Running the same task on my workstation and letting the graphics card do the H.265/HEVC decoding + re-encoding in H.264 format is done at 13 times the original video frame rate, i.e. In other words, transcoding the video takes around 1.5 hours. Compressing a 49 minute 2.9 GB video file encoded with HEVC (H.265) and made on a mobile phone to a low bit-rate H.264 encoded video with a size of 380 MB is done at around 0,6 of the original video frame rate on my notebook. The speed-up that can be reached mainly depends on the input data and the desired output codec and quality. Since then I have found further parameter improvements for ffmpeg and in some scenarios, my speed-up is now over 30x compared to running the same task on my notebook. As I wrote at the time, I could get a speed-up of up to 8x over my X250 notebook. One of the reasons I bought a used Z440 workstation with a 6 core Xeon CPU and an Nvidia graphics card back in December was to offload and speedup occasional video transcoding tasks.

Ffmpeg hevc encoding