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vmaf-tune --coarse-to-fine

vmaf-tune corpus --coarse-to-fine runs the ADR-0306 two-pass CRF search instead of enumerating a full manual CRF grid. It is useful when the operator has a target VMAF and wants the corpus rows needed to pick the smallest acceptable bitrate without scoring every CRF in the codec range.

The implementation lives in tools/vmaf-tune/src/vmaftune/corpus.py::coarse_to_fine_search and is wired through tools/vmaf-tune/src/vmaftune/cli.py.

How It Works

  1. Coarse pass: score a wide CRF sweep such as 10,20,30,40,50.
  2. Pick the coarse cell closest to --target-vmaf.
  3. Fine pass: score a narrow window around that cell.
  4. Emit the union of visited rows to the normal Phase-A JSONL schema.

With defaults, one source/preset visits up to 15 CRFs instead of a full 0..51 sweep:

vmaf-tune corpus \
    --source ref.yuv \
    --width 1920 --height 1080 --pix-fmt yuv420p \
    --framerate 24 --duration 10 \
    --encoder libx264 \
    --preset medium \
    --coarse-to-fine --target-vmaf 92 \
    --output corpus_c2f.jsonl

Flags

Flag Default Notes
--coarse-to-fine off Enables the two-pass search for corpus; recommend uses it by default.
--target-vmaf — Target used to centre the fine pass.
--coarse-step 10 CRF spacing for the coarse pass.
--fine-radius 5 Half-width around the best coarse CRF.
--fine-step 1 CRF spacing inside the fine window.

Output

Rows are ordinary vmaf-tune corpus rows. Downstream consumers do not need a separate parser; recommend, predictor training, and Phase-B bisect tooling can consume the JSONL as usual.

See Also