Adds an in-process evaluation suite covering native (SSIM/PSNR/LPIPS/
optical_flow), audio, physics_iq, vbench (16 sub-metrics), and
videoscore2. Public API: create_evaluator/evaluate, BaseMetric +
@register, ensure_checkpoint, get_cache_dir. CLI: fastvideo eval
list/run.
VBench upstream pinned as a git submodule at
fastvideo/third_party/eval/vbench (Vchitect/VBench@45e79ec); modern-dep
compat is achieved via runtime shims in vbench/__init__.py rather than
on-disk patches. CLIP/torch.hub caches are routed through
${FASTVIDEO_EVAL_CACHE}; HF cache stays at the system default.
ensure_checkpoint delegates to fastvideo.utils.get_lock + huggingface_hub
primitives. Evaluator supports release_cuda_memory(), unload(),
reload() for training-time eval that frees GPU between calls.
Verified parity against upstream vbench (5/8 metrics bit-exact, others
within 1% drift driven by transformers/torch version skew) and against
upstream VideoScore2 (regex anchored on the actual model's output
format, soft-score formula matches upstream's argmax*max_prob/total).
Includes docs/contributing/eval-metrics.md as the porting guide.
Out of scope (deferred follow-ups): MIND, VBench-2.0, FVD as a
registered metric, training-time EvalCallback.
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