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feat(linux): zero-copy 4:4:4 — the EGL worker converts to planar YUV444 on the GPU

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A 4:4:4 session no longer falls to the CPU path (SHM capture + swscale
RGB→YUV444P + re-upload — the fps-ceiling triple tax). The zero-copy worker
grows a Yuv444Blit: three full-res R8 GL passes (the proven BT.709
coefficients; studio or full range per PUNKTFUNK_444_FULLRANGE, read by both
processes so pixels and VUI flip together) into ONE stacked 3-plane pitched
CUDA allocation — which keeps the worker↔host wire and IPC single-plane. The
encoder copies the planes into ffmpeg's yuv444p CUDA surface and hevc_nvenc
emits Range-Extensions 4:4:4 natively.

ImportKind::Tiled444 is APPENDED to the worker protocol (a worker outliving a
replaced host binary must keep the old tags stable; an old worker just errors
the import, which the fail machinery already handles). A 4:4:4 session on a
LINEAR/gamescope capture — no convert wired there — fails with a clear message
instead of letting hevc_nvenc silently subsample. caps().chroma_444 now keys
off the session (it missed the GPU path when keyed off the swscale's
existence).

Live-verified on the CachyOS VM (RTX 5070 Ti): per-frame "imported to CUDA
yuv444=true", stream Rext/yuv444p/bt709 in both tv and pc range, no CPU-path
warning.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
Enrico Bühler
2026-07-10 18:08:41 +02:00
parent 5f687a7083
commit 0dacb37088
13 changed files with 532 additions and 73 deletions
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crates/punktfunk-host/src/session_plan.rs
+13 -9
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@@ -124,22 +124,26 @@ impl SessionPlan {
pub fn output_format(&self) -> crate::capture::OutputFormat {
let gpu = self.encoder.is_gpu();
// Linux NVENC 4:4:4: libavcodec `hevc_nvenc` only emits 4:4:4 from a YUV444 *input* frame —
// RGB-in is always subsampled to 4:2:0 (verified on the RTX 5070 Ti). So the encoder does an
// RGB→YUV444P swscale and needs CPU-resident RGB frames; force the zero-copy GPU capture off
// for a 4:4:4 NVENC session. (VAAPI 4:4:4, where the hardware supports it, keeps its dmabuf
// path via `scale_vaapi`; Windows NVENC ingests ARGB directly and stays GPU.)
// RGB-in is always subsampled to 4:2:0 (verified on the RTX 5070 Ti). With zero-copy
// enabled the import worker produces that input ON the GPU (`ImportKind::Tiled444` — the
// planar-YUV444 convert), so the session stays fully zero-copy at full chroma. Without
// zero-copy the encoder swscales CPU RGB → YUV444P, which needs CPU-resident frames —
// force the GPU capture off for that case only. (VAAPI 4:4:4, where the hardware supports
// it, keeps its dmabuf path via `scale_vaapi`; Windows NVENC ingests BGRA directly.)
#[cfg(target_os = "linux")]
let gpu = {
let force_cpu_for_nvenc_444 =
self.chroma.is_444() && !crate::encode::linux_zero_copy_is_vaapi();
let force_cpu_for_nvenc_444 = self.chroma.is_444()
&& !crate::encode::linux_zero_copy_is_vaapi()
&& !crate::zerocopy::enabled();
if gpu && force_cpu_for_nvenc_444 {
// Surface the trade loudly: this is the single biggest per-frame cost a 4:4:4
// session adds (full-res CPU readback + swscale RGB→YUV444P every frame), and
// it looks like an unexplained fps ceiling if you don't know it happened.
tracing::warn!(
"4:4:4 session on the NVENC path: zero-copy GPU capture DISABLED — every \
frame is CPU RGB + swscale RGB→YUV444P; expect a lower fps ceiling than \
4:2:0 at this mode"
"4:4:4 session on the NVENC path without PUNKTFUNK_ZEROCOPY: zero-copy GPU \
capture DISABLED — every frame is CPU RGB + swscale RGB→YUV444P; expect a \
lower fps ceiling than 4:2:0 at this mode (set PUNKTFUNK_ZEROCOPY=1 for the \
GPU 4:4:4 convert)"
);
}
gpu && !force_cpu_for_nvenc_444