Quicktime player not referencing mp4 files

[stgoldberg at aol.com]

I'm using Livecode 5.5.2 and note that the Quicktime player, while able to reference .mov files, cannot reference .mp4 files (or AVI files).  However, previous versions of Livecode did reference .mp4 files.  Has there been some change in the more recent version of LiveCode?  Thanks.
Steve Goldberg
www.medmaster.net