Web Audio Today

Webcasts, Streaming, and Compression

Webcasts are broadcasts on the Web. Webcasts can be live events or recorded material and like traditional broadcast media, webcasts can be viewed by many people at the same time. When a Web site serves recorded material, each visitor can begin playback at any time. One visitor may be half way through a video webcast while another is just beginning the playback. As a result, webcasts offer enormous flexibility for the delivery of presentations on the Web.

Webcasts are made possible by a technology known as streaming media. Before streaming came on the scene in 1995, media files had to be completely downloaded before any playback could begin. Those with slow connections to the Internet had to wait minutes or even hours for audio or video data to download. Streaming changed all that. Digital content is first compressed and then broken into small packets of data. These packets are sent sequentially over the Internet to the Web site visitor. The visitor's computer places these packets into a buffer. When the buffer has enough packets then playback begins. During playback, the visitor's computer continues to download, buffer, and que up more packets to create continuous playback. Of course, when the network gets congested, the playback of one set of packets sometimes ends before the next set of packets is ready. At that point, the broadcast ceases to be continuous and the visitor usually misses some content.

It is technically possible to stream media using the old Hypertext Transport Protocol (HTTP) but the nature of that protocol is not conducive to the continuity needed for music and video. The User Datagram Protocol (UDP) and the more recent Real Time Streaming Protocol (RTSP) were both developed to make streaming more reliable. Both of these protocols keep sending data even if previous packets never reached their destination. That puts a priority on continuity so visitors may experience only an occasional hiccup in the audio or video stream instead of major gaps. Today RTSP is the preferred protocol in use by all major streaming technologies.

After the visitor is finished viewing the streaming media, you might think that the complete media file is stored somewhere on the visitor's hard drive and would be available for off-line playback at some other time. That is not the case with streaming. If the visitor wishes to view the media again, an Internet connection is required and the streaming process must begin anew. Streaming, therefore, affords the content provider a bit more control over their intellectual property. Savvy computer users, of course, can use any of a number of software programs to capture the stream to their hard drives for later off-line playback.

Streaming alone, however, would not be adequate for sending lengthy broadcasts over the Internet. Compression of the data is also needed. Uncompressed audio and video files are far too large for practical transmission on the Internet. A single minute of stereo audio at CD quality, for example, takes up about 10 megabytes of data. When compressed, however, the same audio often takes up only 1 megabyte or less. The best compression technologies today, such as MP3 for audio and MPEG-4 for video, create very small audio files that sound almost as good as the original uncompressed audio. Compression technologies for audio and video reduce file size by removing data from the file according to a set of rules called a codec (COmpression DECompression). When the visitor receives the smaller file, the media player application (RealOne, QuickTime, or Windows Media Player) attempts to reconstruct the original file using the same set of rules.

One way to understand compression-decompression is to imagine you need to send someone a series of important dates from the 20th century such as the following dates when major wars began. A very simple codec might remove the first two numbers of each set of four. The dates could then be transmitted in a file half the size of the original.

When the visitor receives this file, our simple codec inserts 19 before each set of two numbers to reconstruct the original file. This simple example would result in a lossless compression because the final reconstructed file would be identical to the original. Unfortunately, Audio and video compression is more complex and the final reconstructed file is not identical to the original. This is known as lossy compression. Today's compression technologies, however, are so refined that the loss of quality is often minimal and the quality is more than acceptable for most people.

How Does Streaming Work?

Streaming media requires an audio and/or video source, a computer for encoding and compressing the data, and a dedicated server to send the encoded data at whatever rate is needed by the end user. A dedicated streaming media server is required to ensure that the computer serving the files is not burdened with requests for other types of files such as Web pages or graphics.

From the visitor's point of view here is what happens.

1. The visitor clicks a link to view or listen to streaming media. The URL for the link probably begins with rtsp:// because the file is served with Real Time Streaming Protocol (RTSP) instead of HTTP.
2. The Web browser contacts the streaming media server at the address found in the link. The browser asks the streaming media server to begin sending the media.
3. The streaming media server begins to send data packets to the visitor's computer.
4. The visitor's computer responds by launching a plugin or application and begins storing the data packets in a buffer.
5. After a few seconds of buffering the playback begins.
6. During playback, additional packets are received, stored in the buffer, and placed in the que for playback.
7. If network conditions are good, the playback will be continuous.

