Why Encoding Is Necessary - Bandwidth

You've spent countless hours and quite possibly a sizeable sum of money to produce a broadcast-quality podcast. Now you're being asked to take the polished result and convert it to a different format, which may compromise the quality of the original. Why?

The simple answer is because the raw audio and video files are too large to deliver practically via the Internet. There's no technical reason you can't deliver the original files — but it would take an incredibly long time for the files to download, and your monthly delivery bill would be sky high. To better understand the practical limitations involved, you must understand the concepts of bandwidth and throughput.

Bandwidth
Bandwidth, in the networking sense of the word, is a measurement of the amount of data that is being transmitted at any given point. Throughput is the aggregate amount of bandwidth that has been used over a given time period. Think about water coming out of a faucet: The water can come out slowly or quickly depending on how much you open the tap. A gallon jug fills slowly or quickly depending on how fast the water is coming out. The "bandwidth" of the faucet is the speed of the water coming out; the "throughput" is the total amount of water that comes out.

In podcasting, we come across bandwidth and throughput in a number of different areas. First, each of your potential audience members is connected to the Internet in some way, and that connection has an advertised bandwidth. If they're on DSL or cable modem, they may have a download bandwidth somewhere between 256 kilobits per second (kbps) to several megabits per second (mbps). Similarly, when you upload your podcast to a server or distribution service, you're using bandwidth, but you're uploading, not downloading. The upload or upstream speed of DSL and cable modems is usually far less than the download speed. Regardless of which direction the data is traveling, the bandwidth available determines the speed at which the transfer takes place.

Let's say you've recorded a 20-minute audio podcast. If you've recorded at CD quality, you recorded in stereo, sampling at 44.1kHz, using 16 bits per sample. We can determine how large this file is using some simple math:

44,100 samples/sec * 16 bits/sample * 2 channels = 1,411,200
bits/second
1,411,200 bits/sec / 8 bits/byte = 176,400 bytes/second
176,400 bytes/second / 1024 = 172.3 kilobytes per second (KBps)
172.3 KB/sec * 60 secs/min * 20 min = 206,718.75 KB
206,718.75 / 1024 = Approximately 202 megabytes (MB)

So the raw file is over 200 megabytes. (In fact, you can do this math much more quickly: One minute of stereo CD audio is approximately 10 MB, so 20 * 10 = ∼200 MB.) Let's assume one of your audience members is on a fairly standard DSL line, with a download speed of approximately 500 Kbps. You can calculate the download time with a bit of math. All you have to do is convert the file size from megabytes into kilobits, and then divide by the download speed:

200MB * 8 bits/byte = 1600 megabits
1,600 megabits * 1024 = 1,638,400 kilobits
1,638,400 kilobits / 500 kbps = 3,266 seconds
3,266 seconds / 60 seconds/minute = 54.6 minutes

So your podcast would take just under an hour to download. If the person is downloading in the background, this might not be too much of a problem, but chances are he's checking e-mail, surfing the Web, and doing other things on his computer that might further constrict the available bandwidth, which in turn makes the download take even longer. Additionally, he may not be getting the full bandwidth that he's paying for (see the "Why Does My Broadband Connection Seem Slow?" sidebar). Overall, this is not an optimal experience.

What we want to do is deliver a high-quality podcast that doesn't take hours to download. Encoding software enables us to do precisely this. For example, if we encode the file using an MP3 codec, we can achieve CD quality using only 128 kbps. In this case, our file would be:

128 kbits/sec * 60 seconds/minute * 20 minutes = 153,600 kilobits
153,600 kbits / 8 bits/byte = 19,200 kbytes
19,200 kbytes / 1024 = 18.75 MB

Our file size is less than ten percent of what it was before, and the download time is therefore reduced to about five minutes, which is much more like it. And because each of your listeners is downloading a smaller file, you use much less throughput.

Podcast : Making your choices

Get out a piece of paper. You need about 10 minutes today and 15 minutes tomorrow to complete this exercise. Really, if you just wait a day or two between the phases of this exercise, you'll get a much better program by following this process:

1. Make three columns on the page. Place a heading for the left column, "Topics," and call the middle column "What I can add."

2. Under "Topics," write down five things you think about every day, whether it's a hobby, your business, sports, politics, or something you argue with friends about frequently and energetically — things people enjoy talking with you about. Don't take too long, just a couple minutes. What wakes you up? Are you worried about finances, the state of your relationships? What gets you going?

