Thanks for your report.
Something has probably gone wrong with a previous install.
You can solve this by running the following command:
sudo apt-get install --reinstall avidemux
Let us known if this fixes your problem.
** Changed in: avidemux (Ubuntu)
Status: New = Incomplete
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** Attachment added: Dependencies.txt
http://launchpadlibrarian.net/18252687/Dependencies.txt
** Attachment added: DpkgTerminalLog.gz
http://launchpadlibrarian.net/18252688/DpkgTerminalLog.gz
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package avidemux 1:2.4.3-0.0ubuntu1 failed to install/upgrade: package avidemux
is already
