Hey supercool,
When you upload media to Shotgun, we automatically generate a thumbnail for it. In the case of a movie file, the static thumbnail is usually a frame taken from the middle of the clip. If you want a different frame, you’d need to upload it to the thumbnail field directly, after the transcode had taken place (so it doesn’t get overwritten by the transcoder output).
Being able to specify which frame you want as the static thumbnail could be a handy feature. I’d recommend letting our product team know how you’d want something like that to work: