When Tsunami was updated for Vegas 5, I used the new feature in Vegas 5 – sub-clips. Some other people mentioned this as well so when the tools were moved to and updated for Excalibur 4, I added an option to use sub-clips OR simply copy like the Vegas 4 version. So… Excalibur 4 will do what you are wanting.
As for the current situation, the only way I know to extend the sub-clip is to actually use the trimmer.
Edward Troxel
