Convert WBM to MP4

We are not aware of any existing way to convert WBM files directly to MPEG-4 Videos (.wbm to .mp4 conversion).

Perhaps this is just a typo, and you are actually searching for ways to convert WebM Videos to MPEG-4 Videos. In that case, please refer to the WEBM to MP4 conversion entry.

Simply put, it is impossible to convert WBM to MP4 directly.
Thus, there is no so-called wbm to mp4 converter or a free online .wbm to .mp4 converter to be found.