Add support for Vulkan encoding

[Lynne]

This issue tracks support for Vulkan encoding in FFmpeg. As the most used implementation of Vulkan decoding, its important that we implement Vulkan encoding to speed up adoption of the new standard for accelerated video.

Current development branch with all changes:

​https://github.com/cyanreg/FFmpeg/tree/vulkan

[Lynne]

H.264 encoder pushed.
And once the HEVC encoder patchset gets pushed, I'll close this issue.

[Mads Johansen]

I assume there's documentation coming as well?

[Lynne]

HEVC encoder merged.

Documentation is coming up tomorrow, but for now, you can use ffmpeg -help encoder=h264_vulkan and consult the VAAPI documentation since settings match.