[Libav-user] Libavcodec D3D12 hevc_nvenc

[Ben Harper]

I don't have any experience with D3D12 video encoding, but I can tell you
that all the encoding APIs are quite similar, and with the assistance of AI
tools, you can usually get through the initial slog of learning the API
very quickly.
I'm not sure what you mean by "hevc_nvenc doesn't list d3d12 as a pixel
format supported". Pixel formats are things like DXGI_FORMAT_R8G8B8A8_UNORM
or NV12. If the hardware encoder doesn't support your pixel format, there's
always a way to convert it, either with some CUDA code, or libyuv on the
CPU. I agree that doing it all through ffmpeg is the best route if it works
for you.

On Wed, 9 Jul 2025 at 18:31, Alex Cha <alex-1er-at-hotmail.com at ffmpeg.org>
wrote:

> Thank you for your quick response!
>
> Yes, that was the way we were going to investigate next, we already had a
> project using Nvenc directly, but the original implementation was for
> OpenGL.
> We also saw there was D3D12 Video Encoding (D3D12 Video Encoding |
> DirectX-Specs
> <https://microsoft.github.io/DirectX-Specs/d3d/D3D12VideoEncoding.html>)
> that might also do something similar. Do you have any experience with the
> latter? Otherwise we'll most likely do as you say with the nvidia SDK.
>
> I was contacting for low latency as that is currently the problem I was
> having, however the reason we wanted libavcodec initially is that a few of
> our clients cannot agree on a codec. So we wanted the broad range of codecs
> supported by FFmpeg, even if that meant a higher latency. I thought we
> could do a basic implementation, test the end-to-end latency and figure out
> from there if we needed a lower level implementation. It is only while
> doing the implementation that I found that even though d3d12va is
> supported, the hevc_nvenc doesn't list d3d12 as a pixel format supported.
> ------------------------------
> *From:* Libav-user <libav-user-bounces at ffmpeg.org> on behalf of Ben
> Harper <rogojin-at-gmail.com at ffmpeg.org>
> *Sent:* July 9, 2025 11:19 AM
> *To:* This list is about using libavcodec, libavformat, libavutil,
> libavdevice and libavfilter. <libav-user at ffmpeg.org>
> *Subject:* Re: [Libav-user] Libavcodec D3D12 hevc_nvenc
>
> Have you tried just using the nvidia SDK directly? Since you need low
> latency, I assume this is for some kind of realtime application, which
> implies you're streaming video packets. The raw video codec data is simpler
> than many people imagine. It's just a stream of packets - also called NALs,
> or NALUs. The nvidia encoder will likely spit these out, and I'm guessing
> this is what your decoding side needs. You'll want avcodec for packaging
> those up into a .mp4 file or some other container format. But if you're
> just streaming live video data, then I'm guessing you don't actually need a
> container file format, so the raw packets might be good enough.
>
> On Wed, 9 Jul 2025 at 17:12, Alex Cha <alex-1er-at-hotmail.com at ffmpeg.org>
> wrote:
>
> Hi,
>
> I was under the impression that there was hardware acceleration for D3D12
> supported by ffmpeg.
> Upon implementing the solution however, we had unsupported pixel format
> d3d12 by the hevc_nvenc.
>
> Digging further in the nvenc.c code it seems d3d12 format is not supported
> directly. Was there a reason for this? Looking into the nvidia
> documentation the encoder should support D3D12, even if it is unclear to me
> what needs to be done.
>
> For reference, we are trying to integrate hardware streaming using FFmpeg
> into a unreal engine 5 application which uses D3D12. We need a very low
> latency.
> We have tried using the D3D11on12 interop without success, it is returning
> us "openencodesessionex failed no encode device(1)". The adapter seems to
> be using my RTX 4090 correctly but no success.
>
> Anyway, this email is a long shot in case someone as already encountered
> these issues and is able encode without copying to CPU.
>
> Thanks,
> Alex
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