Recently I found a video on the net ( a .mp4 file), and when I had it on my computer with Windows7, I noticed its thumbnail was not the average windows 7 video thumbnail (which looks like a piece of video film with a random picture from the movie), but a custom thumbnail!
Looking in the file properties did not help find the correct button to change the thumbnail, so I just wonder how he did it! Here is a picture:
left: the custom thumbnail, right: the average thumbnail...
This is similar to the meta information used by mp3 sound files to add album art. By default, video editors use the default format you show on the right. But you can either specify the still image in the video editor or with a separate ID3 editor. Basically these editors let you modify a bit more attributes than right clicking the file and picking "properties" to change the title, artist, etc. Search for "MP4 ID3 tag editor" to find lists of available software.
This app also does it great.
Mp3 tag editor. Just drag the file to it, and you can edit all metadata, including the thmbnail/album art.
Its meant for Mp3 files, does a great job at that, but also works great for MP4 files.
VLC does it easily: Tools > Media Information > R-Click in thumbnail > add cover art from file.