3. Now, under "What I can add," write the ideas you've had about each of your topics in the past couple of days. These could be your "original notions" about the topic, such as a theory that the Red Sox consistently under-invest in third basemen, that there are three regions of the world or industries that are ripe for investment by people like you seeking improved returns, or maybe your ideas about how to resolve the political problems in the Middle East. You get the idea; write down what, if you were to do a podcast on that topic today, you would talk about. Got it all on paper? Now, stop. Let it percolate.

4. On day 2, return to your worksheet. Add a title to the third column, "Sound." Have you thought of additional topics? Add them to the Topics column. More importantly, as you went about the intervening day, did you find yourself identifying stories in the news, ideas in your head, or things people said to you in conversation that you'd like to have recorded for a podcast? Write these under "Sound" for each of the topics. Seriously, are you already looking for audio as a natural part of your day? That's the producer's habit that we're looking to cultivate, starting with this list. Finally, write down the ideas you'd add about each of the topics or the sound you'd record; that's the raw material of your own comments.

After the second visit, your list probably looks somewhat lopsided. Some of the ideas you had yesterday yielded little or nothing, because they aren't sustainable topics. This is the problem with picking a topic: Unless you genuinely engage with the subject, you'll quickly find yourself experiencing burn-out. Don't be one of the people who launch two or three podcasts on a whim and then fade away. You may want to repeat the exercise for a few days; this is an approach we've used with programs created for a news network staffed by young journalists who needed to work through the difference between what they could talk about and what they really wanted to talk about day-in and day-out on a regular program.

Of the topics you've identified, which produced the most notes? Take a look at the environment for that topic. Begin by doing searches on news and search sites for articles that relate to the topic. You're looking here for how much material you can expect to draw from. Whether you're doing topical political humor or investing ideas, you need fresh material to write about. If the topic doesn't present you with enough subjects to talk about as frequently as you hope to produce, then you need to look again at the list and combine topics or find another more fruitful one.

This exercise also forces you to begin the process of producing the show on paper, making you test your resolve about the topic and the frequency with which you can expect to deliver programs. Even if there is lots of material, you may not find all of it particularly interesting to talk about, so you must start to think through what you're going to do with outside information, especially how you're going to link it to the ideas you want to add — after all, it's your head that people will want to tune into. Make sure you're offering a podcast that accesses the busier parts of your brain. You can discuss your ideas about phenomenology, a branch of philosophy, or global warming, as long as you know you'll be productive and engaging.

Look, if you're contemplating a show for your family, they'll probably want to listen just to hear you. Your family loves you, or at least we hope they do. But if you want to earn the attention of an audience — whether they're your customers or complete strangers — for a long time to come, these are serious questions to ask yourself. Some labor now will save you from totally retooling the show after launch.

Finally, how often should one produce? That answer depends very much on the format and topic you choose. For example, doing news commentary once a week will not keep up with the pace of events, so you'll have difficulty convincing listeners you are timely. Daily may be your only option, unless you decide to focus on some aspect of the news that can be wrapped and summarized less often, such as The Week in Advertising or This Week's Seattle Mariners Moves. A show about history or math, however, that goes into detail about events or concepts can be a weekly or monthly program that is listened to repeatedly in order to get the most out of it.

Frequency is up to you, although you should avoid the temptation to over-deliver. People may not be able to keep up with your production schedule and feel they are falling behind if, at first, you offer a program a day (music programming, where there is no narrative to lose track of, can be daily from the get-go). It's probably best to start with a less frequent production, gather feedback from your listeners, and then decide about increasing how often you deliver new shows. That way, you will not find yourself backing off an original and overly ambitious promise to offer a daily show when it's not what is needed. Or, think of it this way: It is better to add shows — it's like increasing the value — than justify producing less.

Exploring the World of Podcasting

We show you how to find, subscribe, and listen to thousands of podcasts available on the Net. The steps for getting audio files onto your portable audio player, such as an iPod, or burning a CD and listening on a desktop computer are few and easy to understand. We also introduce you to the client software used to subscribe to and download podcasts, including the wide variety available for the Windows, Macintosh, and Linux operating systems.

A variety of podcast portals offer lists of podcasts; we walk you through some of the better neighborhoods in podcastland, explaining the basic mechanics that make podcasting work. Finally, as part of that technical introduction, we explain the technical origins and personal conflicts that color the podcast landscape. After this, if you just want to listen, you're ready to go. But we bet a big bag of fish that, after you've tried listening, you're going to want to start to speak with a podcast of your own.

The Basics of Listening
Listening is easy. Managing your subscriptions is easy. Keeping up with everything you can download with such ease is harder. That's because the listener is in control. Unlike broadcast media, where every listening choice is a zero-sum game, where choosing one program means you can't listen to the others, podcasting gives you the power to stack up a full schedule of listening and more.

