VMAF measurement-and-pooling script

A dependency-light Python script (standard library only) that runs VMAF on a (reference, distorted) pair with FFmpeg's libvmaf filter, then parses the per-frame JSON log and reports the score pooled four ways — mean, harmonic mean, 5th percentile, and the single worst frame — so you can see how much the headline mean hides. It prints the model used (so numbers are reproducible) and reads any gap against Netflix's ~6-point just-noticeable-difference rule of thumb. Includes the current FFmpeg/libv