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Screenshot of BBC iplayer: television and radio through the Internet.

Streaming media

by Chris Woodford. Last updated: November 3, 2014.

A decade or two ago, the telephone wire heading into your home was a quaint way to chat with your family and friends when you couldn't speak to them in person. The basic idea hadn't changed much since the 1870s, when Alexander Graham Bell (1847–1922) and others pioneered telephone technology. But in the 21st century, people have started to see telephone lines a different way: now they're broadband Internet connections, piping music downloads, YouTube videos, news, and information—as well as telephone calls—into our homes 24 hours a day. Streaming media (a way of playing files as they download) has been a central part of this information revolution. What is it, exactly, and how does it work? Let's take a closer look!

Photo: BBC iPlayer is a pioneering "on-demand" television and radio player that streams programs down your Internet connection in "real time." That means programs play at the same rate they download, and each program takes roughly the same time to watch via streaming as it would if viewed live on your television.

What is streaming media?

If a picture is a worth a thousand words, a moving picture is worth a million. But how do you cram all that information down a telephone? The trouble is that a couple of copper wires—the basic technology behind our home phone lines—cannot, ordinarily carry information quickly enough to bring things like radio and TV into our homes. If you've ever watched a fax machine chugging along, sending or receiving a printed document at a grindingly slow speed, you'll know just how slow telephone lines can be at carrying anything other than a person's voice (the only job they were ever designed to do).

Real Player screenshot

In the days when most people had dial-up Internet connections (where you make a connection to your Internet Service Provider using a modem to enable what is essentially just a normal telephone call), slow speeds were a major limitation on what could be done online. If you wanted to listen to an MP3 music track (typically about 5 megabytes in size), you could spend half an hour waiting for the entire file to download onto your hard drive, then open it up and play it back. Video files (more likely to be 50 megabytes) would take several hours to download this way, so they were not generally available on the Net. In those days, it was impossible to listen to a music or movie file of any size without a long and tedious wait. The problem was essentially a matter of bandwidth: the speed of an Internet connection (how quickly it can download information) sets a limit to how quickly you can transfer a file.

In the mid-1990s, in the early days of the Web, Rob Glaser and his Real company (originally called Progressive Networks) pioneered streaming media as the solution to this problem. The basic idea is simple. Suppose you want to watch a large video file on your PC. You install a media player (a streaming-media-playing program) on your computer that plays the file while it downloads. So it downloads maybe the first 10 seconds of the file, stores or buffers it, then immediately starts to play it. As the media player starts playing the first part of the file, it's also downloading the next 10 seconds ready for when you come to that bit. The media player never actually stores more than a little bit of the entire file: once it's played part of the file, it deletes it to make way for the next bit. If the media player can download the file as fast as you're watching or listening to it, you'll see no interruptions; if there are delays in downloading for any reason, there will be occasional pauses while the player downloads and "buffers" the next bit of the file.

Photo: Streaming media as it used to be. This is an early version of RealPlayer (the program that kick-started the streaming media revolution) playing here over a 56 Kbps dial-up Internet connection. The status bar at the bottom shows the radio station is being played at 44.1 Kbps (over 44,000 binary digits per second), which is well within the limits of the connection. The trick with streaming media is for the player to adapt to the limits of your Internet connection to avoid excessive buffering.

Downloading and streaming compared

Before we go any further, we need to know more about how the Internet works.

Data (computerized information) moves efficiently across the Internet by being broken up into little bits known as packets. Each packet is independently addressed and travels separately, and different packets can travel by very different routes. Imagine yourself wanting to send a really heavy textbook to a friend in another country. Instead of sending the entire book, you tear it into separate pages, put each one in its own envelope with a separate stamp and address, and mail all those envelopes one after another. Your friend may receive them at slightly different times, in the wrong order, but she can easily reassemble them into the book. Why would you mail a book in such an odd way? It turns out the Internet works best this way with everything broken into small, similar-sized chunks. (We have a whole article about how the Internet works that explains all this in more detail.)

