There is a bug with the new multimedia filter (from Moodle 1.8) with *.mp3 or *.swf files.
When such files are linked from a "composed Web page" within a Moodle course, it works OK.
But when such files are linked from an HTML uploaded file in the course files neither the moodle mp3 player nor the flash player are displayed.
From what I can gather, the "new Javascript system" does correctly write the necessary <object></object> code in the html file before displaying it FOR A COMPOSED WEB PAGE, but it does not write it to the HTML uploaded file.

Example with file audio.mp3:
in composed Web page we get this:
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Click <a href="http://localhost/moodle18dev/moodle/file.php/2/course/audio.mp3">here</a><span style="visibility: visible;" class="mediaplugin mediaplugin_mp3" id="filter_mp3_11871632651"><object data="http://localhost/moodle18dev/moodle/filter/mediaplugin/mp3player.swf?src=http://localhost/moodle18dev/moodle/file.php/2/course/audio.mp3" type="application/x-shockwave-flash" height="15" width="90"><param value="high" name="quality"><param value="bgColour=000000&amp;amp;btnColour=ffffff&amp;amp;btnBorderColour=cccccc&amp;amp;iconColour=000000&amp;amp;iconOverColour=00cc00&amp;amp;trackColour=cccccc&amp;amp;handleColour=ffffff&amp;amp;loaderColour=ffffff&amp;amp;waitForPlay=yes" name="flashvars"></object></span>
<script type="text/javascript">
//<![CDATA[
  var FO = { movie:"http://localhost/moodle18dev/moodle/filter/mediaplugin/mp3player.swf?src=http://localhost/moodle18dev/moodle/file.php/2/course/audio.mp3",
    width:"90", height:"15", majorversion:"6", build:"40", flashvars:"bgColour=000000&amp;btnColour=ffffff&amp;btnBorderColour=cccccc&amp;iconColour=000000&amp;iconOverColour=00cc00&amp;trackColour=cccccc&amp;handleColour=ffffff&amp;loaderColour=ffffff&amp;waitForPlay=yes", quality: "high" };
  UFO.create(FO, "filter_mp3_11871632651");
//]]>
</script> to listen.
------------------------------
in HTML uploaded page we get this:
Click <a href="audio.mp3">here</a><span class="mediaplugin mediaplugin_mp3" id="filter_mp3_11871623921">(MP3 audio)</span>
<script type="text/javascript">
//<![CDATA[
  var FO = { movie:"http://localhost/moodle18dev/moodle/filter/mediaplugin/mp3player.swf?src=audio.mp3",
    width:"90", height:"15", majorversion:"6", build:"40", flashvars:"bgColour=000000&amp;btnColour=ffffff&amp;btnBorderColour=cccccc&amp;iconColour=000000&amp;iconOverColour=00cc00&amp;trackColour=cccccc&amp;handleColour=ffffff&amp;loaderColour=ffffff&amp;waitForPlay=yes", quality: "high" };
  UFO.create(FO, "filter_mp3_11871623921");
//]]>
</script> to listen.
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I have checked in the Admin pages that my filters are ON, and Filter uploaded files is set to HTML files only. I have also checked that there is no path problem.

This is very urgent and important, as our university has upgraded from 1.6 to 1.8, we have a lot of mp3 files linked in our HMTL uploaded files and we do need this pb to be solved for the September new year.
Thanks in advance,
Joseph