Streaming audio: Good.
Streaming video: Bad.
Most users still do not have sufficient bandwidth to receive streaming video in an acceptable quality - and they won't get broadband for another four years . Jerky, low-res video that breaks up several times per minute simply does not constitute "compelling content."
It is rare that current-quality streaming video could not be replaced by a few still images and a transcript . In fact, most sites would improve if they replaced streaming video with an alternative format such as a comic strip-like sequence of photos with captions. Not only can the photos employ much higher image quality, but the user will also be able to scan the presentation and easily focus on those segments that interest him or her.
In contrast, streaming audio has sufficient quality to be used whenever audio is an appropriate way of communicating with the user.
Video: Download Usually Better Than Streaming
Because of the poor quality of streaming video, it is often best to digitize a higher-quality version of the video and make it available for download. If the video actually has value, then users won't mind waiting, say, five minutes to download a one-minute video where they can actually see something.
For any download that will take more than 10 seconds at the bandwidth available to most of your users, you should state the size of the file. For most sites, this means that they should indicate the size of anything larger than 50 kilobytes . Also state the file format if you are using any type of non-standard format.
Before users decide to invest in a long video download, it is necessary for them to understand what they will be getting. They won't click on something just because it's available: there is too much stuff on the Web these days.
Provide previews of all multimedia objects on plain HTML pages ( see example ). In the case of videos, it is often a good idea to include one or two still photos. Also, for both audio and video, write a short summary of what the user will get to hear/see. The title alone is usually insufficient. Also state the running time of the clip.
Keep It Short; Segment Into Chapters
Linear playbacks are very passifying and conflict with the basic Web user experience which is one of taking control and moving around. Most audio and video clip should be less than one minute . Sitting still to watch something that takes more than five minutes should be the rare exception on the Web.
For example, instead of putting an entire 30-minute keynote lecture on the Web as streaming audio or video, put up text files with a transcript. If possible, employ an editor to edit the transcript into something that is more readable than most lectures. Then supplement the text with a few photos of the speaker and the audience as well as high-quality versions of any visuals. Finally, you can communicate the speaker's personality and the spirit of the event by linking to a one-minute audio clip of the most exciting sound bytes. Or use a video clip if the speaker was sufficiently animated.
To preserve the feeling of user control, even when presenting multimedia, segment longer presentations into short chapters that can be chosen from a menu. For example, when converting a television news program to the Web, don't make it into a single, 60-minute streaming video that cannot be controlled by the user. Instead, break the program into one segment for each news story. Then prepare a standard Web page that lists the stories with a short summary and a single thumbnail photo from the most visual ones. Allow users to link to individual stories from this page.
Stay a Version Behind
No matter what multimedia technologies you use, it is always best to stay at least one year behind the evolution in the play-back software. Restrain yourself to using encoding formats that will work with old software since many of your users will not have upgraded yet.
If users have to download a new plug-in or install new software to view your site, then most of them will simply go away. It currently takes at least a year before new software releases are sufficiently widely used that it is safe to depend on them.
Instead of simply demanding that users install special software to access your site, it is better to show a preview of the multimedia content that can be accessed without anything except a standard (two-versions old) browser. After the users have seen this preview, they may be motivated to spend the time and effort (and risk of crashing) to get the necessary software. If they don't have a good idea of what they will get, then why should they care?
Any time you use any format other than plain text and standard HTML, you risk depriving users with disabilities from being able to use your site. This is one more reason to restrain use of multimedia to cases where it adds substantial value to a site.
Deaf users can be supported by the use of captions on videos and transcripts of audio presentations. Such textual alternatives also make the content more accessible to search engines and facilitate translation.
Blind users are harder to support. The traditional approach to making images accessible is to provide a textual description that can be read aloud by a talking browser, but doing so for a video can conflict with the audio track. WGBH, a PBS station in Boston, recommends the use of DVS (Descriptive Video Service) with a separate audio narrative that runs between the pauses in the main audio track for users who can't see the pictures. For some videos, this may work. Other times, it may be necessary to provide a completely textual alternative that integrates the information found in the audio and visual tracks of the video.
Many visually impaired users are not completely blind but do have reduced vision. Often, such users can be supported simply by a bigger or cleaner video image (even if it takes longer time to download) or by providing a slide show presentation with cleaned-up (and possibly simplified) still images as an alternative to a moving-image presentation.
(See additional guidelines for usability of websites for users with disabilities.)
1995 Multimedia Guidelines Revisited
For additional advice, see my Alertbox from 1995: Guidelines for multimedia on the Web.
Even though this article was written almost a lifetime ago in "Internet years," I still stand by my comments and recommendations. The main changes since 1995 are the emergence of new implementation tools and the rapid obsolescence of the technologies that were prominent in 1995. Most of the examples I linked to in 1995 are either gone from the Web or they only work in old browsers that run old versions of Java. But the design principles and guidelines are the same.
The most depressing aspect of revisiting my article from 1995 is that I recommended seven uses of animation but that the first six are almost never found, even today. The seventh use, attracting attention, is usually employed the wrong way.
One change since 1995 is that this continued erroneous use of animation is starting to backfire : there is too much animation that has no usability benefits to the user but is simply used to try to attract attention to something that is irrelevant (usually advertising banners). Users have realized this and are now avoiding design elements that move in the belief that they are probably useless.
I was too optimistic back in 1999 in assuming that broadband access would be widely available "in four years" (i.e., 2003). As of early 2004, most people are still using dial-up:
United States, 38% of home users have broadband
Europe: 26% of home users have broadband
Despite the slow uptake of broadband, there are now enough users on broadband that it is possible to include streaming video on websites as long as the video clips remain secondary to simpler media forms that will work for all users. It's also possible to deliver targeted for-pay services -- such as video of sporting events -- to a more narrow audience that has self-selected based on its technical capabilities.
Basically, the guidelines from 1999 continue to hold, in particular the advice to:
keep videos short; long video is boring in an interactive medium
segment long presentations; allow direct access to individual elements
provide previews on standard pages; include descriptions of what users will get
remember accessibility, especially for government projects
These guidelines are likely to be the basis for successful use of multimedia on the Web, even when my prediction of wide-spread broadband comes true. (I am not going to guess when, but it's going to be several more years.)
Update 2005: Guidelines for Good Web Video Starting
Video is now getting to be more acceptable technically speaking. Our eyetracking studies of Web video has started generating some new guidelines for the usability of such content.