CityHall 4K — half the size, the eye cannot tell.

Same 10 seconds. Same 4K, 60 fps. The right side is NormH.264 at half the byte count, VMAF 83.83. Both auto-play below — judge for yourself.

Source — AV1 4K60 · 17.94 MB
cityhall_4k_av1_original.webm · already-compressed AV1 from open-web download

NormH.264 — H.264 4K60 · 9.10 MB (−49.27%)
cityhall_4k_norm_h264.mp4 · VMAF 83.83 / VMAF min 76.11 · plays everywhere H.264 plays

17.94 MB → 9.10 MB

Half the byte count. VMAF 83.83. Visually indistinguishable on cityscape detail. Identical playback compatibility.

Notice the playback itself. The 18 MB AV1 source on the left and the 9 MB NormH.264 on the right both fit on broadband, but watch the start latency and any stutters — the smaller file simply plays earlier and smoother. Compression delta = delivery and UX delta.

Why this is hard

The source is not a fresh H.264 master — it is already AV1, already squeezed by AOM's reference encoder. Most "save 50%" demos start from a high-bitrate master where there is plenty of slack to give back. Here, the slack is already gone, and NormMAP still halves the file while staying inside the visually-identical band.

Spec

Source	CityHall_3840x2160.webm (open-web AV1 download)
Resolution	3840 × 2160 (4K UHD), 60 fps, 10.0 s
Source codec	AV1 (yuv420p), bitrate ~15.7 Mbps
Output codec	H.264 (yuv420p), via NormH.264 v0.3.2
NormMAP config	commutator-norm block-level bit allocation, libx264 ROI side-data path
VMAF mean	83.83 (visually-identical band: VMAF 80–90)
VMAF min	76.11 (worst-frame floor)
Size delta	−49.27% versus 4K AV1 source
Decode compatibility	H.264 — every browser, every device, every set-top, including Safari iOS without polyfills

Want to run this yourself? Get the 30-day trial of SlimeCodec NormH.264 →