On 10/10/2024 10:50, martin schitter wrote:
On 10.10.24 08:06, Lynne via ffmpeg-devel wrote:You can copy libavutil/vulkan* into whatever project you want, and change 4 #include lines to make it compile. This lets you use the same API to construct and execute shaders as you would within lavc/lavfi/lavu into your own project. You will need to make libavutil a dependency as hwcontext_vulkan.c cannot be exported and must remain within libavutil.Thanks for this description and the link. It's very interesting but not exactly the kind of utilization I'm looking for.I don't want to use the ffmpeg vulkan utils in another application, as demonstrated in your example. I just want to use it within ffmpeg itself, but slightly different as in all places which I saw until now.To bring it to the point:I would like to accelerate this trivial 10 and 12bit decoding of bit- packed-scanlines in my DNxUncompressed implementation using compute shaders, whenever the required hardware support is available resp. was enabled on startup and fallback to CPU processing otherwise.This is a different usage scenario than utilizing the hardware encoding and decoding facilities provided by vulkan, which seem to be the only kind of vulkan related GPU utilization in libavcodec until now.And because it should be used automatically if available and otherwise fall back to CPU processing it also differs significantly from the vulkan- and placebo filters, which are strictly divided from their CPU counterparts and don't provide any fallback.I simply couldn't find any location in ffmpegs source code, which looks close to this vague idea. Perhaps it's simply impossible for one or the other reason that I do not see -- who knows?I would be happy if you could possibly point me to already existing relevant code in ffmpeg to learn how to develop this kind of behavior as efficient as possible.
Petro Mozil wrote a Vulkan VC-2 decoder that'll soon get merged: https://github.com/pmozil/FFmpegIts an example on how to accelerate via compute shaders. What he did was he simply introduced vc2_vulkan as a hwaccel. It makes sense, even for partially accelerated codecs, since the hwaccel infrastructure handles everything for you, **including a fallback for CPU decoding**, and users automatically get accelerated support.
Generally, the flow should be exactly the same as with vulkan_decode.c for video - but instead of writing decoding commands in the command buffer, you run a shader. (this is just an example, vulkan_decode.c is for Vulkan video decoding in specific, you shouldn't use that bit of code, just like Petro didn't).
If you need help, IRC, as usual.
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