TAD — Temporal Absolute Difference¶

Feature name (CLI): tad Output scores: tad, tad_sad Implementation: Rust (cbindgen pilot — ADR-0707) Availability: CPU only. Requires enable_rust_features=true (default when cargo is in PATH).

What it measures¶

TAD is the mean absolute difference of luma (Y) pixel values between a reference frame and a distorted frame, normalised to the [0.0, 1.0] range by the peak luma value (2^bpc − 1):

tad(ref, dis) = (1 / (W × H × peak)) × Σ_{i,j} |ref_Y[i,j] − dis_Y[i,j]|

where:

W × H = number of luma pixels per frame
peak = maximum luma sample value (255 for 8-bit, 1023 for 10-bit, etc.)
Only the luma (Y) plane is used; chroma planes are ignored.

A second sub-score tad_sad reports the raw (unnormalised) sum of absolute differences, useful for debugging without the normalisation step.

Score range and interpretation¶

TAD value	Meaning
0.0	Reference and distorted frames are pixel-identical.
0.0 – 0.05	Very small per-pixel error; typically high-quality encoding.
0.05 – 0.2	Moderate per-pixel error; perceptual quality may still be good depending on spatial distribution.
0.2 – 1.0	Large per-pixel error; indicates significant distortion.
1.0	Maximum possible mean error (every pixel at the opposite extreme).

Important: TAD measures raw pixel fidelity, not perceptual quality. A low TAD score is a necessary but not sufficient condition for high perceptual quality. Spatially structured errors (blocking, ringing, blur) can produce low mean errors while being visually objectionable. Use TAD as a lightweight pre-filter or diagnostic tool, not as a substitute for VMAF.

Usage¶

# Score a single reference/distorted pair and include TAD:
vmaf --reference ref.yuv --distorted dist.yuv \
     --width 1920 --height 1080 --pixel_format yuv420p --bitdepth 8 \
     --feature tad

# TAD alongside the default VMAF model:
vmaf --reference ref.yuv --distorted dist.yuv \
     --width 1920 --height 1080 --pixel_format yuv420p --bitdepth 8 \
     --model version=vmaf_v0.6.1 --feature tad

The output JSON will contain per-frame tad and tad_sad scores, and their aggregate (mean, harmonic mean, etc.) in the summary block.

Build requirements¶

TAD is implemented in Rust. The Meson build option enable_rust_features (default true) controls whether the Rust crate is compiled. When cargo is not found at configure time, the option is automatically set to false and the TAD extractor is silently omitted.

# Explicit opt-in (default):
meson setup build -Denable_rust_features=true

# Opt-out (e.g. on hosts without a Rust toolchain):
meson setup build -Denable_rust_features=false

When enable_rust_features=false, requesting --feature tad at runtime returns -ENOSYS (feature not available).

Caveats and limitations¶

Luma only. The metric intentionally ignores chroma, matching the convention of most VMAF component features which also focus on the luma plane. A future tad_chroma variant could be added.
No temporal context. TAD is computed independently per frame pair; it does not accumulate across frames and has no temporal memory.
Not part of any VMAF model. TAD scores do not affect VMAF scores; it is an additive signal only.

Implementation notes¶

Source files:

core/src/feature/rust/tad/src/lib.rs — Rust implementation + unit tests
core/src/feature/rust/tad/Cargo.toml — crate manifest (cbindgen build-dep)
core/src/feature/rust/tad/build.rs — cbindgen header generation
core/src/feature/tad_rust.c — C wrapper adapting the Rust ABI to VmafFeatureExtractor

Architecture: ADR-0707 documents the cbindgen → Meson integration recipe. Future Rust feature extractors should follow the same pattern.