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VMAFx documentation

VMAFx measures perceptual video quality: it scores how a distorted video compares with its reference, the way a viewer would judge it. It is a fork of Netflix's VMAF that keeps Netflix's reference scores, adds CUDA, SYCL, HIP and Metal GPU backends and SIMD paths, and holds every GPU result to the CPU's.

Get VMAFx{ .md-button .md-button--primary } Score your first pair{ .md-button }

First score

build/tools/vmaf \
  --reference testdata/ref_576x324_48f.yuv \
  --distorted testdata/dis_576x324_48f.yuv \
  --width 576 --height 324 --pixel_format 420 --bitdepth 8 \
  --json --output scores.json

Start here

1. Get VMAFx: a container image, a release download or a source build.
2. Score your first pair and read the output.
3. Choose a backend for your hardware.
4. Use it through the CLI, the C API or the FFmpeg filter.
5. Look things up in the reference below, or contribute.

Found a problem? Open an issue. Have hardware the project does not own? Run the tester image and send the report.

Backends

• Backend guide

  Choose and build

• x86 SIMD

  AVX2 · AVX-512

• ARM SIMD

  NEON · SVE2

• CUDA

  NVIDIA GPUs

• SYCL / oneAPI

  Intel GPUs

• HIP / ROCm

  AMD GPUs

• Metal

  Apple Silicon

• Exact GPU twins

  Scores equal to the CPU's

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Source: the fragments in `scripts/ci/exact_twins.d/` and `LIBM_TWINS` in `scripts/ci/cross_backend_calibration.py`. An exact twin returns the CPU extractor's bits (=) and is compared with tolerance 0; a libm-bound twin differs only through the math library, within the stated bound (≤); a dash means no twin of that backend is declared either way.

Data table

Feature	CUDA	SYCL	HIP	Metal
adm	exact	exact	exact	not declared
cambi	exact	exact	exact	not declared
ciede	libm bound (≤ 1e-09)	libm bound (≤ 1e-09)	libm bound (≤ 1e-09)	not declared
float_adm	exact	exact	exact	exact
float_moment	exact	exact	exact	exact
float_motion	exact	exact	exact	exact
float_ms_ssim	exact	exact	exact	exact
float_ms_ssim_chroma	exact	exact	exact	exact
float_ms_ssim_lcs	exact	exact	exact	exact
float_psnr	exact	exact	exact	exact
float_ssim	exact	exact	exact	exact
float_ssim_lcs	exact	exact	exact	exact
float_vif	exact	exact	exact	exact
motion	exact	exact	exact	exact
motion_debug	exact	exact	exact	exact
motion_mffw	exact	exact	exact	exact
motion_v2	exact	exact	exact	exact
motion_v2_mffw	exact	exact	exact	exact
psnr	exact	exact	exact	exact
psnr_hvs	exact	exact	exact	not declared
speed_chroma	exact	exact	exact	not declared
speed_temporal	exact	exact	exact	not declared
ssim	exact	exact	exact	exact
ssimulacra2	exact	exact	exact	exact
vif	exact	exact	exact	not declared

Use VMAFx

Topic	Pages
Install and build	Getting started, Building on Windows, Docker
Command line	CLI reference, --precision, environment variables, vmaf_bench
Integrations	FFmpeg, Python library, MATLAB, external resources
Encoding workflows	vmaf-tune (fast path, bitrate ladder, codec adapters, recommend, saliency-aware, resolution-aware, HDR and sampling, cache, bisect), per-shot scoring, ROI scoring, BD-rate utilities
Testing on your hardware	hardware we need, tester image and macOS bundle, build-from-source tester guide, hardware reports

Reference

Topic	Pages
Metrics	Feature reference: every extractor, its options and its GPU twins; CAMBI, SSIMULACRA 2, DISTS, confidence interval, bad cases, AOM CTC (AOM), NFLX CTC
Models	Overview, VMAF v1, datasets
Backends	Backend guide, x86 SIMD, ARM SIMD, CUDA, SYCL / oneAPI, HIP / ROCm, Metal
C API	API overview: contexts, pictures, models, features; GPU, DNN sessions, embedded MCP
MCP servers	Overview, tool reference, embedded server, release channel
Tiny AI	Tiny-AI docs, training, training data, MOS corpora, inference, LOSO evaluation, predictor, conformal VQA, ensemble training kit, ensemble v2 runbook, quantization, quant epsilon, model registry, roadmap
Other	FAQ, references, papers, presentations, benchmarks

Project

Topic	Pages
Plan and releases	Roadmap and release candidates, release process
Contributing	Engineering principles, build flags, IDE setup, CI, CI runners, fuzzing
Correctness	Cross-backend gate, upstream parity guard, Python process execution
Upstream	Upstream watchers, FFmpeg patch refresh
Architecture	Repository layout, Python-harness workspace, ADR log
Security	Repository security, OpenSSF Scorecard, Scorecard and CodeQL audit, 2026-09-04