Function plan_source_composition 

pub fn plan_source_composition(
    composition: &Composition,
    compositions: &[Composition],
    sources: &[MediaSource],
    canvas: (u32, u32),
) -> Result<CompositionPlan, PlanError>

Compiles composition as a composition source. Like plan_composition, but clip nodes and group inputs are errors because nothing feeds them.

Errors

Returns PlanError as plan_composition does, and for a needed clip node or group input.