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@github-actions github-actions released this 23 May 19:48
· 57 commits to main since this release
v1.3.1
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Changelog

All notable changes to this project are documented here. Format loosely
follows Keep a Changelog, versioning is
SemVer.

[1.3.1] — 2026-05-23

Patch release. Performance-only — pixel output unchanged from 1.3.0
on every supported parameter combination.

Changes

  • SIMD coverage extended to the three output-stage functions in
    src/output.zig:
    • simpleBlur (diMode=2): 32-lane motion-hit count + 16-lane luma
      body with overlap-loaded 3-tap motion neighbours.
    • deintOneField (diMode=3, default): 16-lane luma body using
      cross-row field-map OR-mask + pavgb + @select; chroma
      unconditional via tight LANES/2 pass.
    • deinterlace (diMode=1): 32-lane luma with all five IV scores +
      @select-chain min-pick + motion override.
  • ARM64 binaries included by default (Linux aarch64 + macOS
    aarch64) since the 1.3.0 release-workflow rework.

Speed delta vs 1.3.0 (720x480 NTSC, ReleaseFast, best-of-3)

Pipeline 1.3.0 1.3.1 Δ
fps=30 3217 fps 3175 fps ~0 (noise)
fps=24 3148 fps 3023 fps ~0
fps=24 diMode=1 3041 fps 3215 fps +5.7%
fps=24 blend=1 2353 fps 2301 fps ~0

The default fps=24/fps=30 paths don't move measurably because most
frames on telecined NTSC content classify as ip='P' and skip the
deinterlacer entirely. Workloads that hit ip='I' frequently
(interlaced-heavy content, or pthreshold=1-forced runs) see the
diMode=1 gain on every frame.

Bit-exactness

Default-path 720-frame regression against the API-4 upstream port
still passes byte-for-byte. diMode=1 SIMD was independently
verified against the pre-SIMD scalar build (80 frames, all md5s
identical).

[1.3.0] — 2026-05-23

Initial release. A from-scratch Zig port of the VapourSynth-IT
inverse-telecine filter, bit-exact to the upstream C reference path
and with the original Avisynth-only parameters restored.

Version numbering picks up the IT lineage:

  • Avisynth IT_YV12 v0.1.03 (minamina, 2003)
  • VapourSynth VS_IT.dll v0103.1.2 (msg7086, 2014)
  • This Zig port: v1.3.0.

Features

  • Filter core.zit.IT(clip, fps=24, threshold=20, pthreshold=75, ref="TOP", blend=0, diMode=3) registered for VapourSynth API 4
    (R55+). Accepts YUV420P8 input with width % 16 == 0, height % 2 == 0,
    width ≤ 8192.
  • Decimation modes:
    • fps=24 — 3:2-pulldown removal, output 24000/1001 fps (5→4
      frames per cycle).
    • fps=30 — field-matching only, input rate preserved.
  • ref parameter ("TOP"/"BOTTOM"/"ALL"/"NONE"): the
    Avisynth original's field-match-direction switch, fully reimplemented.
    The VapourSynth upstream had stripped this down to a hardcoded
    "TOP".
  • blend parameter: pure-Zig port of Avisynth's BlendFrame_YV12,
    triangular kernel weighted blend of post-matched frames, motion-gated
    on the same minD/avgD heuristic as the original. Only active when
    fps=24.
  • diMode parameter with all four Avisynth deinterlace modes:
    • 0 DI_MODE_NONE — straight field copy, no deinterlace.
    • 1 DI_MODE_DEINTERLACE — full per-pixel five-candidate scorer
      with motion-gated vertical-average fallback (~500 LoC of Avisynth
      MMX re-expressed as pure scalar Zig).
    • 2 DI_MODE_SIMPLE_BLUR — vertical (T+2C+B)/4 blur on
      motion-flagged pixels.
    • 3 DI_MODE_ONE_FIELD — default; field-interpolation using the
      simple-blur and motion2max maps.

