You might be interested to try this patch if you want to work on a video soundtrack with Ardour.
A more complex program is dedicated to this task (xjadeo), but if you know pd/gem ...
This patch has been used with pd-extended on ubuntu hardy.
You also need to compile jack_transport by Tim Blechmann (not included in Pd-extended at the time of writing), but present in the "externals" repository.

ps:
video format handling might be a little bit tricky.
with the help of mencoder, i finally used mjpg format for videos
/usr/bin/mencoder -nosound video_source.avi -idx -ofps 25 -ovc lavc -lavcopts vcodec=mjpeg -noskip -vf harddup -o video_target.mjpg