June 2010
Digital video on the desktop – part 1
A history lesson
Before the age of digital media, distribution of a video programme had been quite straightforward for many decades. Everyone could watch a VHS tape at home or in the office, and otherwise, in some corporate environments, a U-matic tape would do the trick. The required players were omnipresent, but had disadvantages. They were mechanical, had spinning heads that accumulated dust, and tape was not the most robust format. The analogue nature of the recorded signal lead to degradation of the picture quality over time and the video was susceptible to tape imperfections and dirt.
Then came the optical Compact Disc: first intended to be an audio-only carrier, but within a decade also used to store computer data (CD-ROM). For video, the storage capacity of a CD was too small, barely enough for a few minutes of video. But with the advent of MPEG-1, one of the first globally standardized video compression methods, it was suddenly possible to reduce the file size of a video significantly, and store a full hour of video onto a CD, in an acceptable VHS-like quality. It was much cheaper and easier to handle than the LaserDisc, which was in a sense the predecessor to the CD; it was a large optical disc, used to store video, but only mildly successful in some niche markets like computer based training.
For feature films, an hour was insufficient so several discs had to be used. That was one of the reasons why the distribution of films on CD-video was not a success, except in some Asian markets. It was only when the DVD was introduced, with at least six times the capacity of a CD and a higher quality compression method (MPEG-2), that the distribution of films on disc really took off.
The DVD-video as we know it, had two successors fighting for the throne: HD-DVD and Blu-ray, both offering a much higher capacity and an improved picture quality (HD - High Definition). After a two year battle, HD-DVD cut its losses and disappeared from the market. Blu-ray won, but now has to face stiff competition from film distribution via the internet.
What CD-video, DVD-video and Blu-ray disc have in common, is that each format was well standardized and played flawlessly on players and recorders from numerous brands. Each format could easily be mass-duplicated and distributed without worrying about compatibility issues.
Meanwhile on the desktop…
For a long time, computers and video belonged to two different worlds. Video was analogue in nature, computers were digital – only being able to calculate and store binary numbers, composed of 0 and 1. Even when the analogue video was converted to a digital format (via analogue to digital converters or ADC’s), the video files took so much space and required so much processing power, that computers simply couldn’t cope – or were too expensive for a wider public.
As years went by, computers became faster and disk storage capacity exploded, doing away with most of the obstacles. Still, even today, PC’s that handle raw, uncompressed video in high (HD) quality are expensive.
To make PC’s more video-friendly – and not only PC’s, but also most digital camcorders – it was clear that uncompressed video was too much to handle comfortably and that some form of compression was needed to reduce the required file size. Several methods were devised, but of the early compression schemes, MPEG-1 quickly surfaced for general use.
Initially, even this compressed format required a plug-in board in the PC to cope with the computing requirements. But as computers became faster, software decoders were able to replace the hardware boards. An avalanche of different compression codecs (coders/decoders) invaded the desktop: Indeo, Cinepac, RealVideo, MPEG-1, MPEG-2, MPEG-4, VP6, DV, H.263, JPEG-2000, DivX, WMV, MPEG-4 AVC (H.264) and then some, with many variants. To make it even more complex and confusing, these codecs are embedded in different “containers” or “wrappers” like AVI, Quicktime, FLV, DMF or MXF. More on that later on.
In short, exchanging video files that are meant to be seen on a computer desktop or laptop can be a bumpy ride. Even if you think your Media Player will play an AVI file, you might end up with a black screen because the codec that was used to compress the video is missing on your system.
To add to the complexity, many people confuse the traditional “video carriers” used in the living room or board room with the “data carriers” used in a computer environment. In other words, a DVD-ROM is not the same as a DVD-video, although they look the same and are recorded in a similar manner.
A DVD-video is a well-defined video storage format with a standardized directory structure and a specific type of video files, while a DVD-ROM is a data storage medium that can hold any type of file: Word documents, PDF’s, spreadsheets, databases, and even… video.
But DVD-ROM has no specification of what a video file should be like, which codec should be used, which container, which data rate, and so on. On such a data disc (CD-ROM, DVD-ROM, BD-ROM and all the writeable and erasable variants), the only characteristic is that you can fill the space with whatever data in whatever format you like. It doesn’t “play” in a DVD player and it doesn’t present a menu when you insert it.
Similarly, if you insert a DVD-video in a PC, it doesn’t know what to do with it, UNLESS you have a program on your system that mimics a DVD player – this is done by software such as PowerDVD or WinDVD, or by media components of recent versions of Windows and Macs.
In part 2 of this series, we will look at the nature of video and the basics of video compression.