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.

In a word, direct wbm to mp4 conversion is not possible.
So don't expect any so-called wbm to mp4 converter or wbm to mp4 free online conversion tool available.