I had just built one of my tutorials and I went to editing, tried to trim the clip and it freezes at around 90%. Minecraft stops responding after a few minutes of staring at a frozen screen. I re-opened Minecraft my file was not trimmed and it does not show up for me to edit the clip. I also thing the controls are somewhat difficult to use at the moment.
_Just
Don't you think it'd be a good idea to upload the original file and state your trim parameters so we can test it ourselves and debug it? Otherwise nothing's going to change.
// Edit // And you might want to post the exception(s) printed in the log as well (if there are any).