.JMV File Extension
What is a JMV file?
Gameplay recording created by Jnes, an NES emulator for Windows; saves the state of the NES ROM (.NES or .NSF file) as well as user inputs so that the exact gameplay can be replayed in the software; does not contain actual video data (i.e., no .AVI, .MP4, etc. file); can be shared with other Jnes users, who can watch the replay in Jnes.
NOTE: If you want to convert JMV files to an AVI movie, you can follow the steps in the Jabsoft movie recording tips article.