When To Use Streaming

If your Web site uses short sound samples of 20 seconds or less, setting up a dedicated streaming media server is probably not a great use of your time. Connection speeds today are adequate to allow visitors to download short audio samples so streaming isn't really needed. Streaming is most appropriate when you wish to make large media files available for viewing by tens or hundreds of people at the same time.

Who is Streaming?

If you have the bandwidth today, you can enjoy news, sports, music, film, radio, and other entertainments using a Web browser in combination with Web browser plugins and stand-alone applications. Webcasts can be either live or pre-recorded digital audio and/or video that is streamed to the visitor. Almost all the major media companies offer Webcasts today and it is becoming easier for smaller Web sites to offer streaming media files. The streamed file can be either embedded in a Web browser window using a plug-in or ActiveX control or played by a stand-alone application. Increasingly television networks are making their shows available as streaming media. Those with fast Internet connections today have many more choices in video entertainment than they did a few years ago.

What are the Formats?

Some of the major streaming technologies today include RealOne, Windows Media Player, QuickTime, and Flash. RealNetworks, the maker of RealOne, has done a great job of making an easy-to-use player (RealONE player) that works reliably on Windows, Macintosh, Linux, and various UNIX platforms. They also make streaming server technology and offer business services to help content providers track and manage large numbers of users. RealNetworks has products for every stage of streaming media development from content creation to delivery.

RealNetworks markets a streaming server called the Helix Universal Server (previously RealServer 8). The Helix Universal Server is very popular because it provides services vital to streaming media customers. First, it delivers content specially encoded for different bandwidths. If a visitor is using a dial-up modem, the server automatically chooses media encoded for slower connections. The quality of the experience, therefore, varies with the bandwidth of the visitor. Second, the Helix Universal Server supports the RealVideo codec as well as codecs from QuickTime, Windows Media Player, and about 50 other formats. RealNetworks technologies also support digital rights management technologies to protect intellectual property rights of content creators. For the latest details, see their page at: http://www.realnetworks.com/products/media_delivery.html.

Microsoft has its own complete package for creating and delivering streaming media. Microsoft's solution consists of a set of authoring applications (Microsoft Producer and Windows Media Encoder), a streaming server solution that works only with Microsoft Web servers, and a player application (Windows Media Player) that works on Windows. Microsoft does not support Macintosh or any UNIX or Linux platforms. Its lack of broad and consistent platform and browser support detracts from what is otherwise a good product. For the latest details, see their page at: http://www.microsoft.com/windows/windowsmedia/forpros/serve/features.aspx

Apple makes the QuickTime Streaming Server and QuickTime Player application. They also make QuickTime Broadcaster for encoding live webcasts. QuickTime supports more than 100 media types including MP3, Flash, all major graphic file formats, DV, MIDI, and many more. Apple's QuickTime Streaming Server works on MacOS X server but Apple has also created an open source version called Darwing Streaming Server that can be used on Linux and most UNIX systems. QuickTime is often the choice among video professionals and QuickTime also offers much to audio professionals as well. For the latest details, see their page at: http://www.apple.com/quicktime/streamingserver/

Flash FLV format has been around since the early 21st century but the popularity of YouTube may be the reason that FLV has become so popular today. FLV formatted videos play on any web browser configured with the Flash player software. That constitutes the vast majority of web browsers today so the FLV format is the best choice if you wish to reach as many customers as possible. For the latest information about the Flash Media Server, see http://www.adobe.com/devnet/flashmediaserver/.

One Man's Opinion

My experience with the various Webcast technologies is that they are all great for convention keynote addresses, investor relations speeches, and slide shows with background audio and narration. When the focus is on music, however, I have found that QuickTime delivers the best quality audio and video. That's probably why movie trailers are almost exclusively made available on the Web in QuickTime format.