[Cin] h264 vulkan encoding

[Andrea paz]

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