feat(grain): grain_sigma/grain_flat metadata — the tune=auto detection enabler (ADR-0142)#43
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…ection enabler (ADR-0142) The session's measurement campaign established the law: NVENC is genuinely worse than x265, but the pre-encode gain that closes it is REDUCTIVE and CONTENT-DEPENDENT (additive pre-sharpen washes; denoise scales with removable grain; clean content gains ~0), and mostly a matter of TUNING. So there is no single best filter -- there is a tuned reductive boost per content class and a router (tune=auto) that detects the class from analyze.* metadata and applies it. The router needs content detection that did not exist: grain_estimate computes per-band RMS residual but emitted zero frame metadata (trapped in the PEL_SEC_FILMGRAIN side-data). This ships the first and highest-leverage enabler: grain_estimate now emits lavfi.pelorus.grain_sigma (peak per-band RMS over the edge-gated flat bands -- structure excluded by construction, so what survives is grain stddev) and lavfi.pelorus.grain_flat (the flat fraction = confidence), via the ADR-0136 av_dict_set pattern. No interop ABI change, no shader change, the value was already computed; the side-data path is untouched. Verified discriminating (heavy-grain 0.019 vs clean-ish Bluray 0.012) and unblocks the proven -34% grainy denoise route. ADR-0142 records the full tune=auto design (8-class routing table + validation priority + the encoder-integration patch parallel track). Follow-ups: the remaining detection enablers (noise_sigma, dark_frac), the per-leg validations, the router itself, and the encoder-patch track. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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What
The foundational first step of
tune=auto(the content-adaptive pre-encode router):vf_pelorus_grain_estimate_vulkannow emitslavfi.pelorus.grain_sigmaandlavfi.pelorus.grain_flatas per-frame metadata, so the router can detect grainy content. ADR-0142 records the full design.Why (the law this session established)
With the real tooling (vmaf v1.0.16 + v0.6.1-NEG, x265-enabled ffmpeg, on-hardware NVENC): NVENC is genuinely worse than x265, but the pre-encode gain that closes it is REDUCTIVE and CONTENT-DEPENDENT.
→ There is no single best filter, there's a tuned reductive boost per content class + a router. That router needs detection metadata that didn't exist (only
analyzeemitted any).The enabler
grain_estimatealready computes per-band RMS residual over edge-gated locally-flat pixels (structure excluded by construction → what survives is grain stddev) but trapped it in thePEL_SEC_FILMGRAINside-data. This emits the peak asgrain_sigma+ the flat fraction asgrain_flat(confidence), via the ADR-0136av_dict_setpattern — no interop ABI change, no shader change, the value was already computed; the side-data path is untouched. Verified discriminating: heavy-grain clip 0.019 vs clean-ish Bluray 0.012.ADR-0142 (Proposed) records the full design
The 8-class routing table (grainy→denoise, anime→dehalo+aa+deband, textured→spatial-denoise, re-encode→demosquito, dark→dark-masked-denoise, screen→deblock, sports→denoise+mc-warp, clean→no-op), the validation priority (grainy scaling first — the proven lever; every leg iso-bitrate-proven + held-out-confirmed before it enters the router), the constraints (analyze.texture is derived; motion needs upstream mc), and the encoder-integration patch parallel track (NVENC/QSV/AMF features FFmpeg underuses).
Deliverables
Filter (metadata only) + ADR-0142 + README index +
grain_estimate.mdmetadata section + changelog + regenerated patch 0006. No ABI/shader/surface-behavior change beyond the additive metadata.🤖 Generated with Claude Code