First, you need to get an application commonly referred to as a "podcatcher," news reader, or aggregator. All these applications do the same thing; they visit a list of servers to check for newly posted files. A push client was locked to a particular server.

If you had multiple push services, it meant running several different applications. With podcast and RSS, your subscriptions are handled by one application. Later, we introduce you to the choices in podcatchers; here, we focus on what a podcatcher does.

As shown in Figure below, a podcatcher running on your computer maintains a list of subscriptions in the form of uniform resource identifiers (URIs, also called URLs) that tell the application the name of each server and where subscription files are stored on a regular schedule that you specify. Each subscription is referred to as a "feed," which is the Web address of a file that describes the catalog of shows stored in a particular directory on a server. You may have feeds for several different programs on the server, each with a unique URL for the XML file for each show.


The podcatching process

For example, let's say you've subscribed to a podcast called Big Blue's Beer Show, which is stored on a server named http://www.bigblueBeer.com in a file called "podxml.xml." The full address of the file is http://www.bigbluebeer.com/site/feeds/podxml.com, and you've set your podcatcher to visit the site every day at 6:00 AM to check for new shows listed in that XML file. When the application finds a new show listed in the podxml.xml, the full audio file is downloaded to your PC and stored in a directory where you can open it and listen, or the podcatcher application can identify new audio or video files and move it to your computer or portable audio player. The podcatcher then moves to the next subscription on the list, in this case, a http://PodcastBible.com podcast, and checks that server for a new show. At the end of the update process, your podcatcher has a list of programs that are downloaded and ready for listening.

Of course, you can have your podcatcher visit many servers, collecting programs all day long, but remember that audio files take lots of space on the hard drive. An hour of MP3 audio is typically about 30 MB in size. Like a digital video recorder for your television, podcatchers require some tending, with frequent weeding to keep space available for new programs.

Why Podcasting Is Different

The unique thing about podcasting is the flexibility it enables for both producers and the audience. Both producers and audiences enjoy immensely more freedom today than they did in the broadcast schedule. Creative people, whether voice talent, writers, or ordinary people with a passion — about almost anything, from their hobby to the history of their family or a project at work — can find an audience. Even small audiences are eminently reasonable in podcasting, because the costs of producing and delivering programs are so low that any niche interest can be served. We saw the same phenomenon in publishing with the advent of computer desktop publishing, when a flowering of small magazines suddenly appeared to serve incredibly focused markets and newsletters sprouted in every industry and at every company.

Listeners, too, are freed in an important way: The schedule they listen on is in their hands, not controlled by the broadcaster who delivers the shows. Podcasts allow the complete reordering of the listening day, providing users who download programs the ability to start and stop a program at will, to listen at their leisure to programs at any time of the day or night. The result of this bidirectional freedom is a media environment where programming is offered by producers and selected and listened to by people on a fluid schedule and under a far broader range of business models than were possible before. Add to this easy-to-distribute environment the element of portability — a podcast can be loaded onto a variety of portable devices, from MP3 players to wireless telephone handsets — and the location of the listener has been radically transformed. No longer does listening to a program on the Web mean having to be tethered to your computer. Just export the show to your iPod and go.

Thousands, if not millions, of different messages can be delivered through a podcast. What blogs are to the newspapers, podcasts are for radio, deconstructing the strict order of the mass-media marketplace. Where radio and audio production have been rarified professions in the mass media era, the relentless march of Moore's Law has brought the tools and distribution networks that made those mass media expensive to experiment with and compete in to a generation known as podcasters.

Voices make the podcast. For the past 85 years, since commercial radio first appeared, audiences have become accustomed to a narrow range of voices that are "professional," usually deeper than the ordinary speaker and paced like a race or a seduction, but decidedly not like everyone normally speaks. Podcasts break that monopoly. In less than a decade, commercial radio has descended into crisis as audiences flee to the Internet, in the form of streaming and downloadable programming, not to mention the allure of paid commercial-free radio broadcast from satellites in space. Podcasts burst on the scene in late 2004, claiming thousands of listeners in the first few months and millions within a year. Depending on which research firm you believe, between 30 million to 50 million people will be podcast listeners by the end of the decade. The monopoly that was radio is broken, dismantled, kaput.

What Is Podcasting?

