[FFmpeg-devel] [PATCH] lavfi: add a libplacebo filter

[Niklas Haas]

On Tue, 09 Mar 2021 22:53:18 +0100 Lynne <dev at lynne.ee> wrote:
> Sorry, as we discussed on IRC the Vulkan hwcontext should be
> improved first and this filter should be kept as a pure hardware
> filter.

I changed my mind on this because:

- I think it's reasonably self-contained as is, and actually simpler to
  implement this way.

- There's no duplication of code within this patch.

- Sharing the VkImages directly is simply not a good approach. It
  creates an unnecessary API hassle (as demonstrated by the multitude of
  solved and unsolved issues surrounding device negotiation,
  synchronization, etc.)

- Therefore, it's better to share using an agreed-upon mechanism like
  a shared memory object exported/imported using the Vulkan API.

- A good API for this already exists (dmabufs).

- You can already derive a drm device from a vulkan device and export
  vulkan hwframes as drmprime frames.

I plan on adding support for drmprime frames to this filter, which I
think is the cleaner way to avoid the upload/download. But I wanted to
get feedback on the current version, since it's *functionally* complete
as-is.

If you're worried about dmabufs being a Linux-only API, I would still
rather see an approach based on Vulkan memory object imports/exports
rather than attempting to share and synchronize the VkImages directly.

Even just the fact that we can't each enable extensions/features we want
enabled independently is a reason that trying to share a single vulkan
device is a bad idea. Right now the result of that is that vf_libplacebo
atop hwcontext_vulkan would simply be missing out on features and
performance, compared to this version.