a Tuesday feature
Creating Audio Files for the Web
Many of you have asked about creating streamable files using Shockwave Audio. So, here's how to do it.
Remember bandwidth will still be our main concern with this entire process. The main thing we want to keep in mind is the bit rate, this will be the greatest factor in controlling the stream rate for different connection speeds. When choosing a bit rate, keep the system resources of your users in mind. If you estimate that your users will have slower modem connections, choose a low bit rate. If you know your users will connect using fast T1 lines, you can afford to choose a higher bit rate and go for better quality. Low bit rates are generally appropriate for the Internet, while higher bit rates are more appropriate for Intranet distribution.
The following list offers some example bit rates to use for a particular speed of connection. Remember that the Internet is not guaranteed to deliver the bandwith you might think it will. Be sure to overestimate a little so that you can provide the best streaming possible for your clients and the people who will visit thier sites.
- 64 kbps to 128 kbps--T1 delivery
- 32 kbps to 56 kbps--ISDN lines
- 16 kbps--28.8 modem connection
- 8 kbps--14.4 modem connection
Steps for Creating Streamable Audio Files (SWA Files)
Use the SWA Export Xtra to export a standard audio file from SoundEdit 16 as a shocked audio file designed specifically for the Web. When you create an audio file with the SWA Export Xtra, the new file is compressed to reduce download time. The file format of the new file is .SWA.To use the SWA Export Xtra:
1.In SoundEdit 16 version 2, open the audio file you want to export.
2.Choose Shockwave for Audio Settings from the Xtras menu to configure the compression options.
3.Select the bit rate (kbps) you want from the Bit Rate drop-down menu.
The bit rate determines both streaming rate and quality of output. A low bit rate produces a file that can stream at lower baud rates, but may lose some quality. A higher bit rate produces files that require higher baud rates for streaming, but are of higher quality. For example, 144 kbps per second produces very high-quality audio, but also results in files that require a longer time to download.
4.Check the Convert Stereo to Mono checkbox if you want to convert a stereo file to mono. The SWA Export Xtra automatically converts a file to mono if you choose a bit rate of 32 kbps per second or less.
5.Choose OK to close the Shockwave for Audio Settings dialog box.
6.Choose Export from the File menu to open the Export dialog box.
7.Choose .SWA File from the Export Type drop-down menu.
8.Name the file, then choose Save. The file is exported using the settings you specified in the Shockwave for Audio Settings dialog box. When you name the file, you must follow the file naming conventions of the server from which the file will be played. Depending on the limits imposed by the file system of your server, you can use file names of up to 27 characters plus the .SWA file extension. Use a name of eight or fewer characters plus the .SWA file extension if this limit is imposed by your server. If the SWA file is streamed over the Internet, the file name is case-sensitive and neither spaces between words nor special characters are allowed.
Some Guidelines for Creating Audio Files from Macromedia
When preparing an audio file for export as a SWA file, the following guidelines are recommended by Macromedia:Work with 22.050 or 44.100kHz files (22.050kHz recommended).
When using preexisting 8-bit or 11kHz files, up-sample them to 16-bit 22.050kHz and leave them at this resolution when exporting to SWA format. You might find that performing some EQ operations within SoundEdit 16 will better the quality of SWA files encoded at modem speeds (8 kbps and 16 kbps). For example, some filtering of frequencies in the range of 4kHz to 8kHz (in the context of a 22.050 sample rate) can reduce crunch and distortion on certain files.
Close SoundEdit 16's Levels palette when exporting SWA files.
Be aware that 11k stereo source files are automatically converted to mono in all cases.
It is recommended that stereo source files share common information between the two channels. If the two channels carry unrelated information, the result will be a very uneven quality level between the channels.
Once you've created the .SWA file, you can place it on a Web page using any of the template movies included with Shockwave, or you can use the SWA Streaming Xtra to include it in a custom Director movie.
Until next week, feel free to send any questions you might have. Soon we'll move on to some detailed step-by-step examples and tutorials.
