Understand Formats and Delivery Methods


As you explore multimedia, it’s best to start with the different formats that are available. Just as with graphics, certain formats work best for certain purposes. For example, when deciding on sound files, you might be influenced by the desire for a quick download time as opposed to good sound quality. On the other hand, sound quality might be important to you and you really don’t care how long it takes a file to download. Perhaps both are important to you. All of these factors will influence the choices you make.

Compare Audio Formats

You will encounter several different audio formats as you enter the world of multimedia. Some you will definitely use; others you just need to know about. The formats listed next do not represent all possible choices, only those most commonly used and best supported:

  • m-Law Pronounced moo-law, this format is sort of the granddaddy of them all. If you’re familiar at all with audio files, you might recognize its file extension, .au. This is the file type used on UNIX systems. Although this type of file is supported on most PCs, it doesn’t offer great sound quality.

  • MIDI Musical Instrument Digital Interface is a very different way of producing music and other sounds. Whereas most sound files actually record and reproduce sound and music, MIDI does not. Instead, a MIDI file is somewhat similar to storing the information from a printed page of music in digital format. Although that might be an oversimplification, that’s the basic concept. MIDI doesn’t store music; it stores instructions for creating music. The advantages of MIDI files are that they are very small and download quickly. The disadvantage is that you are limited in the sound you can reproduce because sound is not actually recorded. For example, because MIDI files are built around digitized virtual musical instruments, they cannot be used for voice recordings.

  • Waveform (Wave) Audio If you use a Windows system, you already use Waveform (or Wave) Audio. Are you familiar with the little tune that Windows plays when it loads? That’s a .wav file. These files allow for excellent sound quality but can be extremely large and slow to download.

  • Mp3 Mp3 has been in the news a lot lately. In fact, you might say that Mp3 files have put the music industry in a bit of a quandary. MPEG (Motion Picture Experts Group), better known as Mp3, files are compressed, enabling music to be downloaded easily. The amount of compression is striking. For example, a single song saved as a .wav file can use 40 megabytes of space or more. The same song saved as an .mp3 file might be 1 or 2 megabytes. In light of this, you can understand the Napster controversy. Who would want to take the time to download an album of 12 songs at 40 megabytes each? On the other hand, what if each song is only 1.5 megabytes?

  • AIFF Originally developed for Macintosh systems, Audio Interchange File Format (.aif, .aiff) files provide high quality, although the file size tends to be large. Even though it was a Mac development, .aif files are supported in the Windows environment and can easily be converted to other formats.

  • RM RealMedia files are a special file format designed by RealNetworks for streaming media. Helix Producer Basic, a limited versionprogram that creates these files, is available as freeware.

  • WMA Windows Media Files are Microsoft’s answer to RealNetworks’ streaming media files. The technology is essentially the same, because Microsoft purchased from Real Networks the rights to use their technology.

So, which file type should you use when you are putting together sounds for your Web site? It all depends. If you want to have background music that begins when the page loads, you want a small file that downloads quickly. Your best bet is a MIDI file. If you don’t like the computerized sound that tends to go along with MIDI files, try a very short WAV file. Also, if you want to emphasize sound quality, you’ll lean toward WAV. If your sound clips are long, you will probably want to take advantage of Mp3’s compression capabilities. MPEG files do lose some quality in the compression process, but it is not usually significant. If you want your visitors to be able to listen to the file as it downloads, then streaming media (Real or Windows Media) is your best option.

Compare Video Formats

A slightly less daunting array of choices awaits you when you consider the different video formats that are available. Again, although there are more formats than those discussed here, those listed next are the most common and enjoy the greatest support.

  • Audio/Video Interleaved This format was developed for Microsoft’s Video for Windows. Audio/Video Interleaved (.avi) is the standard for the Windows platform and is used for many applications requiring video. For example, if you have an encyclopedia on CD-ROM, you’ll find that most (if not all) of the video clips contained on it are in the .avi format.

  • QuickTime QuickTime (.mov) is used widely and works well on all platforms. Developed for the Macintosh, it is nevertheless supported in both Internet Explorer and Netscape. QuickTime’s latest versions provide better quality at lower transfer rates because of some new compression routines. Add to that its ease of use and the availability of inexpensive encoding software make the .mov a good choice for newcomers to the world of multimedia.

  • RealMedia Helix Producer 9 can encode video for streaming. Because video files tend to be very large, streaming is a good option if you plan to have video on your pages. Better yet, the basic version is free.

  • Windows Media Likewise, you can use the Windows Media encoding software to create streaming video. As with audio, the software and support that Microsoft provides free of charge makes this an attractive option.

  • MPEG Developed by the Moving Picture Experts Group, MPEG (.mpg) files, like their JPEG counterparts, can be compressed significantly yet lose little quality. In fact, MPEG-4 can provide DVD-quality images. If you are looking for high-quality video reproduction for your site, this is the format of choice. However, MPEG can be complicated, and you will need special software for encoding the videos. This makes MPEG an unlikely choice for a casual user.

    Note

    If you are interested in exploring MPEG in more detail, visit the MPEG4IP Web site at http://mpeg4ip.sourceforge.net and www.apple.com/mpeg4.

Which format should you choose? The main consideration here probably is file size, as video files tend to be very large. For simply attaching a video link or embedding a file, you probably will want to use either QuickTime or AVI. The advantage of using QuickTime is that it is already supported on both Windows and Mac systems. However, if you use AVI clips on your site, Mac users will need to download a plug-in to enable them to view the files. For streaming video, you will probably want to use Windows Media or Real Media.

Understand Delivery Methods

There are two different ways to deliver audio or video to your visitors: download and streaming. Your choice of one or the other will be governed by the size of the file you are planning to use.

If you plan to use only very short clips of a few hundred kilobytes or less, use download as your delivery method. When you link to an audio or a video file, or when you embed multimedia into your pages, the normal method of delivery is by download. In other words, the entire file is downloaded into your visitor’s computer before it is played. With short clips and small file sizes, most people won’t mind waiting. However, if you’re planning to include a long clip—perhaps a lecture, complete songs, or 15 minutes of your Hawaiian vacation video—your visitors likely will move on before the file has time to download. In cases such as this you might want to consider streaming audio and video.

The difference between streaming and downloadable media is very simple: Downloadable audio and video is like filling a glass of water before you take a drink. You wait until the glass is full; then you enjoy the water. On the other hand, using streaming media is like going to a water fountain. You drink the water as it streams up from the fountain’s nozzle. No need to wait for a glass to fill up. With streaming media, the visitor gets to watch the video or listen to the music while the file is downloading.

Shortcut

Even with downloadable files, it is to your advantage to use streaming media. Because streaming audio and video use the UDP protocol (no error checking, hence faster downloads) rather than TCP, the same size file will take less time to download to your visitor’s browser. A longer clip could be used without hindering performance.




How to Do Everything with HTML & XHTML
How to Do Everything with HTML & XHTML
ISBN: 0072231297
EAN: 2147483647
Year: 2003
Pages: 126

Similar book on Amazon

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net