By default, Imagevue creates thumbnails(previewimage) automatically for image files like JPG, PNG and GIF. Unfortunately, Imagevue can not create thumbnails for other filetypes like MP4,FLV, DOC or PDF. Instead, it creates generic thumbnails that simply indicate the nature of the file. See examples:
FLV
DOC
PDF
MP4
Create custom thumbnail
If you want to create your own thumbnail for a specific file, you can simply create a file "tn_filename.jpg". For example, if you have a video file called "myvideo.mp4", you can create a thumbnail for that file called "tn_myvideo.jpg".
Create custom generic thumbnail
If you want to create a generic thumbnail graphic that applies for all thumbnails of a specific filetype, you can simply edit or replace the default files under imagevue/images/thumbs/.