released in May 2004) that HDMI was finally able to make a compelling argument for superceding DVI-HDCP. HDMI could now carry multichannel PCM audio (eight channels at 192kHz, 24-bit) in addition to Dolby Digital and DTS compressed bitstreams. Version 1.1 also added support for passing the bitstream data from DVD-Audio discs, which previously had to be decoded inside the player and output as six channels of analog or passed as a bitstream through IEEE-1394 (also called FireWire or iLink, a connection type that never saw widespread adoption).

3. Version 1.2

HDMI v1.2 was adopted in August 2005 (v1.2a was adopted in December 2005 and added some testing and certification language). The only notable difference between it and v1.1 is support for a DSD (one bit audio) digital bitstream. This means that a player can now send the raw digital signal from an SACD over HDMI to a receiver or processor, eliminating the need for decoding of the DSD signal at the player.

4. Version 1.3

When I initially wrote this HDMI FAQ in early June 2006, I didn't expect to see HDMI release the v1.3 spec before September 2006. Lo and behold, they announced the completion of the spec in mid-June and had officially adopted it by June 22, 2006. We knew that we were getting bitstream support for Dolby Digital Plus, Dolby TrueHD, and DTS-HD, but there's a lot more to the v1.3 spec than that sought-after change. This addition allows HD-DVD and Blu-ray players to mimic the DVD player's ability to serve solely as a transport (no audio decoding capabilities required), and would once again put all signal decoding and processing in the receiver or surround processor. Doing this will reportedly have some detrimental effects on interactive content for both formats: when the HD-DVD or Blu-ray player handles the decoding (as is the case with v1.1 and v1.2) it will be possible for the player to retrieve streaming Internet content (such as new commentary tracks) and integrate it with the decoded multichannel PCM that is sent to the reciever. That will not be possible when the raw bitstream is output to the receiver.

Surprisingly, the addition of bitstream support for HD audio formats wasn't the central change. The main change to HDMI with v1.3 is the video bandwidth, which increases from 165MHz to 340MHz (10.2Gbps). This change allows HDMI to carry video signals with 30-bit, 36-bit, or 48-bit color depths (previous versions were limited to 24-bit color depth). It's interesting to note how this appears to have been accomplished. HDMI's video side was originally based on DVI, but it only used DVI's single-link video connection – it disregarded the dual-link arrangement that allowed DVI to handle extremely high resolution computer monitors (up to 2048 x 1536 compared to single-link's maximum resolution of 1920 x 1080). Using the single-link connection provided them with 165MHz of bandwidth, or a maximum resolution of 1080p (the maximum resolution used by HDTV's). In v1.3, they've added support for dual-link, which is how the bandwidth was able to increase to 340MHz. Accompanying this change is the addition of “xvYCC” color space, which supports 1.8 times as many colors as existing HDTV signals. Another unexpected addition was an automatic audio/video sync capability that compensates for the video signal delays introduced by modern video processing. Lastly, the expected changes to the connector (to address complaints about how easy it is for HDMI connectors to be pulled out or to fall out due to the weight of the cable) did not appear in v1.3. Instead, an optional mini-connector was added for use with HD camcorders and still cameras.

The arrival of HDMI v1.3 will hopefully allow the format to solidify long enough for manufacturers to integrate it into components with long life cycles (such as surround sound processors) and remove some of the uncertainty from the new HD optical disc formats' players. It appears that the early arrival of the new version is due to Sony's desire to include it in the Playstation3, which will be arriving in November 2006. The PS3 will probably be the first or one of the first products to include HDMI v1.3; it'll likely be 2007 before many other products start including it.

Update - August 30, 2007: The HDMI v1.3 spec has been official for roughly a year now. It took nearly six months for the first HDMI v1.3 sources to appear (the Playstation3), close to a full year to see the first HDMI v1.3 receivers, and we're just now starting to see announcements for HDMI v1.3 displays. During that year, we've learned a few things that are worth looking at. Let's look at a few of these new features:

