XnView Frame
From Just Solve the File Format Problem
XnView Frame (.xnf) is a file that contains a reference to an external video file, and a frame in that file. In most or all cases, it contains a snapshot image of that frame. It is associated with the XnView graphics software (at least XnView MP).
An XNF file can be created by playing a video file in XnView MP, pausing it, right-clicking on it, and selecting "Extract current frame" from the menu.
Format details
An XNF file is a standard JFIF/JPEG file containing a still image of the relevant frame. It also has embedded XMP+RDF metadata containing the video file's name, and a frame number. The metadata includes an attribute similar to the following:
xmlns:xnvmp="http://ns.xnview.com/xnf/1.0/"
There might be other XNF formats. The original proposal[1] was different.
Software
- XnView MP: Refer to XnView.