For this process without any optimization, the process ran for 94 seconds and produced an encoded file with the size of 389 MB (18.4% smaller). Theoretically, from H.264 to H.265, one would expect the file size to be cut in half. I am not seeing a half of reduction here. In fact, it is 32% away from being 50%. Thus, the early conclusion here is the GPU transcoding through the nvenc library is not as efficient as the CPU encoding.