Bitstream output for Dolby Digital Plus, Dolby TrueHD, and DTS-HD (Updated May 8, 2009): For well over a year before HDMI v1.3 arrived, this was the feature that led consumers to demand hardware supporting v1.3. The idea of returning to the approach used with Dolby Digital and DTS (of decoding the multichannel audio signals in the receiver rather than in each source) seemed very powerful. Once HDMI v1.3 arrived in hardware, everyone assumed that this bitstream support existed. It turns out that there are a couple issues there, though. First, the initial generation of HDMI v1.3 transmitter chips (used in Sony's Playstation3, Samsung's BD-P1200, and some Toshiba HD-DVD players) can't support these bitstreams, making it impossible for the first generation of HDMI v1.3 devices to output a DD+, TrueHD, or DTS-HD Master Audio bitstream. It was not until late in 2007 that we finally saw HDMI v1.3 gear that supported bitstreaming (Panasonic's BD30 Blu-ray player was the first product I knew of that offered this, and it was released in late October 2007). Once we had that, however, it brought us to the second issue. Even when hardware supports bitstream output, will we have any software that allows it? Both HD-DVD and Blu-ray offer an array of new interactive content, although so far HD-DVD's been more successful in implementing it in player hardware. Some of this new content includes interactive menus (disc menus that are overlayed on top of the movie, so you can jump to a different scene or select a commentary track without leaving the program), picture-in-picture, and Internet connectivity for things like streaming additional commentary tracks. Many of these require more than one audio stream to be mixed together (a simple example being sound effects in the disc menu that play without interrupting the movie soundtrack). For those multi-stream features to work, the player must decode the main soundtrack bitstream internally so that the mixing can be done with raw PCM data. As a result, these features make a bitstream output impossible. I've read reports ever since the format launched indicating that HD-DVD discs are being mastered with settings that force the player to decode internally in order to make sure the interactive content works properly, which makes hardware support for bitstream output irrelevent for HD-DVD players. Blu-ray is less restrictive, however, and bitstream-compatible players typically include a setting to control secondary audio. That setting must be set to "off" (disabling any features on discs that offer secondary audio for menus or for mixing audio tracks on bonus features such as commentary tracks) in order to allow bitstream output.
Automatic lip sync adjustment: One feature that is mentioned from time to time is automatic lip sync adjustment. The HDMI v1.3 spec allows for components to communicate with each other to track the amount of video signal delay introduced by video processing (deinterlacing or scaling) and apply a delay to the audio signal to keep the two synchronized. The catch to this that is not widely mentioned is that this only works if the entire signal path (source component, surround sound receiver or processor, and display) is HDMI v1.3 compliant and includes support for this feature. As we learned from the fact that the initial HDMI v1.3 sources couldn't output a bitstream due to hardware limitations, the v1.3 spec doesn't require that all v1.3 features be implemented in a device.
Consumer Electronics Control (CEC): This is another optional feature, which companies are implementing under different names – to the point that each company has their own name for the feature. The idea is that the components can be integrated and operate more seemlessly: for example, turning the player on could issue commands via CEC to make sure the other components are also on and set to the correct inputs. The reality is that each company's implementation may be somewhat different, not all HDMI v1.3 products implement any form of CEC, and the whole thing just doesn't work yet. Eventually, it may work, but there is currently not enough of a concrete standard for any equipment to be developed to use CEC reliably.

Clearly, the arrival of HDMI v1.3 has not been the key to industry-wide realization of the interface's full potential. Mostly, it's just sustained the existing level of consumer confusion and made life a little bit harder for equipment manufacturers who are trying to develop new hardware with HDMI capability. It doesn't help that we've seen two small revisions (HDMI v1.3a and HDMI v1.3b). HDMI v1.3a included a number of adjustments to the spec (including several related to CEC) when released in November 2006. HDMI v1.3b is a testing specification that was released in March 2007.

5. Version 1.4

(Added May 7, 2009) It's been a couple of years since we had to worry about significant new changes to the HDMI spec. HDMI v1.3 hardware has become much more common, thanks in part to Blu-ray (and the end of the format war between it and HD-DVD). We still have regular issues with HDCP handshaking, but at least CEC has stabilized from the early implementations (so you are no longer likely to encounter inexplicable control problems when mixing different manufacturers' unique implementations of CEC). That means it's time for a new HDMI version to emerge – we don't needone, but I'm not sure the HDMI cares and I am beginning to think that they are somehow uncomfortable with allowing the standard to ever be properly mature (even though they should be focused specifically on that as a primary objective). So what will HDMI v1.4 add?

Networking: HDMI v1.4 will allow for the incorporation of an Ethernet connection into the HDMI cable, alongside the existing audio and video.
Audio Return Channel: HDMI v1.4 will add a second audio path (equivalent to an SPDIF coaxial or optical digital audio cable). This will allow a connection between surround receiver and HDTV to carry PCM stereo, Dolby Digital, or DTS from the HDTV to the receiver.
Performance: HDMI v1.4 will support higher resolutions (4kx2k) and 3D, which means increasing the video bandwidth available.
Automotive HDMI: HDMI v1.4 will include a new connector spec that is intended for use by the auto industry so they can incorporate HD video and high-resolution audio into cars.
Smaller Connector: HDMI v1.4 will include a spec for a new, smaller 19-pin connector. The press release does not indicate where this connector will be used, since HDMI v1.3 already added a small connector for use with camcorders.

So what does all of this gain us? The incorporation of a network cable is clearly in response to BD-Live (also called Profile 2.0) and network media servers, but there will still need to be some sort of connection back to a home network to provide a link to the Internet and remote files. How that would work has not been spelled out, but it seems likely that the only way to reduce the small (but growing) number of network cables will be to replace all of your components with HDMI v1.4 gear – and you will still need a wired or wireless link to the local network, which will need to connect to at least one HDMI v1.4 device. The audio return channel will eliminate a single coaxial or optical digital audio cable for people who use their HDTV's over-the-air HD tuner in a surround sound setup, but it will require you to purchase both an HDMI v1.4 receiver and display. That's potentially thousands of dollars invested to remove a very small $15 cable. The increased bandwidth is intended to support two video standards that remain undefined. Several groups are developing 3D video standards, but none have been published yet. And 4k video is still years away from being ready for consumer adoption, with no existing video format available to deliver that resolution to the home. The new connector does not appear to address the biggest issue with the existing connector: the lack of locking. A smaller connector, if it were adopted in place of the existing one, would potentially exascerbate the existing problem of cables pulling connectors loose (fewer pins means less surface area for the connector to have available, which means less weight required to pull it loose). Out of all of these, the only one that seems likely to have a practical benefit to the marketplace is the automotive connector spec.

At present, HDMI v1.4 is not a published specification. It is simply an outline of what the next generation of HDMI is expected to offer. HDMI's January 2009 press release hinted at a mid-2009 launch for this spec, which would suggest that we would not be able to expect to see any HDMI v1.4 hardware prior to mid-2010.

Last updated on May 5, 2011 by Alex Robles