Video and Sound:
Again, these are files that require a "plug-in" or a viewer to see. The latest browsers come equipped to see the most popular files; "Quicktime" and "Real" media files. Most recent computer systems are also equipped to view "Quicktime". File size is more of a consideration with video or sound files because they are relatively large and require time to download them. Be most careful with adding a background sound to your site since it can often hold up the viewable files from being seen until the audio file loads. Video files are extremely compressed in order to keep the file size down. Because of this, image quality ranges from moderate to very poor. They are also small in size, usually not much larger than a postage stamp for dial-up lines. As DSL (Digital Service Lines) become more available, video will improve in quality.

Video and audio files can be "streaming" or "progressive download". "Streaming" means that the viewer can start watching the clip before the entire file is downloaded. The frames that have arrived at the computer are viewed as the remaining frames "stream" in behind them. These files tend to be the most compressed for quick viewing, so quality is minimal. "Progressive download" files must be entirely downloaded to the computers hard drive to be viewed. These can be higher quality but will take longer to download as the file size goes up. They also can be saved by the viewer for later use. "Real" streaming files have the option to not be able to be saved if the presenter wants them available for viewing only.