Transitions

What it does

A transition is a property of one join, not of the whole video. Each cut between two scenes carries its own — a dissolve here, a straight cut there — so a piece can open soft and stay tight.

The library is everything ffmpeg’s xfade can do. A brand keeps four or five to hand; the rest stay in a vault you open when you want them, so the control is a choice rather than a list of fifty-eight.

The standard behind it

• A transition is clamped against the shorter of the two scenes it joins. A half-second dissolve across a third-of-a-second beat would consume that beat whole, so the renderer shortens the transition rather than eating the shot.
• Three seconds is the ceiling. Past that it is not a transition, it is a scene.
• The outgoing scene is lengthened by the transition’s own duration before the fade is applied. Without that it has nothing left to fade from, and ffmpeg does not shorten gracefully — it mangles the output rather than trimming it.
• A straight cut never builds a filter graph at all. It takes the concat path, so it costs nothing and re-encodes nothing.