forked from unom/punktfunk
enricobuehlerandClaude Fable 5
9f72a3b6ad
An HDR display cost you full chroma: the IDD-push capturer's only 10-bit
output was P010, so a session that negotiated 4:4:4 on an HDR desktop was
converted to 4:2:0 at capture time — *after* the Welcome had already told
the client 4:4:4. The client believed it (nothing on the wire contradicts
a Welcome), and the new chroma tag in the stats overlay is what finally
made the discrepancy visible.
Everything except the source was already in place, which is why this is
small: the NVENC config layer has stamped `FREXT` + `chromaFormatIDC=3` +
`pixelBitDepthMinus8=2` — HEVC Main 4:4:4 10 — with a unit test since the
4:4:4 work landed, `PixelFormat::Rgb10a2` already maps to `ABGR10` and
already counts as a full-chroma input, and the desktop client learned the
10-bit 4:4:4 Vulkan pool format in 74863c96. The one missing piece was a
capture format that keeps 10 bits AND full chroma.
`HdrRgb10Converter` is that piece: one full-res pass from the FP16 scRGB
desktop to packed `R10G10B10A2` in BT.2020 PQ, reusing the P010 shader's
`scrgb_to_pq2020` verbatim so both HDR outputs share bit-identical colour
math — it simply stops before the RGB→YUV matrix, the studio-range
squeeze and the chroma decimation. NVENC then does the CSC to YUV 4:4:4
itself under FREXT, exactly as the SDR BGRA passthrough has always done
at 8 bits.
No swizzle is involved and that is worth stating, because it looks like
it should be: NVENC names packed formats from the MSB down, so its
`ABGR10` (A2B10G10R10) puts R in the low 10 bits — bit-identical to DXGI
`R10G10B10A2_UNORM`. It is the same relationship the proven SDR pair
relies on between DXGI `B8G8R8A8` and NVENC's `ARGB`.
The honesty gap closes as a consequence: `capturer_supports_444` no
longer has a depth it cannot serve, so the chroma resolved before the
Welcome is the chroma the wire carries. AV1 is deliberately untouched —
Range Extensions are HEVC-only and no consumer encoder does AV1 4:4:4.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>