Benefit of having a GPU for adding watermark using FFMPEG using x.264 My understanding is that GPU acceleration is not beneficial to encoding using x264.

The question is if there is any benefit to having a GPU if you are also adding a watermark.
GPU acceleration is beneficial to encoding; that is its main use. But it has no benefit with x264 which is entirely CPU-based.

There is a H/W overlay filter but the speed improvements are negligible, AFAIK, because of the memory ops transferring data to and from GPU memory. It's primary benefit is for when the entire pipeline is GPU-bound.