Stack ownership and visibility

The learning chapters show the everyday rule: a call with omitted Video or Audio inputs consumes matching values produced nearby. This page explains what happens when bodies and nested compositions create more than one stack frame.

Values and occurrences are different

A Video or Audio value is an immutable graph result. A statement places an occurrence of that value on a stack. A program consumes occurrences and returns new values.

Referencing a name creates another usable occurrence without copying or moving the underlying graph:

image("title.png", 1s) as title
$title
$title
concat

concat can consume both references. The original named value continues to identify the same immutable result.

Bodies create ownership boundaries

Each source-program invocation and program body owns the occurrences created directly in its stack frame. Ownership prevents an inner operation from accidentally consuming unrelated values created by a caller or enclosing body.

Most direct built-ins and imported programs use owned access: omitted inputs may come only from the current owned frame. join and during use visible access because their bodies commonly need the values those programs provide.

Explicit access is local

@owned restricts one block or call to the current ownership frame. @visible allows one call to search enclosing visible frames until it reaches an owned boundary:

@owned {
    image("inside.png", 1s)
    @visible concat
}

The owned block stops the visible concat from reaching Videos outside the block. Access annotations apply only to the form that they prefix. They do not change every nested operation.

Use explicit access only when a nested composition genuinely needs different visibility. Ordinary linear compositions should rely on each program’s documented default.

Names do not create lexical graph scope

Stack ownership and name visibility are separate. A graph name created in a nested body remains available throughout the containing source-program invocation. Temporary body-input names such as $before, $after, and $timeline exist only while that body is active.

A bare { ... } stack block groups work. It returns every child-stack value left inside it. The block is not a lexical name scope.

clip { ... } combines one timeline type and removes its temporary outer occurrence. An optional name remains available for later references.

See Stack binding for exact selection rules and Composition forms for clip, stack blocks, names, and references.