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5.6 Other Multimedia Content
The Web
is completely open-minded about the types of content that can be
exchanged by servers and browsers. In this section, we look at a
different way to reference images, along with audio, video, and other
document formats.
5.6.1 Embedded Versus Referenced Content
Images currently enjoy a special status
among the various media that can be included within an HTML or XHTML
document and displayed inline with other content by all but a few
browsers. Sometimes, however, as we discussed earlier in this
chapter, you may also reference images externally particularly
large ones in which details are important but not immediately
necessary to the document content. Other multimedia elements,
including digital audio and video, can be referenced as separate
documents external to the current one.
You normally use the anchor tag
(<a>) to link external multimedia elements
to the current document. Just like other link elements selected by
the user, the browser downloads the multimedia object and presents it
to the user, possibly with the assistance of an external application
or plug-in. Referenced content is always a two-step process: present
the document that links to the desired multimedia object, then
present the object if the user selects the link. [<a>]
In the case of images, you can choose how to present images to the
user: inline and immediately available via the
<img> tag, or referenced and subsequently
available via the <a> tag. If your images
are small and critical to the current document, you should provide
them inline. If they are large or are only a secondary element of the
current document, make them available as referenced content via the
<a> tag.
If you choose to provide images via the <a>
tag, it is sometimes a courtesy to your readers to indicate the size
of the referenced image in the referencing document and perhaps
provide a thumbnail sketch. Users can then determine whether it is
worth their time and expense to retrieve it.
5.6.2 Referencing Audio, Video, and Images
You
reference any external document, regardless of type or format, via a
conventional anchor (<a>) link:
The <a href=">Kumquat Grower's Anthem</a> is a rousing tribute to
the thousands of 'quat growers around the world.
Just like any referenced document, the server delivers the desired
multimedia object to the browser when the user selects the link. If
the browser finds that the document is not HTML or XHTML but rather
some other format, it automatically invokes an appropriate rendering
tool to display or otherwise convey the contents of the object to the
user.
You can configure your browser with special helper applications that
handle different document formats in different ways. Audio files, for
example, might be passed to an audio-processing tool, while video
files are given to a video-playing tool. If a browser has not been
configured to handle a particular document format, the browser will
inform you and offer to simply save the document to disk. You can
later use an appropriate viewing tool to examine the document.
Browsers identify and specially handle multimedia files from one of
two different hints: either from the file's
Multipurpose Internet Mail Extension
(MIME) type, provided by the server, or from a special suffix in the
file's name. The browser prefers MIME because of its
richer description of the file and its contents, but it will infer
the file's contents (type and format) from the file
suffix: .gif or .jpg, for
GIF and JPEG encoded images, for example, or .au
for a special sound file.
Since not all browsers look for a MIME type or are necessarily
correctly configured with helper applications by their users, you
should always use the correct file suffix in the names of multimedia
objects. See Table 5-1 for more information.
5.6.3 Appropriate Linking Styles
Creating
effective links to external multimedia documents is critical. The
user needs some indication of what the object is and perhaps the kind
of application the linked object needs to execute. Moreover, most
multimedia objects are quite large, so common courtesy tells us to
provide users with some indication of the time and expense involved
in downloading them.
In lieu of, or in addition to, the anchor and surrounding text, a
small thumbnail of a large image, or a familiar icon that indicates
the referenced object's format, is useful.
5.6.4 Embedding Other Document Types
The Web can deliver nearly any type of
electronic document, not just graphics, sound, and video files. To
display them, however, the client browser needs a helper application
installed and referenced. Recent browsers also support plug-in
accessory software and, as described in Chapter 12, may extend the browser
for some special function, including inline display of multimedia
objects.
For example, consider a company whose extensive product documentation
was prepared and stored in some popular layout application such as
Adobe Acrobat, FrameMaker, Quark XPress, or PageMaker. The Web offers
an excellent way for distributing that documentation over a worldwide
network, but converting to HTML or XHTML would be too costly at this
time.
The solution is to prepare a few HTML or XHTML documents that catalog
and link the alternative files and invoke the appropriate display
applet. Or, make sure that the users' browsers have
the plug-in software or are configured to invoke the appropriate
helper application. Adobe's Acrobat Reader is a very
popular plug-in, for example. If the document is in Acrobat
(.pdf ) format, if a link to an Acrobat
document is chosen, the tool is started and accordingly displays the
document, often right in the browser's
window.