Frame properties

  • Standard, always set on output: _FieldBased=0, _Combed per
    frame, _DurationNum/_DurationDen derived from output rate. All
    source props (_Matrix, _Transfer, _Primaries,
    _ChromaLocation, _SARNum/Den, _Range/_ColorRange, …)
    inherited via propSrc in newVideoFrame.
  • Diagnostic (per-frame inspection for power-user scripts):
    ITMatch, ITMflag, ITIpFlag (utf8 1-char each); ITIvC/P/N/M,
    ITDiffP0/P1/S0/S1, ITBlended (ints).

Verification

  • Bit-exact to a mechanically API-3 → API-4-ported build of the
    upstream C reference (reference/vapoursynth-cpp-api4/). 198 frames
    across 10 fixture × parameter combinations, plus 720 frames of two
    real telecined NTSC VOB samples in both fps=24 and fps=30 mode,
    byte-for-byte identical.
  • 35 Zig unit tests for the algorithm primitives + SIMD helpers.
  • 58 Python/VapourSynth integration tests — invariants,
    property checks, error paths, the regression-pinned md5 hashes, the
    upstream-compare matrix, and the new parameter sweeps.

Performance

500 frames of 720×480 NTSC, ReleaseFast build, single-threaded
fmParallelRequests:

Pipeline fps
core.zit.IT(clip, fps=30) ~2700
core.zit.IT(clip, fps=24) ~2200
core.zit.IT(clip, fps=24, diMode=1) ~2350
core.zit.IT(clip, fps=24, blend=1) ~1700
core.vivtc.VFM(clip) (reference) ~600
core.vivtc.VFM + VDecimate (ref) ~1270

~4× faster than vivtc.VFM at field-matching, ~2× faster than
vivtc.VFM + VDecimate at IVTC, using the pure-C path + portable
Zig @Vector(N, u8) SIMD (pavgb, psubusb, pmaxub/pminub
equivalents).

Differences from the VapourSynth upstream

The upstream
VapourSynth-IT
plugin (msg7086, 2014) was a partial port of the Avisynth original.
This port reintroduces what was stripped and fixes four framework-level
issues:

  1. ref, blend, diMode=0/1/2 reinstated (upstream hardcoded
    ref="TOP", blend=false, diMode=3).
  2. Frame properties: upstream passes propSrc=null to
    newVideoFrame, so output frames carry no metadata at all. We
    inherit source props and set _FieldBased/_Combed/_Duration*
    explicitly.
  3. Threading mode: fmParallelRequests. Upstream registered as
    fmParallel despite sharing mutable per-instance state — a latent
    race condition the modern VS scheduler hits more often.
  4. Frame-request range widened to [base-2, base+6] (fps=24) /
    [n-2, n+2] (fps=30) so all reads through getFrameFilter are
    satisfiable. Upstream relied on API 3's sync getFrame to pull
    neighbours from cache; under API 4 that is not allowed inside a
    filter callback.
  5. Edge clamping: getFrameFilter(n, …) is called with n clipped
    to [0, numFrames-1]. Under API 3 the core silently clamped; under
    API 4 it returns null and a deref crashes.

Build & packaging

  • zig build --release=fast produces zig-out/lib/libzit.so on the
    host platform.
  • zig build cross produces release binaries for all three targets
    under zig-out/{linux,macos,windows}/:
    • libzit-linux-x86_64.so
    • libzit-macos-x86_64.dylib
    • zit-windows-x86_64.dll
  • GitHub Actions workflow under .github/workflows/ci.yml runs
    lint + unit + cross-build + integration on workflow_dispatch only;
    push/pull-request triggers can be enabled by appending to the on:
    block.

Credits

Algorithm: thejam79 (IT 0.051, 2002), minamina (IT_YV12 0.1.03, 2003),
poodle (64-bit / 8k mod), msg7086 (VapourSynth port, 2014). Zig port:
this repo.

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