When you download a file in the traditional way, you're effectively asking another computer (a server that sends out files to many different people) to send you zillions of packets one after another and you have to wait for all of them to arrive before you can do anything with any of them. With streaming, you start to use the packets as soon as enough of them have arrived. That's the essential difference. You can think of streaming as playing during downloading, but in fact the two things are different in all sorts of ways:

Examples of streaming media

Genuine streaming

QuickTime screen shot

Most Internet radio stations use genuine streaming, downloading and playing simultaneously with a program like RealPlayer, Apple's QuickTime, or the Microsoft Windows Media Player (the three rival types of streaming). With a broadband connection, you can enjoy audio quality that's not far off the quality you get from a downloaded MP3 file (though, as we discuss in our article on MP3, that's never quite as good as you'd get from a CD). As Internet connections have become faster, and more people have broadband, it's become possible to watch videos and TV programs this way too, though quality is still far short of what you'd get from watching TV or a DVD. That's one reason why online movie stories still often use downloads instead of streaming; if you head for Apple's iTunes store to buy or rent a movie, you'll find you have to download the entire, enormous file (typically 1–2 gigabytes!) before you can watch it.

Photo: Genuine streaming: Apple's QuickTime offers a choice of streaming music and movies. It's only one of three rival streaming technologies.

Pseudo-streaming: progressive downloading

Not all websites that appear to stream video work by streaming. Some (including YouTube) actually use an alternative approach called progressive downloading (fast-start streaming), which is like a cross between conventional downloading and streaming. A large chunk (and sometimes all) of the file you're watching downloads into your web browser's cache (its internal working memory buffer) and your browser plays it simultaneously. Unlike with a truly streamed video, you can't always skip forward: generally you have to wait for the file to download to the point you want to see. Another key difference is that the file remains in your browser cache even when you've finished watching. You can tell when a website is working by progressive downloading because the video window will show two separate indicators on a progress bar, like the one below: one shows you how much of the file has downloaded, while the other shows how much you've played. Typically, progressive downloading uses Macromedia Flash files (with SWF or FLV extensions), that are served from a conventional web server and played on a Flash plugin installed in your browser. It's popular because it's often quicker and easier to implement than genuine streaming.

Example of a progressive download progress bar.
Photo: A progressive downloading progress bar. When you see this, you're not actually streaming a video—you're playing it as you download the entire thing. If you know how to look in your browser cache, you'll probably find the file is sitting in there somewhere after you've played it (look for a very big file or one with a very new date and time, but don't expect to find a meaningful filename or extension).

Where next?

Streaming media—bringing music and videos on demand—may seem advanced compared to the kind of technology people had a few years ago, but it's still relatively primitive. The audio and video information you download has to be compressed dramatically (substantially reduced in quality to make smaller files) so it downloads in a reasonable amount of time. Most streaming videos are still quite small and "pixelated" (full of obvious square blocks) when they play on something like YouTube. That's because even today's best broadband connections are not fast enough to download the huge amount of information in a fullscreen, high-definition TV picture. In a few years time, when broadband connections are many times faster, it will be possible to stream HD-quality video over the Net. Then the age of information-on-demand really will have arrived!

Chart showing how the number of US Internet users watching different kinds of videos has grown between 2007 and 2010.

Photo: Video on the rise: More and more Internet users are now routinely watching videos online—and not just the ones you get on services such as YouTube. Some 69 percent of adult US Internet users (roughly half of all US adults) have watched or downloaded video online (and that figure rises to 84 percent of the people in the 18–29 age group). Men are more likely to watch online videos than women (74 percent compared to 63 percent). Source: Pew Internet & American Life Project, June 2010.

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Text copyright © Chris Woodford 2007, 2011. All rights reserved. Full copyright notice and terms of use.

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Woodford, Chris. (2007/2011) Streaming Media. Retrieved from http://www.explainthatstuff.com/streamingmedia.html. [Accessed (Insert date here)]

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