In sort of the the same vein as the excellent HamMultiPlayer, Kinovea is a specialized video viewer/player focused on slowing down and analyzing video for athletics/sports. It also includes some interesting edition features including export to a specific size, paused elements, and even export to a series of images.
An experimental portable version was posted in 2015: http://www.kinovea.org/en/forum/viewtopic.php?id=771
Status: Portable, writes to local folder ("\AppData")
License: GPLv2
Requires: dotNET 2.0+, WinXP+, 1024×600 monitor
Websites:
http://www.kinovea.org/
http://www.kinovea.org/en/downloads/
(I got this from a PA forum post.)