Algorithm to create a unique URL for OU audio-visual (OU podcast tracks), version 1 / 24 November 2010.

oupod-algo.php

<?php
/* Algorithm.
*/
ini_set('display_errors', 1);
header('Content-Type: text/plain');
?>
/*
 Algorithm to create a unique URL for OU audio-visual (OU podcast tracks), version 1.
 (N.D.Freear, 24 nov 2010.)
  
 Aims:
   - To create a fairly short, friendly, unique URL for a HTML 'page' for each track or AV asset.
   - To NOT be affected by a new podcast track being added to the 'start' of the list.
   - To be agnostic to the container format/extension (ie. .M4V versus .OGV; .MP3 versus...)
   - To be agnostic to the particular 'view' of the asset (ie. video versus transcript).
   - To not be dependent on the actual location of the asset (eg. MP3 file).
*/

<?php
$enclosure_url =
  'http://podcast.open.ac.uk/feeds/l1314-spanish/l1314audio1.mp3';
$transcript_url=
  'http://podcast.open.ac.uk/feeds/l1314-spanish/transcript/l1314audio1.pdf';

$album_permalink = 'http://podcast.open.ac.uk/pod/l1314-spanish'; #Check!
$album_canonical =
  'http://podcast.open.ac.uk/oulearn/languages/spanish/podcast-l1314-spanish';

$basename = basename($enclosure_url);
$no_ext   = preg_replace('/(.*)(\.\w+)/', '$1', $basename);

$md5_noext = md5($no_ext);
$md5_sub8  = substr($md5_noext, 0, 10);


$unique_1 = "$album_permalink/$md5_sub8";
$unique_2 = "$album_permalink#!$md5_sub8";

$unique_3 = "$album_canonical/$md5_sub8";
$unique_4 = "$album_canonical#!$md5_sub8";


$output =<<<EOF
# The location of the enclosure/ transcript may change.
enclosure_url  = $enclosure_url
transcript_url = $transcript_url

# This URL is unique for an album, and stable.
album_permalink= $album_permalink

# And this URL is where a user typically browses to - its unique and fairly stable!
album_canonical= $album_canonical


# 1. Get the filename.
basename  = $basename

# 2. Remove the file extension.
#  (We don't care if the file is .M4V or .OGV; .MP3 or...)
#  (Note, this would be the same if we used the transcript_url.)
noext     = $no_ext

# 3. Take the MD5 hash of noext.
md5_noext = $md5_noext

# 4. MD5 is too long - is it OK to take the first 10 characters? *
md5_sub   = $md5_sub8

# 5. Append the MD5 sub-string to the album permalink - should we support both '/' and '#!' ? **
unique_1  = $unique_1
unique_2  = $unique_2

# 6. Append the MD5 sub-string to the 'canonical' album URL - again '/' and '#!'. **
unique_3  = $unique_3
unique_4  = $unique_4

# 7. If later we wished to create YouTube-style deep-links, we could do this (that is, seek 1 minute 20 seconds into audio/video).
deeplink = $unique_2/t=1m20s

EOF;
echo $output;
?>


*  The hashes used for Mercurial/hg changesets/revisions are 12 characters.
** For points 5/6, see Google's idea for AJAX and search engine friendly links.

--