Enclosure Tags

In the beginning (RSS 0.92), RSS carried attached files (such as MP3 files) to RSS readers through a mechanism called enclosure tags. While most podcast listeners will use one of the podcast clients such as iPodder or iTunes to subscribe to your podcast, you should be prepared for those who are still using an RSS news reader. For them, let's talk about enclosure tags.

An enclosure tag is one of the optional elements that exists in RSS 2.0. Like so many elements, it provides a way to describe pieces of information beyond the basics of a story link and channel description. <enclosure> is an optional subelement of <item>. Looking back at Listing 9.1, the enclosure tag should be inserted just before the </item> tag for each episode of the podcast.

The enclosure tag has three required attributes. "url" is the location of the enclosure, "length" is the file length (in bytes), and "type" is the type of file it is, expressed as one of the standard MIME types.

<enclosure url="http://www.ABG2Podcasting.com/mp3s/EarlyPodcast.mp3" length="18218340" type="audio/mpeg" /> 

The list of standard MIME types shown in Table 9.1 shows that enclosure tags can be used for more than just podcasts, but for most podcasters it will be enough to know that they can be used to allow a listener who's committed to an RSS news reader to subscribe to, and receive, the podcast. You should understand that not every RSS news reader can handle enclosures such as podcasts, but while the computer industry is still trying to figure out how to build support for RSS (and all its related media types) into operating systems and applications, a version of your RSS feed with enclosure tags may expand the potential audience for your podcast.

Table 9.1. Mime File Types Cover Far More Than Just Audio

ai	application/postscript
aif	audio/x-aiff
aifc	audio/x-aiff
aiff	audio/x-aiff
asc	text/plain
au	audio/basic
avi	video/x-msvideo
bcpio	application/x-bcpio
bin	application/octet-stream
c	text/plain
cc	text/plain
ccad	application/clariscad
cdf	application/x-netcdf
class	application/octet-stream
cpio	application/x-cpio
cpt	application/mac-compactpro
csh	application/x-csh
css	text/css
dcr	application/x-director
dir	application/x-director
dms	application/octet-stream
doc	application/msword
drw	application/drafting
dvi	application/x-dvi
dwg	application/acad
dxf	application/dxf
dxr	application/x-director
eps	application/postscript
etx	text/x-setext
exe	application/octet-stream
ez	application/andrew-inset
f	text/plain
f90	text/plain
fli	video/x-fli
gif	image/gif
gtar	application/x-gtar
gz	application/x-gzip
h	text/plain
hdf	application/x-hdf
hh	text/plain
hqx	application/mac-binhex40
htm	text/html
html	text/html
ice	x-conference/x-cooltalk
ief	image/ief
iges	model/iges
igs	model/iges
ips	application/x-ipscript
ipx	application/x-ipix
jpe	image/jpeg
jpeg	image/jpeg
jpg	image/jpeg
js	application/x-javascript
kar	audio/midi
latex	application/x-latex
lha	application/octet-stream
lsp	application/x-lisp
lzh	application/octet-stream
m	text/plain
man	application/x-troff-man
me	application/x-troff-me
mesh	model/mesh
mid	audio/midi
midi	audio/midi
mif	application/vnd.mif
mime	www/mime
mov	video/quicktime
movie	video/x-sgi-movie
mp2	audio/mpeg
mp3	audio/mpeg
mpe	video/mpeg
mpeg	video/mpeg
mpg	video/mpeg
mpga	audio/mpeg
ms	application/x-troff-ms
msh	model/mesh
nc	application/x-netcdf
oda	application/oda
pbm	image/x-portable-bitmap
pdb	chemical/x-pdb
pdf	application/pdf
pgm	image/x-portable-graymap
pgn	application/x-chess-pgn
png	image/png
pnm	image/x-portable-anymap
pot	application/mspowerpoint
ppm	image/x-portable-pixmap
pps	application/mspowerpoint
ppt	application/mspowerpoint
ppz	application/mspowerpoint
pre	application/x-freelance
prt	application/pro_eng
ps	application/postscript
qt	video/quicktime
ra	audio/x-realaudio
ram	audio/x-pn-realaudio
ras	image/cmu-raster
rgb	image/x-rgb
rm	audio/x-pn-realaudio
roff	application/x-troff
rpm	audio/x-pn-realaudio-plugin
rtf	text/rtf
rtx	text/richtext
scm	application/x-lotusscreencam
set	application/set
sgm	text/sgml
sgml	text/sgml
sh	application/x-sh
shar	application/x-shar
silo	model/mesh
sit	application/x-stuffit
skd	application/x-koan
skm	application/x-koan
skp	application/x-koan
skt	application/x-koan
smi	application/smil
smil	application/smil
snd	audio/basic
sol	application/solids
spl	application/x-futuresplash
src	application/x-wais-source
step	application/STEP
stl	application/SLA
stp	application/STEP
sv4cpio	application/x-sv4cpio
sv4crc	application/x-sv4crc
swf	application/x-shockwave-flash
t	application/x-troff
tar	application/x-tar
tcl	application/x-tcl
tex	application/x-tex
texi	application/x-texinfo
texinfo	application/x-texinfo
tif	image/tiff
tiff	image/tiff
tr	application/x-troff
tsi	audio/TSP-audio
tsp	application/dsptype
tsv	text/tab-separated-values
txt	text/plain
unv	application/i-deas
ustar	application/x-ustar
vcd	application/x-cdlink
vda	application/vda
viv	video/vnd.vivo
vivo	video/vnd.vivo
vrml	model/vrml
wav	audio/x-wav
wrl	model/vrml
xbm	image/x-xbitmap
xlc	application/vnd.ms-excel
xll	application/vnd.ms-excel
xlm	application/vnd.ms-excel
xls	application/vnd.ms-excel
xlw	application/vnd.ms-excel
xml	text/xml
xpm	image/x-xpixmap
xwd	image/x-xwindowdump
xyz	chemical/x-pdb
zip	application/zip