This option is available from Project Menu. However, most of the time it appears to be greyed out. I only find is non-grey on a clip that has just been added to the Project Tree.
And if I select the Edit Clip menu item - nothing appears to happen. So I dunno what this item does or is supposed to do.
I ask this because I have been doing a heap of work on the kdenlive manual at http://userbase.kde.org/Kdenlive/Manual. I am trying to get a page for every menu item. So this means going through the whole application. A lot of work but I sure know a lot about bits of Kdenlive I never knew about before.
Come over and contribute if you want !