When it comes to digital mass media, there are two factors which remain undisputed: that convenience trumps quality nine times out of ten, and that smaller is better.

Compact Discs were thinner, lighter, and more durable than cassette or vinyl. MP3 is weightless, stateless and (physically) indestructible.

But this isn’t a discussion on “which technology is better”, or about fidelity. CD’s had more bandwidth, but (arguably) sacrificed detail over vinyl. However, you can’t exactly carry a record player on your hip, or play it in a car. Modern MP3s and AACs compress the large bandwidth available on CD’s down to the bare minimum of what is deemed “important” by the perceptual codecs, again sacrificing quality for convenience: but you can’t carry a 500 CD changer on your hip.

But as iPods get thinner, lighter, and smaller, there’s one thing that just keeps on growing: our storage requirements.

When George Lucas was interviewed by Wired in 1997, he said, “If I could wave that magic wand, I guess what I’d love to have is infinite storage.”

Once the media becomes digital, it ceases to occupy physical space, but continues to occupy storage space. And when it comes to the media we consume, that means our storage requirements will grow and grow and grow.

Steve Jobs seems to believe that “People want to own their music. You don’t want to rent your music” which could be interpreted as people want to store their music, and be responsible for it’s storage. The success of the iTunes Music Store seems to be a fair indicator that this is true.

So what does that mean for the typical consumer? How much storage is “enough”? If you want to take your music with you, which iPod are you? How big is big? One gigabyte? Two gigabytes? 30GB? 60GB? More?

Ask most people, and (assuming they are familiar with the term gigabyte) “a couple” is probably what most would respond. It’s not a question that many have considered.

Let’s look at it this way: the average album is 10 songs long, and the average mp3/aac file is 5MB. That’s around 50MB an album.

Assuming an averaging purchasing rate of 5-10 albums per year, the typical consumer would have roughly 1-2.5GB worth of music in their collection by the age of 20 (assuming it’s all been converted), accruing further at a rate of 250-500MB per year.

This seems to be in line with the general sales of portable media devices, whose volumes are weighted towards smaller-capacities. However, the fraction of the market participating in digital downloads is not the same as the average CD album buyer, and so could be a greater consumer of media, justifying the demand for 10, 20, 30 and 60GB players.

I am one of these people. My iTunes Library now stands at a whopping 84GB, with over 8800 items. I can hit play now and not hear the same song twice for over a month.

In answer to the question of which iPod I am, however, is: I am nano. Four gigabytes of Smart Playlist auto-updated music skimmed off the top of my collection (part favorites, part latest-additions, part random).

Now it’s not the fact that even the 60GB iPod won’t hold my collection, it’s the fact that my collection is still growing. I hesitated about jumping onto the 10GB iPod when my collection was 8GB, and about the 40GB when my collection hovered at 36GB. So how did my Library double in size in the past two years?

The answer is simple: video

While we pine for smaller and smaller devices, and more and more efficient codecs to compress our media, our storage requirements continue to grow. There are those who promise that storage is continually getting cheaper, and that it won’t be an issue as time and technology progress. What this does not address are the interface requirements for managing, navigating and interacting with such large quantities of information.

Interfacing with my full artist list of 1300 artists on an iPod is borderline painful. Playlists are the only reasonable way to usefully access the music, unless you want to spin your thumb around the clickwheel until RSI sets in.

Out of my 84GB Library, half is dedicated to video (42GB). Of those 42GB, 38 of them are tv shows. Aha! I hear you say: that’s what it is! 350MB per episode AVI’s… but how did you get them imported to iTunes? :/

Here’s the kicker: these are H.264 encoded videos ready for iPod, compressed to a bitrate of 650kbps (including audio) and 320×180/176 dimension. A typical television episode in this format is 175-180MB in size, and displays at roughly equivalent quality to standard definition television.

At 180MB per episode, we’re talking 250 episodes of television. Where a season of programming is 24 episodes, that’s five seasons, or 4.4GB per season of programming (and conveniently fits on a single-layer DVD).

Let’s compare our video size requirements to our average album purchase from before. We said at an average growth of 5-10 albums per year, a consumer’s library would increase by 250-500MB per year. If this same user follows 1 television series in that entire time, this would add an additional 4.4GB per year to that storage requirement. That means 4.6 to 5.1GB per year (also assuming 320×180 resolution at 650kbps bitrate, which seems unlikely with the advent of HD).

All of a sudden, even a 100GB iPod is starting to look a little short-sighted.