compose_layout: Compose Video Streams onto a Canvas per a Layout

In compost: Video Compositing via 'FFmpeg'

Compose Video Streams onto a Canvas per a Layout

Description

Paints each named source into its slot's pixel rect on a black canvas, in slot order (first = bottom). fit = "fill" covers the rect (scale-up + center-crop, for heads); fit = "fit" contains (scale-down + centered pad, for content). Every chain is normalized (fps, square pixels, yuv420p), non-reference chains freeze their last frame if shorter, and the output is cut frame-exactly to the reference source's length. The output carries no audio.

Usage

compose_layout(sources, output, layout, reference = names(sources)[1],
               overwrite = TRUE, dry_run = FALSE)

Arguments

sources	Named character vector or list of video paths, keyed by slot name; must cover every slot in layout$slots.
output	Path for the output video file.
layout	A cornball layout: list(schema, name, canvas, slots), with slots a named list of list(rect = c(x, y, w, h), fit = "fill"|"fit") in integer pixels (see system.file("schema", "cornball-layout.md", package = "compost")).
reference	Slot name whose source defines the output frame rate and length (default the first source).
overwrite	If TRUE (default), overwrite the output file.
dry_run	If TRUE, return the FFmpeg command without executing.

Value

Invisibly returns the output path. If dry_run, returns the command string.

Examples

## Not run: 
layout <- list(schema = 1L, name = "vertical", canvas = c(1080L, 1920L),
               slots = list(
                   narrator = list(rect = c(0L, 0L, 1080L, 960L),
                                   fit = "fill"),
                   visual = list(rect = c(0L, 960L, 1080L, 960L),
                                 fit = "fit")))
compose_layout(c(narrator = "head.mp4", visual = "slides.mp4"),
               "composed.mp4", layout, reference = "visual")

## End(Not run)

compost documentation built on Aug. 4, 2026, 5:11 p.m.