Yesterday Apple introduced HD TV downloads to the iTunes store, meaning you can watch Peter be super emo on Heroes at a crispy 720p resolution. That's a higher resolution than DVD, and technically, yup, that's HD. There's a catch though. Like every other video download service touting HD videos, it's all actually lower quality than DVD.
It's all about bitrate: How much data is packed into a file, described as bits per second. Generally speaking, a higher bitrate translates into higher quality audio and video, though quality can also be affected by codec—the encoding and compression technique that was used to make and read the file—so bitrate is not an absolute mark of quality, but it's still a very good indicator.
You're probably most familiar with this bitrate business when it comes to ripping your CDs. When you shove a CD into your computer, your ripping program will ask what format you want and what bitrate you want. A song ripped at a higher bitrate will sound better, with more presence and detail, but it does take up more space.
The same principle applies with video, though it's actually a bigger deal, because it's easier to see quality differences in video than it is to hear differences in audio. The bits make a huge difference when you get into fast moving stuff like sports or action movies—to be frank, they'll look like splattered, smeared shit in highly compressed low-bitrate vids. This chart below, expertly crafted by George Ou at ZDNet provides a solid starting point for comparison, with average bitrates of most digital video available.
As you can see, regular DVD runs at about 6-8 megabits per second. High-def iTunes content, despite having a higher resolution, is half that, a mere 4Mbps. Vudu's current HD movies is also about 4Mbps, if you've got the pipes. Xbox Live Marketplace has the highest bitrate—and indeed, often gets props for its quality—at close to 6.8Mbps. On the other hand, standard-def movies on the Netflix Roku box max out at around 2.2Mbps—and are often delivered in lower qualities because of bandwidth constraints. iTunes standard def TV shows run around 1.5Mbps. Now, consider that Blu-ray is a mean 40Mbps and you see that the definition of "HD" is suddenly remarkably vague.
That's a pissload of numbers. What does that mean?
This comparison test we ran in February pretty much shows you what's wrong: No matter how awesome MPEG-4 compression—or whatever the codec of the month is—gets, it can't work miracles when it's missing bits. It's why Vudu, for instance, is testing out a new closer-to-real-HD service—that they've revealed to us has three times the bitrate of any other download service on the market, meaning it should be close to 20Mbps—that will take hours to deliver to your home. But even then, the notion that it would truly rival Blu-ray is totally laughable.
It's not just download services giving you this watered-down so-called "HD lite", either. Comcast was busted cramming three HD channels into the space of two, resulting in crappy looking HDTV, and the satellite guys adding a million HD channels a year aren't much better.
Now that you understand what makes or breaks an HD picture—the amount of data— it's probably no surprise to you that the major reason everyone is peddling subpar HD is bandwidth. HD content is pipe-bustingly huge—a standard-def Battlestar Galactica file on iTunes is 520MB and takes about 15 minutes to download via a strong cable connection. The 720p HD download is 1.4GB and takes 40 minutes or so for your hard drive to completely swallow. The Blu-ray version of the same ep might be 10 times that—like 14GB. Putting that in more context, a single TV episode would take up twice the space as the average dual-layer DVD movie.
Right now, we don't have the broadband infrastructure to support it, and who knows when we will? Hell, the people with the best chance of giving us that added bandwidth—the major ISPs like Comcast and AT&T—are doing just the opposite: Implementing usage caps that will mean less HD downloading. The sad thing is, they probably won't even use the added bandwidth to make their own HD TV channels look better.