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Export: convert H.264 frames to YUV 4:2:0 on the GPU - #1631
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Accelerator::comp_frame_yuv420 (default None) renders a top-level comp frame and converts it over the background to the H.264 export's 8-bit BT.709 limited-range 4:2:0, every byte within one level of the CPU conversion (the GPU kernel follows it operation for operation, including NaN and half-away-from-zero ties, but a driver may contract its arithmetic). A 4K frame then reads back 12 MB of planes instead of 133 MB of RGBA f32. The H.264 export asks the accelerator for planes when a frame needs nothing after the render (progressive, project depth, no crop/resize, rendered at the output size) and otherwise renders and converts on the CPU as before. Deferred readbacks (a browser worker) keep the pass-based path. Sizes the kernel can't take (width not a multiple of 8, odd height) are declined before any GPU work. rgba_to_yuv420 moves to effectcraft_raster::yuv so the export and the GPU tests share one reference. The GPU tests are #[ignore]d and fail without an adapter instead of passing untested.
This was referenced Oct 16, 2026
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Tested on AMD: RX 6900 XT, Windows 11, Adrenalin 32.0.21045.5002, Vulkan, All 6
Odd sizes fall back to the CPU, and unsupported sizes are declined as expected. Whole Generated with Claude Code |
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YUV part of #898, split out.
With the GPU on, H.264 export reads every frame back as RGBA f32 and converts to 4:2:0 on the CPU. At 4K that's ~133 MB per frame back for ~12 MB of planes. This does the conversion in a small compute kernel and reads back only the planes.
Accelerator::comp_frame_yuv420, defaults toNone. The GPU compositor implements it.None, it's the old RGBA path. Deferred readbacks (browser worker) keep their path. Sizes the kernel can't do (width not a multiple of 8, odd height) are rejected before rendering.rgba_to_yuv420moved from export toeffectcraft_raster::yuvso export and the GPU tests share it.GPU output is within one level of the CPU conversion. llvmpipe matches exactly; on an RTX 3090 (Vulkan) ~0.25% of bytes come out one level off, probably FMA contraction / divide precision in the driver. Tests require exact on software adapters and allow ±1 on a small fraction elsewhere.
Tests:
yuv420_matches_cpu(noise, NaN/inf, out-of-range, a few sizes)rounding_ties_match_cpu(every Y tie, plus U/V ties)comp_frame_yuv420_is_the_cpu_conversion_of_comp_frame,odd_sized_comps_fall_back_to_the_cpu,unsupported_sizes_are_not_convertedexport/tests/h264_gpu_yuv.rs(fake accelerator, checks the wiring, fallback and deferred path)GPU tests follow the crate's usual
tests::gpu()pattern and skip without an adapter.Tested on llvmpipe and an RTX 3090 (Vulkan). DX12 on that card fails to create the context on main already (
classic3d: Validation Error), separate issue. fmt/clippy clean; only the two known main failures (tests_fx_pixel2::stylize,tests_fx_stylize::posterize_thresholds_strobe_vignette).Async version is #1632, on top of this.