Just two years ago, at this writing, the idea of a "podcast" made its first appearance on the scene. Already as many as 10,000 people are podcasting and as many as 15 million listeners are downloading and listening to audio programming through Real Simple Syndication (RSS) channels. Early podcasters are earning a living from their work, while others have launched service businesses that deliver audio production for commercial clients. But for most, the vast majority, podcasting is about one-to-few communication facilitated by IP-based networks and simple tools


The tools of the podcaster's trade

The basics you need to do a podcast: A microphone and recording device, which could be an old tape player, a solid-state recorder, or your personal computer, editing software, and a place to host the resulting program. This sounds like a lot of pieces, but compared to the complexity of producing and distributing a radio or television program a decade ago, podcasting is self-produced media realized. In a nutshell, a podcast is, according to Wikipedia, a "direct download…file, but the subscription feed of automatically delivered new content is what distinguishes a podcast from a simple download or real-time streaming." This is a description of many different services that pre-date the introduction of podcasting; a more accurate definition, in our opinion, is this:

"A podcast is a series of audio (or video) programs delivered through a static URL containing an RSS feed that automatically updates a list of programs on the listener's computer so that people may download new programs using a desktop application. Programs can be delivered to the listener automatically or when they choose to download them."

Already there are variations on this definition, because podcasts can be delivered directly to handheld devices without the intervention of a desktop computer or software. Likewise, podcasts have changed radically as video has been added to the mix. Originally, podcasts were simply MP3 files, a widely used audio format. Today, podcasts include MP4 and other video file formats, as well as other audio formats such as Windows Media, Ogg Vorbis, and Audible that support subscriptionbased and advertising-based podcast business models.

If you remember something called "push" technology from the late 1990s, podcasting may sound familiar. Companies like PointCast Inc. distributed client software that periodically polled network servers, downloading massive amounts of topical content, including audio and video programming, dumping older content from the user's hard drive to make room for the new material. Pointcast's audience could browse the new content without any network latency, which was the rule in those dialup times. It was the first attempt at non-streaming rich media delivery, but "push" was doomed to fail by its business model, which front-loaded costs for everyone — producers paid for distribution, and Pointcast incurred massive bandwidth and technology development expenses that killed the company before it could convert its audience into advertising revenues. The audience got everything for free, although Pointcast had plans to offer subscription-based programs before it collapsed well in advance of the rest of the Internet bubble's bursting.

However, push technology and podcasting are significantly different. Podcasting is built on opensource foundations. Instead of concentrating the distribution channel in the hands of a few companies like Pointcast, podcasting protocols allow any developer to add the ability to query a server to retrieve content to its application or Web service, and most importantly, podcasting allows anyone to place a program into distribution without having to go through an intermediary host that aggregates many channels of information. Pointcast is unneeded in many podcasting scenarios, because the podcaster can communicate directly with the listener. At its founding, podcasting was designed to subvert the economic equations of existing media, thwarting not just the role of the aggregator but also the advertiser.

But much about podcasting remains controversial because of those initial assumptions about the revenue models, or lack thereof.

Discussion of podcasting is difficult, because it is so young. The people who helped launch the industry are very particular about what is a podcast and what isn't. Moreover, they are vocal about it. That is, people talk about podcasts like the form is a kind of poem or book, turning definitions of what a podcast should be into a kind of religious argument. Podcasts, according to programmer Dave Winer, one of the people credited with inventing the technology, should be free — in fact, according to Winer, podcasts were engineered specifically to defy advertisers' efforts to include promotional content in podcasted programs.

"If you're not using MP3, you're probably trying to make podcasting into a replay of previous media," Winer wrote on November 12, 2005, the day after an advertising tracking service was introduced by Audible Inc. "By design, podcasting took a poison pill at the very beginning of its life that made it impossible for the corporate types to subvert it without fundamentally changing what it is. That's why I was sure that Audible wasn't doing podcasting. Basically MP3 can't be rigged up to serve the purpose of advertisers, and that's why I love MP3. And only MP3 provides the portability and compatibility that users depend on. Any other method will force them to jump through hoops that they will resist. If so, then podcasting isn't for the advertisers."

Winer's initial choices about podcasting's technology reflect that he served the poison pill. Yet, by the time he wrote this, podcasts were being delivered in many different file formats, including Quicktime files that played on Video iPods from Apple Computers Inc. The cat was out of the bag, and new uses must and will be found for podcasting or users will route around the rigid boundaries.

In fact, if podcasting is going to remain relevant — and we think it will — the technology will be extremely pliant, supporting many file formats and many more business models. Had the inventors of the personal computer decided what kind of projects it could be used for, the PC would have been designed for failure. In fact, one of the fathers of the PC, Alan Kay, says today that the problem holding back the personal computer today is reliance on the narrow range of ideas he helped think up in the 1970s.