A small heads-up for the new world of (X)Wayland we are about to enter: in a Wayland session on Fedora 25, the menu bar in Avidemux steals focus from Ctrl+Up (seek 60 seconds forwards) and Ctrl+Down (seek 60 seconds backwards), these shortcuts simply open the File (or any other if the Tab key was pressed before) menu.
The workaround is to open and to close a modal dialog without menu bar like the Go To Time dialog (Ctrl+T) prior to using Ctrl+Up or Ctrl+Down. Resizing the Avidemux window transfers keyboard focus back to the menu bar.
The issue doesn't exist in a Xorg session, and there is hope that the bug gets fixed by chance in Fedora prior to the release.