37 lines
2.1 KiB
Markdown
37 lines
2.1 KiB
Markdown
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# Time selection
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Project `:fps` is the playback and export grid. Each symbol has its own native
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`:fps` and `:frames`; keys, spans, trace choices and corrections stay in that
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native space. A symbol without an explicit rate inherits the document rate;
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changing project fps first records that rate so its existing timing stays put.
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An output frame selects the latest native frame at or before its time:
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`floor(output-frame * native-fps / output-fps)`. Thus 30fps content in a 12fps
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project reads source frames 0, 2, 5, 7, 10… and retains its duration. A partial
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last output frame is included. Changing back to 30 restores the original grid.
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Nothing rewrites or discards the dense measurements.
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The same boundary selection runs when entering a placed symbol. Placement and
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artistic speed are applied before selection; the stored `:time :rate` and
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`:playback :speed` never contain a frame-rate conversion. The derived maps used
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by timeline rows, picking and editing account for the units of each symbol.
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`clip/frames` is a native length; `clip/output-frames` is a transport/export
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length. Resolver frame queries return native frames for edits.
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There is one fps control. The old transient picture-fps control and node
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sample-fps fields are gone. Existing exposure, trace choices and per-instance
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pose tracks remain available: a pose track can hold a chosen closed-mouth frame
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without deleting its neighboring measurements. Those choices stay in native
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frames when output fps changes. Automatic content-aware frame selection is not
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implemented. An event between output frames appears on the next output frame;
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it cannot create an extra frame in a 12fps output.
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Audio uses continuous time through the same derived placement maps, without
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picture floors or holds. Frame-rate units cancel before Web Audio playbackRate
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is set, so only deliberate speed changes affect pitch and duration. Export and
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playback use the same output count and resolver.
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Earlier imports with frame-rate conversion baked into stored retimes must be
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re-imported. There is no second reader for that representation. Source video
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presentation timestamps are still future work; this model assumes constant fps.
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