There is only one file type that uses the .XEL extension:
Expression Encoder Live Encoding File
Settings file created by Expression Encoder, a video transcoding application included with Microsoft Expression Studio; stores the presets for a live video encoding session and includes references to the source media as well as the transcoding settings for each file; saved in an XML format.
Live encodings are performed while video is streaming. For example, a XEL file can save settings for encoding a live webcast into a video stream or file. Live encodings differ from encoding jobs, which are saved in the .XEJ format.
Expression Encoder is available for free or as part of Microsoft Expression Studio. However, Microsoft discontinued Expression Studio in 2012.
Updated: March 29, 2020