iTunes: How to set the poster frame of movies
A "poster frame" is a still image of a movie that appears as the movie's icon in the Videos playlist. The default poster frame is the first frame in the movie.
To change a movie's poster frame:
- In iTunes, play the movie in a separate window (not in full screen or the main window).
- Drag the playhead to the desired frame.
- Right-click (or Control-click) the movie window, and from the shortcut menu, choose Set Poster Frame.
Note: You can only change the poster frame of videos you import. You can't set the poster frame of videos purchased from the iTunes Store, muxed (multiplexed) videos including MPEG-1 and MPEG-2 files, and 3GP videos.