How to upload a 16x9 film?

Hey - my short is in 16x9 format.  It's small enough in pixels and in file size, but the ratio isn't 4x3.  Is there anything I can do, a masking program or something that I can use, to put the letterbox on my film so I can upload it?

Thanks

Hi amrench,

Your aspect ratio will be maintained when viewed in the player, with letterboxing added to the top and bottom. We recommend videos to be 4:3 to make use of all the space available.

Many Thanks,
Ady

Great!  Thanks for the quick reply.