- Tracks stack. The first track is the background. Each later track composites on top of the ones below it: overlays, titles, picture-in-picture.
- Clips sit in time. A clip can carry a
startand alengthin seconds, and it can leave both out. Two clips on the same track are joined by a transition. A gap between them plays nothing.
Timing is optional
Every clip sits in a container: the scene it belongs to, or the whole video. Two sentences cover every case.- Omit
lengthand the clip runs as long as its content does, never past its container. - Write
length: "end"and it runs to the end of its container, whatever its content says.
speed (so speed: 0.5 on a 4 second clip occupies 8 seconds), or a composition’s own end.
Text and images have no duration of their own, so for them the two sentences say the same thing. A title with no length stays up for the whole video, which is what a watermark wants.
start follows the same shape: omit it and the clip begins after everything already placed on its track, pulled back by any transition immediately before it. Give it a number and that is seconds from the start of its container.
Set either field wherever you want something else. Every timeline written with full timing keeps rendering exactly as it did.
Worked examples
A music bed. The source is three minutes long, the video is not, and"end" is how you say so without totalling the clips above it.
start. The music names length: "end", so it stops on the last frame whatever the video adds up to.
The rules that fall out of it
A clip running to the end of the video is measured against every clip that is not, so two of them on different tracks both land on the real end rather than chasing each other. It runs to the last frame, so nothing may follow it on the same track, and a timeline where nothing has a length of its own has no end to measure and is rejected. A clip never runs past its container, so a 6 second video in a 3 second scene plays 3 seconds, and a 2 second video in a 5 second scene plays 2. That applies to a length you wrote as well as one the engine worked out."end" is the opposite request and does not cap: it asks for the container’s full extent whatever the source holds. On a source shorter than the container that is impossible, and the job is rejected for outrunning its source. Leave the length off instead, or trim less.
Inside a composition, start and length both stay required. A nested timeline’s length is set by the clip hosting it, so there is nothing to append to and no container to measure against.
Add a layer
A second track renders over the first. This lays an animated title over the video.before
background #059669
Scene-first authoring
Tracks give you precise multi-track control. For a sequential edit, you can instead describe a list of scenes. Each scene is a self-contained segment with its own clips. A scene’stransition blends INTO it from the previous scene, so put it on the second of two scenes. overlays is a flat list of clips that sit over the whole composition, like a persistent logo or watermark.
start and length to span the whole scene, and a scene can omit its own duration to take the length of the video inside it. Every clip field works the same as in tracks mode. scenes and tracks are mutually exclusive: a timeline uses one or the other.
two scenes, crossfaded
before
a logo over both scenes
A timeline as one clip
Acomposition asset holds a whole timeline of its own, so a group of layers can be moved, scaled and faded together rather than one at a time.
before
scaled and tilted as one clip