How to get file extension when renaming file with cffile

I'm using a cffile tag to upload my file and resave it with a new name. My issue is that the file could be a few different formats and I don't know how to detect the file extension. I'm using the code below:

<cfset ui = createUUID()>
<cffile 
  action="upload" 
  accept="video/x-flv, video/mp4, video/x-msvideo"
  destination="e:\www2\uploads\#ui#.#cffile.ServerFileExt#" 
  nameconflict="makeunique" 
  filefield="form.file"
>

It's telling me that cffile is undefined.