Can I choose the thumbnail for my uploaded video?

You will see the option to choose a video thumbnail on the 'upload complete' page in the 'single settings'.

Each video will present you with a selection of thumbnails you can choose from so you do not have to simply accept the one the system assigns during the upload process.

You will also see this option in the media manager, hit the video upload you wish to change the thumb of and you will see the option under 'settings' for that particular video. Just hit the thumb you prefer and press 'ok'.