I don't know if you found a solution to the watermark problem yet but I had the same issue with video that I captured on an ATC2000 action camera. The camera used a compression codec that was somehow removed from my computer so any files that ended up in that codec wound up with the watermark on them.
There is a simple fix but I don't recall the detailed steps. What I did was googled the url that is appearing in the watermark with the words "remove watermark" This brought up a bunch of sites that had solutions. In my case I ended up going to the site shown in the watermark and in the support section of their website I was able to find the steps to fix the problem.
Deshpak (a.k.a Thundercat98 on Livevideo)