Gorp
Easy Video Editor - graphical interface to non-linear video editor
...Currently it can read and write MPG1 and MPG2 files, and transform them on the way. The number of transforms available is limited, but will grow.
View the video flow at any part of the flow diagram, step forward, backward etc to make sure that it is correct.
Write your own transforms in javascript and run them in gorp - complete with persistence to file, and parameter editing/checking through the GUI.
Your work is saved as a text-based script - furure tools will allow direct scripting.