6.2.1. Pros and cons

There are advantages and disadvantages to streaming audio from a web server. HTTP pseudo-streaming, for example, is a good option for serving RealAudio and RealVideo files on the Web without the added management requirements and expense of server-side streaming software. And from the developer's point of view, there's no added work because RealAudio and RealVideo files require no special handling for HTTP serving.

Finally, HTTP does not perform well under heavy server loads. But for sites serving no more than a handful of simultaneous streams at any given time, this is a great way to add streaming audio and video features to your web site without incurring extra costs.

6.2.2. Requirements for HTTP streaming

audio/x-pn-realaudio

Files with a .ra, .ram, or .rm file extension

audio/x-pn-realaudio-plugin

Files with a .rpm file extension

Many servers already use the appropriate MIME types. If not, it's a relatively simple process to configure your host server for these types, and you can request that your service provider add this feature for you.

Let's take a quick look at how to broadcast RealAudio clips from a web server. Most popular web servers automatically support the .ra and .ram extensions. However, you may need to add the more recent .rm and .rpm file extensions since many web servers do not yet understand them. Note that many of the problems associated with embedding the player in web pages spawn from missing or incorrect MIME typing.

6.2.3. HTTP streaming tutorial

All things audio   Exactly on the hour, a lone SGI Challenge computer in the middle of Washington, D.C., opens its audio input port, receives a five-minute live news update, converts the audio signal to the appropriate format, sends the file to the RealServer, and then streams it across the globe without the touch of a human hand.   For National Public Radio's webmaster, Robert Holt, processing and encoding NPR's daily programming is one of the greatest challenges of broadcasting RealAudio content. Robert created a custom Unix script to automate the entire RealAudio conversion and streaming process for NPR's hourly news update.   At 55 minutes after the hour, NPR's SGI Indy machine runs a time query that syncs the machine's internal clock with NPR's master clock. Then, at exactly one minute past the hour, the SGI opens its built-in audio port and records a five-minute live feed from NPR's broadcast sound studio. At seven past the hour, the SGI computer converts the five-minute AIFF file to a WAV file. A script then commands the RealEncoder to encode the file and place a time and date stamp into the .ra file. Finally, the script copies the file through a firewall to NPR's RealServer, replacing the previous five-minute news update file.   NPR's system configuration is a dedicated audio server consisting of a RealServer 5.0 running on a Sun Sparc 20 and Netscape Enterpriseweb server software running on an SGI Origin 200 server. The system includes 128 MB of RAM to ensure enough memory for NPR's thousand-stream license, and a 10 GB hard drive to hold NPR's RealAudio content. NPR has a partial T3 connection (equivalent of five T1 lines) to the Internet.   Installing the system was a simple process for Robert: "For the most part, installing the RealServer is a just a matter of configuring your MIME types and going through the automatic installation process." And there was little trouble keeping the system running smoothly. In fact, the hardest part about maintaining the RealAudio System is not the server but the content. "It's easy to get the system up and working. The hard part is feeding the beast new content and retooling your audio files with the newest codecs."   Robert works as part of a three-person team, editing, encoding, and administering the delivery of over five hours of daily programming, in addition to the five-minute hourly news update. Since the installation of NPR's RealServer in 1995, Robert has edited, processed, and served many RealAudio files. Here are some of his tips for getting quality results from RealAudio:   Use the highest-quality source audio files you can get. Internet compression algorithms, especially higher-bandwidth 40 and 80 Kbps codecs magnify mistakes or glitches in the original recording. NPR is fortunate enough to use source files that have been recorded in their custom $150,000 broadcast studio, with top-of-the-line Neumann condenser microphones. All the audio is recorded from the very beginning with the proper equalization and compression. Note that even if you do not have a deluxe studio, there are steps you can take to capture high-quality source material. See Chapter 3, "Capturing Original Source Material" and Chapter 4, "Optimizing Your Sound Files" for more information.   Make sure you have plenty of disk space for all of your content. An hour of content encoded with the RealAudio 28.8 algorithm fills 8 MB. All your programming, especially if you keep archives on disk, can quickly add up to a huge amount of disk space.   Make sure your connection to the Internet is stable and that you are using a high-quality Internet Service Provider. Call your ISP and check the data throughput with a program such as Net Medic.   Make sure your ISP has enough bandwidth to deliver all your streams. One of the most common problems with the RealAudio System is not the system performance or the CPU speed, but inadequate bandwidth. Typically, bandwidth on the Internet router gets swallowed up first. There is not much you can do about that, but you can make sure your connection to the Internet is big enough to meet your needs.   If you are broadcasting from your own in-house server, always watch system performance. Keep an eye on CPU usage and keep the load balanced between two servers. Always pay attention to memory and system speed.