It looks like that wve to mp4 conversion is generally related to two different conversion that deal with the same thing, i.e. export of a project to a finished multimedia file. This is only possible if you also have the original multimedia data referenced in the project, without them it will be impossible to recreate the video.
The most likely wve to mp4 conversion scenario is export of Wondershare Video Editor projects (.vwe) to MPEG-4 video (.mp4). As far as we know you will need the original software, but the successor product - Filmora may also be of the here, especially if you are on macOS.
In essence, the very same thing like the previous wve to mp4 conversion, just for the Cyberlink PowerDirector.
It is worth mentioning that the free (trial) version of Wondershare software leaves a watermark on the video. The only legal way to do this is to use upgrade (pay) for the full version of the program. There is no way to convert wve to mp4 without watermark using some 3rd party software. Although you can find creative ways on internet when dealing with the problem how to remove filmora watermark.
Updated: April 13, 2017
Articles and other information relating to wve into mp4 conversion:
What is WVE file, how to open and convert it - Detailed information about Wondershare Filmora .wve project files