How Streaming Video and Audio Work

If you have a connection to the Internet and you want to find streaming video and audio files, you shouldn't have to look far. Sound and video have become a common part of sites all over the Web, and the process of using these files is pretty intuitive. You find something you want to watch or hear -- you click it, and it plays. Unless you're watching a live feed or a webcast, you can often pause, back up and move forward through the file, just like you could if you were watching a DVD or listening to a CD.

But if you've never used streaming media, your computer may need a little help to decode and play the file. You'll need a plugin for your Web browser or a stand-alone player. Most of the time, the Web page you've visited points you in the right direction. It prompts you to download a specific player or shows you a list of choices.

These players decode and display data, and they usually retrieve information a little faster than they play it. This extra information stays in a buffer in case the stream falls behind. There are four primary players, and each one supports specific streaming file formats:

• QuickTime, from Apple, plays files that end in .mov.
• RealNetworks RealMedia plays .rm files.
• Microsoft Windows Media can play a few streaming file types: Windows Media Audio (.wma), Windows Media Video (.wmv) and Advanced Streaming Format (.asf).
• The Adobe Flash player plays .flv files. It can also play .swf animation files.

For the most part, these players can't decode one another's file formats. For this reason, some sites use lots of different file types. These sites will ask you to choose your preferred player or pick one for you automatically.

The QuickTime, RealMedia and Windows Media players can work as stand-alone players with their own menu bars and controls. They can also work as browser plugins, which are like miniature versions of the full-scale player. In plugin mode, these players can look like an integrated part of a Web page or pop-up window.

Flash video is a little different. It usually requires a Flash applet, which is a program designed to decode and play streaming Flash files. Programmers can write their own Flash applets and customize them to fit the needs of a specific Web page. Flash is becoming a more popular option for playing streaming video. It's what YouTube, Google Video and the New York Times all use to display videos on their sites. The video below, which demonstrates what would happen if you shot your TV, plays in a Flash applet.

Regardless of whether it's an applet or a fully functional player, the program playing the streaming file discards the data as you watch. A full copy of the file never exists on your computer, so you can't save it for later. This is different from progressive downloads, which download part of a file to your computer, then allow you to view the rest as the download finishes. Because it looks so much like streaming media, progressive downloading is also known as pseudo-streaming.

These players and applets do what many applications do -- they play files. We'll look at these files and how they travel to your computer in the next section.