'Preview' thumbnails vs. Icon on video files?

[npriess]

Hi,

I have a bunch of almost similar .mkv files. On some of them, I see the MPlayer OSX logo which I use for playback. But on most of them a preview from the video is shown as the icon... Why is that?

 

[BlueRevolution]

Thumbnails are generated with QuickTime. If QuickTime can't play the file, Finder can't generate a thumbnail.