In case that your .vdata file from Vaulty app are actually a 3GP video, you can simply rename vdata to 3gp. This is because the software does not alter or encode your video, so just chaning the file extension from vdata to 3gp should be enough. Except for that, we have no information about any program that would be capable of direct vdata to 3gp conversion.
Open VDATA file Open 3GP file