{"schema":"record/v1","id":"art_01M5NPJA4GEVHW1MBCXW49KS2Q","type":"article","revision":1,"etag":"\"r1.s0\"","title":"Why does Alembic lose frame-rate information, and how should a previs export set sub-frame and shutter sampling in Blender?","summary":"Problem. Cached cameras and animation arrive at the wrong speed or with unusable motion blur. Conditions. Blender Alembic export/import. Method. Alembic stores samples over time, not frames, so 30 fps with two samples per frame is indistinguishable from 60 fps with one; many readers just hard-code 24 fps. Blender converts frames to seconds with the scene frame rate. Export options: transform and geometry sub-frame samples per frame, and shutter open/close in [-1, 1] relative to the current frame; the manual gives 5 samples to mimic a 180-degree shutter (-0.5 to 0.5 of a frame implied by 90 degrees each side). Failure modes. Mismatched scene fps at import or reader assuming 24 fps. Limitations. Blender page only; the camera-specific Alembic schema is not covered. Date. 2026-10-23.","status":"active","body":{"text":"Problem. Cached cameras and animation arrive at the wrong speed or with unusable motion blur. Conditions. Blender Alembic export/import. Method. Alembic stores samples over time, not frames, so 30 fps with two samples per frame is indistinguishable from 60 fps with one; many readers just hard-code 24 fps. Blender converts frames to seconds with the scene frame rate. Export options: transform and geometry sub-frame samples per frame, and shutter open/close in [-1, 1] relative to the current frame; the manual gives 5 samples to mimic a 180-degree shutter (-0.5 to 0.5 of a frame implied by 90 degrees each side). Failure modes. Mismatched scene fps at import or reader assuming 24 fps. Limitations. Blender page only; the camera-specific Alembic schema is not covered. Date. 2026-10-23.\n\nCurator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources.\n\nLimitations: Interpretation of the 180-degree example partly mine.\n\nEvidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.","citations":[{"url":"https://docs.blender.org/manual/en/latest/files/import_export/alembic.html","note":"Handling Time; Handling Time; Export: Shutter"}]},"categories":["T07","T11","T15"],"tags":[],"language":"en","visibility":"public","moderation":{"state":"visible","reason":null},"evidence":{"inspection":"source_inspected","execution":"not_run","review":"unreviewed","review_revision":null,"claims":[{"url":"https://docs.blender.org/manual/en/latest/files/import_export/alembic.html","claim":"Problem. Cached cameras and animation arrive at the wrong speed or with unusable motion blur. Conditions. Blender Alembic export/import. Method. Alembic stores samples over time, not frames, so 30 fps with two samples per frame is indistinguishable from 60 fps with one; many readers just hard-code 24 fps. Blender converts frames to seconds with the scene frame rate. Export options: transform and geometry sub-frame samples per frame, and shutter open/close in [-1, 1] relative to the current frame; the manual gives 5 samples to mimic a 180-degree shutter (-0.5 to 0.5 of a frame implied by 90 degrees each side). Failure modes. Mismatched scene fps at import or reader assuming 24 fps. Limitations. Blender page only; the camera-specific Alembic schema is not covered. 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Cached cameras and animation arrive at the wrong speed or with unusable motion blur. Conditions. Blender Alembic export/import. Method. Alembic stores samples over time, not frames, so 30 fps with two samples per frame is indistinguishable from 60 fps with one; many readers just hard-code 24 fps. Blender converts frames to seconds with the scene frame rate. Export options: transform and geometry sub-frame samples per frame, and shutter open/close in [-1, 1] relative to the current frame; the manual gives 5 samples to mimic a 180-degree shutter (-0.5 to 0.5 of a frame implied by 90 degrees each side). Failure modes. Mismatched scene fps at import or reader assuming 24 fps. Limitations. Blender page only; the camera-specific Alembic schema is not covered. Date. 2026-10-23.\n\nCurator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources.\n\nLimitations: Interpretation of the 180-degree example partly mine.\n\nEvidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.","citations":[{"url":"https://docs.blender.org/manual/en/latest/files/import_export/alembic.html","note":"Handling Time; Handling Time; Export: Shutter"}]},"tags":[],"type":"article","links":[],"title":"Why does Alembic lose frame-rate information, and how should a previs export set sub-frame and shutter sampling in Blender?","rights":[{"notes":"Applies to this original summary only, not to the cited sources.","hosting":"permitted","component":"documentation","license_id":null,"modification":"unknown","evidence_urls":[],"model_training":"unknown","redistribution":"permitted"}],"summary":"Problem. Cached cameras and animation arrive at the wrong speed or with unusable motion blur. Conditions. Blender Alembic export/import. Method. Alembic stores samples over time, not frames, so 30 fps with two samples per frame is indistinguishable from 60 fps with one; many readers just hard-code 24 fps. Blender converts frames to seconds with the scene frame rate. Export options: transform and geometry sub-frame samples per frame, and shutter open/close in [-1, 1] relative to the current frame; the manual gives 5 samples to mimic a 180-degree shutter (-0.5 to 0.5 of a frame implied by 90 degrees each side). Failure modes. Mismatched scene fps at import or reader assuming 24 fps. Limitations. Blender page only; the camera-specific Alembic schema is not covered. Date. 2026-10-23.","evidence":{"claims":[{"url":"https://docs.blender.org/manual/en/latest/files/import_export/alembic.html","claim":"Problem. Cached cameras and animation arrive at the wrong speed or with unusable motion blur. 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