[Cin] h264 vulkan encoding

A patch brings hardware encoding with vulkan into ffmpeg. In the future I will try to make a preset for h264, but if I understand correctly you have to use the ffmpeg from Lynne's repository and then compile it with the --enable-vulkan option. Do you think a simple replacement of our ffmpeg tar.gz with Lynne's tar.gz is enough? https://lynne.ee/vulkan-video-encoding.html