02.11.15

HD and Beyond: Compression is Not a Dirty Word

HDConnectivityNov15

Come along with me as we take a trip back in time.

As we step out of our fictional time-traveling device (I imagine it is bluish and rectangular in a non-copyright-infringing manner), we bear witness to a chilly morning in late 2002. A marching band is tuning up, televisions are being hung, and people are waving signs. It looks like we’ve arrived just in time to witness the dawn of the High-Definition Multimedia Interface. The flags are waving; the standards have flown. I can admit that my recollection of that day is hazy at best, but the result was the same: HDMI entered the world of video transmission. High-definition video, copy-protection, control, power, Ethernet, and Hot Plug detection on 19 pins.

Since then, the HDMI specification has played a major part in driving the Audio/Video industry to where we are today. HDMI has done this by becoming the common language. With HDMI, the Blu-ray player from Manufacturer A can talk to the Audio/Video Receiver from Manufacturer B, which can also talk to the television from Manufacturer C. HDMI as a standard has simplified consumers’ confusion by guaranteeing interoperability of devices.

hdmi-shoes-400x300Heading back to 2015, it is hard to find a device without an HDMI port on it. Televisions, projectors, media players, computers, even SHOES have joined in. For many manufacturers, the decision to include an HDMI port on your new video device is simple: follow the standard or fall by the wayside. In return for our loyalty, HDMI has released the updated 2.0 spec: UltraHD resolution, High Dynamic Range, improved color space and more to come. All of these features over a single copper cable capable of 18 Gigabits per second (Gbps).

The IT Administrator in me immediately stirs. 18 Gigabits per second! On copper? Gasp! That’s quite impressive, and this HDMI cord is so small. 18 Gbps typically requires optical fiber or a massive gauge for copper. This cable rivals some of the strongest cable standards we have in the networking industry. Now here’s where the title of this article starts to make sense. In the video distribution world, bandwidth is everything. An HDMI cable carries a lot of bandwidth, but it can only do so over short distances. In order to go longer distances – we will define “longer” as greater than 15 meters – you have to change cables. There are several options on the market, but none that support 18 Gbps without costing an arm and a leg.

So how do you get an 18Gbps signal onto a cable that can only carry 1Gbps? Compression. Wikipedia – our generation’s encyclopedia – describes compression as “encoding information using fewer bits than the original representation.” Lossy compression is imperfect; it removes information deemed unnecessary, which can result in lower quality. The mainstream meaning of “compression” has become associated with this definition. But there is another kind of compression. Lossless compression is perfect; every bit of information is preserved. For an example, imagine a simple text file with the word “dog” written 200 times. There are 600 characters in that dog file. A compression algorithm turns that text file into “dog*200”, turning 600 characters into 7 characters. On the other end, that file decompresses back to 600 characters in lossless quality without a single lost dog. This is a simple example of course, but shows the power of a good lossless compression algorithm.

Compression is common nowadays. Cable and satellite are compressed. Streaming video services are compressed. Blu-ray discs are compressed. Even the available 4K movie players are playing compressed video. If you don’t believe me, do the bandwidth math on a 2-hour-long, 50GB UltraHD movie file (Hint: it is less than 1/10th of 1 Gbps). If you refuse to watch compression, then you don’t get to watch TV anymore. As technology moves forward, HDMI stays the same. That is the purpose of a standard: to provide stability. It has been 13 years since HDMI was revealed and in that time newer and better video formats have emerged. They each handle video in their own way – some proprietary, some open source – but each must decompress back to HDMI for delivery. That 18 Gbps HDMI signal could only be a fraction of the size in a new compression format while still containing 100% of the video quality provided by the original HDMI signal. I aim to change the mainstream definition of compression. I hereby declare that compression is no longer a dirty word. Audio, video, text, photos, and even financial data must be compressed at one point or another, and everybody would have a fit if their financial data was missing a zero after that data was decompressed. “Is it compressed?” is officially the wrong question.

Eric Martin is senior systems engineer for Just Add Power.