I have come across a problem that is potentially a bug but would like to know if anyone else has the same issue before investigating further, I am running 2.5.1 so this may have been resolved since.
I have a forum where students are attaching short MP4 videos taken from a flip camera. In the media embedding options I have HTML5 video selected and Quicktime deselected and have the media filter enabled in the forum.
For Chrome and Firefox this works fine and the video attachment is replaced with an embedded HTML5 player version of the video itself. In IE10 and IE11 the embed is attempted but an error message stating "Error: Unsupported video type or invalid file path" is shown in the IE native HTML5 player.
The same file can be added to the content of a post in a forum and embeds properly and can also be added to the course as a file and plays fine to so the video itself is not the issue. After initial tests it seems the url itself moodle/pluginfile.php/77725/mod_forum/attachment/1767/VID00005.MP4 is not resolving as a valid url whereas moodle/pluginfile.php/77726/mod_resource/content/0/VID00005.MP4 does.