Verified against nvEncodeAPI.h's own splitEncodeMode doc (user-prompted
— the audit's 'exclusive for HEVC' one-liner deserved checking):
- H.264: split 'is not applicable' — hard-DISABLE the mode so the
written config, CeilingKey, the split diagnostic log and the
rejection-retry stay truthful (the retry used to re-open a
byte-identical session after an H.264 'split rejection'). The libav
path's operator arm gains the codec gate its auto arm always had.
- HEVC: split 'not supported if … subframe mode' — when WE force split
(TWO/THREE/AUTO_FORCED, the 4K120 throughput lever), sub-frame yields
with a logged escape (PUNKTFUNK_SPLIT_ENCODE=0 chooses sub-frame).
⚠ Keyed on FORCED modes only, never != DISABLE: AUTO(0) is the
resolver's fallthrough for every sub-950Mpix session, and the wider
key would have disarmed the Phase-3 chunked-poll feature fleet-wide
(critic catch). Under AUTO the driver arbitrates — the shipped state.
- AV1: untouched — per-tile sub-frame + split are legal together.
The arbitration is a pure nvenc_core fn called by each backend BEFORE
the ladder, the ceiling key and the chunked-poll latch — all three see
the post-arbitration truth. A drop inside build_init_params would have
left poll_chunk busy-polling its whole budget every AU (numSlices stays
0 without reportSliceOffsets; both loop exits dead — critic catch).
Linux latches subframe_forced beside subframe_on at query_caps (no env
re-reads after open); Windows records the arbitrated state so
reconfigure presents exactly the params the open had (also closes the
pre-existing mid-session env-flip hazard there).
Truth-table tests in nvenc_core; PUNKTFUNK_NVENC_SUBFRAME documented
(it never was); PUNKTFUNK_SPLIT_ENCODE row updated.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
enricobuehlerandClaude Opus 5
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