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Feed Enclosure Generation
In the videoblogging world it is still too difficult to set up a
syndication feed with enclosures. This document will attept to enumerate
some best practices that work with current tools.
Let's walk through the steps of the typical videoblogging/podcasting
process. There are other ways of doing of course, but I'll pick a fairly
typical one.
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Create a video or audio file.
Using desktop computer software or a mobile device, a user
creates an audio or video file that they wish to publish on their
blog.
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Put the file on a web server.
Using some kind of hosting service, the user uploads the
multimedia file to a web server.
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Create and publish a blog entry
Using either a web browser or a specialized program, the user
creates a blog entry with a link to the multimedia file and publishes
it to their blog.
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Create a syndication feed with enclosures
This step should be automatic, but frequently requires manual
editing of XML files or signing up for a service that will take a
standard blog feed and automatically create the proper enclosure
format.
In some processes these steps are combined to make things easier for
users, and the main focus of this document is how to combine Step 3 and Step 4, and
when the blog software doesn't (yet) provide an automated mechanism for
doing this, to provide a method for podcast clients or videoblog
aggregators, like ANT, to find the intended enclosures from a feed that
doesn't support the RSS 2.0 enclosure tag or the Atom 0.6 link tag.
Marking Enclosures in the Content of a Blog Entry
The best practice (it seems) for marking an enclosure in the
(X)HTML content of a blog entry, is by using the rel attribute of a
link, as demonstrated in this example: <a
href="http://pb.vlogcentral.com/movies/11899.mov"
rel="enclosure">Click to play</a>Since RSS 2.0
only allows one enclosure per blog entry, there should only be one link
in the blog (X)HTML that is marked with the rel="enclosure"
attribute.
Describing
Enclosures in HTML by Andreas Haugstrup describes this method in
more detail. (Although he prefers people to link to a docment of broader
scope called HTML
Meta Profile for Blogs which contains additional
recommendations.)
Automatically Creating an RSS 2.0 Enclosure Element from a Blog
Entry
There are several tools that automatically create RSS 2.0
enclosure elements from blog entries, and many of them use the
rel="enclosure" attribute to decide which link should
be the enclosure. Some tools will only use links marked with
rel="enclosure" others will use various heuristics to
identify multimedia enclosure files. The (proposed) best practice is to
always use the rel="enclosure" attribute to mark
enclosures in the blog content. A partial list of tools that support
this mechanism follows:
| Movable
Type |
Josh Kinberg created the MT-RelEnclosure
Movable
Type plug-in that creates RSS 2.0 enclosures from the
rel="enclosure" attributes by extending an
existing enclosure plug-in.
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| WordPress |
See this post.
(more later.)
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| FeedBurner |
FeedBurner is a web-based
service for enhancing (Atom and RSS) syndication feeds.
The SmartCast feature of FeedBurner will use the
rel="enclosure" marker if it is present,
otherwise it will fall back to other methods of locating the
enclosure. This page
explains how it works.
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![[Note]](graphics/note.gif) | Note |
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If you know of a web service, blog service, blog package or
plug-in that created RSS 2.0 enclosures from the
rel="enclosure" attribute, please post a message on
the audvidsyn
Yahoo group, and I'll add it to this list.
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| Note |
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There are other mechanisms for creating RSS 2.0 enclosures from
blog entries, but this "best practices" document will only list and
support methods that use the rel="enclosure" indicator.
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Automatically Creating an Atom Enclosure Link Element from a Blog
Entry
Enclosures are handled in Atom with a link
element with the rel="enclosure"
attribute. At this point I don't know of any tools that will
generate an Atom enclosure link element from an HTML
a element with the rel="enclosure"
attribute.
Finding Enclosures Without an "enclosure" Element
Unfortunately, at present, very few blog servers will create an RSS
2.0 enclosure tag or Atom link tag
for your audio or video enclosure in a blog entry. Although
feed-enhancement services, like FeedBurner, can be valuable in many ways,
they do require a new videoblogger or podcaster to sign up for and
configure one more service. Installing a Movable Type or other plug-in is
also a serious barrier for beginners. For hosted blog services, such as
Blogger or Typepad, the user does not even have the option of installing a
plug-in.
This section presents a mechanism for multimedia aggregators, such
as ANT, to use the rel="enclosure" mechanism to find
enclosures on blogs that do not have the capability of creating enclosure
elements. Note that this mechanism should only be used as a fallback when
there is no enclosure element in the RSS feed. Here is the proposed
algorithm:
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Look for an enclosure in the syndication metadata for the
current blog entry.
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If an RSS 2.0 feed, look for an enclosure
element within the item element for the blog
entry.
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If an Atom feed, look for a link element
with the rel="enclosure" attribute within the
entry element for the blog entry.
This is what most podcast and videoblog clients do today (with
RSS 2.0 feeds)..
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Look for an a element with the
rel="enclosure" attribute inside the RSS
description or atom content
element
In this case the multimedia aggregator is using the same method
as a feed-enhancement service, blog package, or blog plug-in would
(some would say should) have used to create an enclosure element. If
the link to the enclosure made it into the description/content of the
item/entry, then it is not necessary for the multimedia aggregator to
make the additional HTTP request required by the following
step.
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Follow the link element in the feed to the
complete HTML item and look for an a element with
rel=enclosure
This step will require an extra HTTP access, but will allow an
aggregator to search the entire blog post for a link to an enclosure.
Since a podcast or videoblog client will be downloading large
enclosures the overhead of reading an extra HTML page (without loading
images) should not have a significant impact on performance.
![[Caution]](graphics/caution.gif) | Caution |
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This could be tricky on blogs that don't have a permalink to
an individual HTML page for each permalink entry, but instead link
to an anchored HTML fragment within a multiple-entry archive page.
Does anyone have any thoughts on this? If so, post it to the audvidsyn
list.
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This document suggest "best practices" for service providers and
tool makers who wish to create the best possible user experience in the
current Internet ecosystem. As the blog packages and blog service add
built-in support for using the rel="enclosure" marker,
the method proposed in the section called “Finding Enclosures Without an "enclosure" Element” can be
phased out. In the meantime, we can make it easier for more people to
podcast and videoblog and promote the adoption of the
rel="enclosure" standard.
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