Issue details:

The filter_mediaplugin_ogg_callback(...) and filter_mediaplugin_ogv_callback(...) methods in filter/mediaplugin/filter.php reference the html_writer class, which is not defined in Moodle 1.9.10+ (build 20101103). This causes a fatal PHP error when those methods are called.

Solution details:

We added this custom class:

/usr/share/php/html_writer.php:
<?php
class html_writer {
function link($url, $text)

}
?>

(/usr/share/php is in our installation's include_path.)

Then we added this to our Moodle installation's config.php:

require_once 'html_writer.php';

We chose to write this code instead of fully backporting the html_writer class and other required functions from Moodle 2.0 because only this code appears to be needed at this time.