The clip is the wrong length or freezes at the end

A limb stops dead a fraction of a second before the rest of the body, or a clip that should be one second long plays a frame short in the engine.

Checks: duration-sanity · fps

Why it happens

A clip's duration is not one number in the file: it is whatever its longest channel reaches, and an engine clamp-holds every channel that ends earlier. A partial export, a slice that dropped one bone's tail keys, or a retiming step that drifted off the frame grid all leave a file that looks valid and plays wrong. The length a clip is supposed to be is project knowledge, so AnimSmith checks the mechanical part always and the declared part only once you pin it.

What AnimSmith measures

The synthetic walk below has one left-ankle rotation channel that stops at 0.75 s while both translation channels run to 1.0 s. The report's judged frame is the moment the short channel starts being held.

Open the interactive report to scrub the frames after the ankle stops.

What the finding looks like

The spread is mechanical, so no configuration is needed to see it:

$ animsmith lint examples/assets/walk-short-channel.glb
examples/assets/walk-short-channel.glb:
  warning[duration-sanity] clip 'walk_short_channel': channels end at different times (0.750s..1.000s) — shorter channels will be clamp-held (measured 0.2500, expected 0.0000)
  coverage[bind-pose] insufficient_rotation_evidence ×1 (scopes: first_frame_rest_delta; subjects: walk_short_channel): only 1 usable first-frame rotation track(s); at least three are required
0 error(s), 1 warning(s), 0 note(s), 1 coverage gap(s), 0 available prediction facet(s), 0 required-unavailable prediction facet(s)   # exits 0

The other half of this symptom — a clip whose channels agree but whose length no longer matches the manifest — has no mechanical signature at all. Only a declared duration_s (and fps for the frame grid) turns it into a finding.

What to do

Channels ending at different times. The export dropped part of a channel. Re-export the full range; duration-sanity reports the spread, it does not resample the clip.
A declared length that is missed. Pin duration_s for the clip and let the check report the measured and expected seconds. The tolerance absorbs harmless exporter rounding, not a wrong authored range.
Keys off the frame grid. Declare fps and fix the retiming step that drifted. Unreal, for example, documents that animations with non-whole end frames do not import correctly.
When the input is deliberately being edited. animsmith transform --slice cuts a window on the frame grid and retimes it to start at zero, and --hold-extend appends a linear hold of the final pose for charge and block poses. See editing a clip.

Who fixes it: the pipeline. A partial export or a drifted retime is repaired where it was produced — a re-export, or an explicit transform when the cut itself is the intended edit. The gate closes when the clip's channels agree, its declared duration and frame grid are met, and the engine plays the whole range.

Config

[clips.walk_short_channel]
# The authored range. Linting reports a missed pin; it never resamples.
duration_s = { value = 1.0, tolerance = 0.02 }
# The grid the clip was authored on, so `fps` can check that its keys stay
# on that grid and that it spans a whole number of frames.
fps = 32.0

Precise contract: channel ends, declared durations, the frame grid, and the mechanical edits

Channels that end at different times mean a partial export. When one bone's track is shorter than the clip, the engine clamp-holds the shorter channel — a limb freezes while the rest of the body keeps moving. The duration-sanity check flags degenerate durations and mismatched channel ends.
A valid-looking clip can still be one frame too short. Export slicing, inclusive-vs-exclusive frame ranges, and endpoint removal can produce a positive duration whose channels agree but which no longer matches the gameplay or animation manifest. Declare duration_s = { value = 1.033, tolerance = 0.02 } for the clip and duration-sanity reports the measured and expected seconds when that pin is missed. The value must be finite and positive, and the tolerance finite and non-negative; invalid pins are errors instead of silently disabling the contract. The tolerance absorbs harmless exporter rounding. Linting only reports the mismatch; it does not repair or resample the clip. Re-export when the authored range is wrong, or use the explicit slice/hold transforms below when the source is intentionally being edited.
Keys off the frame grid mean a retiming step drifted. A clip with a declared frame rate should keep its keys on that rate's time grid and span a whole number of frames. Off-grid keys mean a resample or retiming step drifted; a fractional frame count means a slice cut mid-frame — and engines care: Unreal, for example, documents that animations with non-whole end frames do not import correctly. The fps check verifies both once the config declares a rate.

When the wrong length is the input problem — a capture with garbage at the head, a one-shot that should hold its final pose — the transform command does the mechanical edit: --slice cuts a window on the frame grid and retimes it to start at zero, and --hold-extend appends a linear hold of the final pose (charge and block poses). See editing a clip.

The checks' prerequisites, configuration keys and gap semantics are listed with every other check in the built-in check reference.