I am no attorney, but it seems if you were involved in how
the artists performed their concert, you might be considered
as one of the creators of the artwork. But, if you simply
did or supervised the video taping, I doubt you would be
considered as a creator.
For example, if for some reason a movie company were to ask
you to video tape a movie in a local theatre, you did not have
part in the creation of the movie. However, if you were involved
in the directing as to how the movie was created, then it seems
you would be considered as a creator.
You might contact the person(s) for whom you worked, and ask
if they would be willing to sign a permission release, stating
under what circumstances you could show the video tapes.
An example of an "Artwork Permission Agreement" can be
found in the book titled "Getting Permission: How to License
& Clear Copyrighted Materials Online & Off" by Attorney Richard
Stim, which is available for purchase at
http://www.nolo.com