When we asked our faithful readers what technological advances had made the biggest difference to their lives, Prospero424 stepped up to the plate to deliver a humdinger: video compression.

To Prospero, MPEG-4 part 2 compression was "when the internet truly became a viable A/V platform/medium. This is when storing hours of video that looked good enough to watch and keep became viable to store online locally (i.e. on your hard disks, not on external discs, etc.) on personal computers. No other single aspect of the evolution of entertainment has done more to change how I consume it."

Let's rewind the tape a little bit further than that, in order to see the breaking point arrive. Prospero is correct that video compression has indeed revolutionized entertainment over the past decade, but the technology has a longer history than you might think.

The rise of efficient compression

Intel's Indeo codec was popular back in the day

The carousel of progress keeps on turning, and today's compression algorithms are much more effective than older ones. The Cinepak codec that powered early versions of both QuickTime and Windows Media video formats aimed no higher than getting 320x240 video resolution out of a standard CD-ROM drive, which means cramming 2.2Mbps plus audio and overhead into a 1.2Mbps traffic stream. Call it 50 percent compression on a good day.

If you never saw a digital video back in the 1990s, you're not alone. The files were large and the downloads were slow. And while the tiny hard drives of the era would have welcomed some video compression with open arms, the other parts of that equation were simply not there; an Intel 486 or Pentium would grind to a standstill trying to make sense of a simplistic Motion JPEG or MPEG-1 video, even at very low resolutions. But better days were just around the corner.

The popular MPEG-2 standard pretty much destroyed Cinepak, Intel Indeo, and other early codecs in the late 1990s by compressing video streams to as much as 1/30 of the original video size while still maintaining acceptable picture quality. That's hefty enough to let that old 1x CD-ROM handle a full, standard-resolution NTSC signal at about 1Mbps. This is the format used in DVD video, many digital broadcasts, and most online video streams.

MPEG-2 can present a 1080p video in a 2Mbps envelope, but with horrible blocking artifacts from all the compression if you take it that far. These codecs are lossy, which means that you must always balance image quality against file size. HD video was not exactly what MPEG-2 was made for.

By the standards of modern hardware, like recent models of Texas Instruments' OMAP processors and anything from Intel or AMD, MPEG-2 encoding is a walk in the park. Newer formats, not so much. This is why your TiVo box still stores DVR recordings in this age-old format.

A TiVo Series 3 can play H.264 video (more on those later), but does not have the muscle to make its own, so you're stuck converting your videos elsewhere and sending them back to the TiVo again if you're hell bent on making the most of your hard drive. Since MPEG-2 videos can fill up a DVR in short order, many of us opt to simply hook up an external hard drive to the set-top box instead-—or roll our own home theater systems.

But we wouldn't use MPEG-2 for that, now would we?

And then comes the MPEG-4 Part 2 format, more commonly known under the names of codec implementations like Xvid, DivX, 3ivx, or the QuickTime 6 version. Like MPEG-2 before it, MPEG-4/2 quickly caught on thanks to another step up in compression quality—the same video at comparable levels of picture quality will use about half the bandwidth of MPEG-2 when presented with an MPEG-4 Part 2 codec.

The rise of Xvid, DivX 3.11a, 3ivx, and others came at a time when broadband Internet service was coming into its own in the US, and along with the relentless march of technological advances in fields like hard drive storage and CPU power, digital video took off like a rocket.

File sharing sites like KaZaA, IMesh, and Gnutella made it easy to find and download video files. The small size and high quality of MPEG-4 Part 2 codecs made the format perfect for downloading, and the format quickly became ubiquitous. You could find full movies on file sharing networks before their theatrical premieres, and DVD rips before the discs hit store shelves—all at glorious full NTSC or better display resolutions.

In 2001, your desktop computer could sport gigahertz bragging rights on a Coppermine Pentium III or Palomino Athlon. These chips still needed help from your Radeon or GeForce to handle full-screen DVD playback, but they were powerful enough to pick apart MPEG-2 videos in smaller sizes. These machines were ready and able to fill up their massive 100GB hard drives with videos.

And the MPEG-4 Part 2 gravy train kept on rolling for years. When it comes to video encoders for personal use, it was the king of the hill from the early 2000s, and arguably still is. This is probably what you'd use for a hand-rolled media server today, running Windows Media Center, SageTV, Boxee, or MythTV.

MPEG-4 video is, as Prospero noted, compressed enough to let you store and enjoy media in a plethora of new ways. Filling up a couple hundred gigabytes of hard drive space takes much longer with efficient compression, and a full-length movie often weighs in at less than 1GB. That's a mental barrier for many people, drawing a line in the sand between "huge" and "reasonable" files.

While the Apple iPhone and iPod lines don't support Divx-compatible formats directly, they can decode the equally efficient recent versions of QuickTime media and there are plenty of converters between the formats. And I'm not an iPhone addict, but I bet there's an app for MPEG-4 Part 2 playback. Handheld media gadgets based on Windows Media or Android platforms have their ways of handling high-quality video streams too, which makes them useful for playing your own videos or streaming shows across WiFi or 3G connections. Mobile video would simply not be possible or palatable if not for compression techniques of the MPEG-4 magnitude.

But nothing lasts forever.