A 2026-08-12 field report (RTX 5060 client): every HEVC session demoted to
D3D11VA with 81 "outside device caps: stream level (Std code point 12) above
the device's maxLevelIdc (H.265 Std level 11)" refusals — the host's AMF
encoder stamps general_level_idc 6.2 (the codec maximum) on a 4K120 stream
that needs 5.2, and NVIDIA's driver caps H.265 decode at 6.1. The hardware
decodes the actual stream trivially; only the declaration was oversized.
AV1 passed the same gate, which is why "native-vulkan runs only with AV1".
The declared level is a claim, and the stream's real demands are enforced
where they are physical facts — coded extent and DPB depth, both checked at
session build. So the up-front level gate (H.264 + H.265) now warns once and
proceeds, and every SPS/VPS handed to the Vulkan parameters object has its
level clamped to the device ceiling (a set above maxLevelIdc is invalid
usage). AV1's gate is untouched: its code space is the bitstream's own and
no over-declaration has been seen in the field.
Verified on .173 (RTX 4090, driver 610.88): HEVC and AV1 both decode on the
native Vulkan rung at 60 fps against an NVENC host; unit tests pin the clamp
(lowers, only lowers, mutates the driver-visible block in place).
enricobuehler
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