Understand tracks, clips, intervals, visual evidence, and frame-accurate editing.
The timeline is the temporal model of the composition. Every layer occupies a half-open frame interval: it begins at a start frame, remains active for its duration, and stops before its exclusive end frame.
The timeline converts between three related domains:
Composition frame — the global project position.
Layer-local frame — composition frame minus the layer’s start.
Source time — the media sample selected after trim offsets and playback-rate mapping.
When a video is trimmed from the left, its composition start can move while the first visible source sample also advances. Moving the whole clip changes composition placement but should preserve its chosen source range.
Rows encode both temporal intervals and visual stack relationships. A clip can overlap another in time yet remain invisible because it is below an opaque layer. A container row can also own child layers whose geometry and timing are resolved in the parent’s context.
Read the timeline vertically to understand compositing and horizontally to understand time. Most difficult editing issues require checking both axes.
