cornball-layout.md
In compost: Video Compositing via 'FFmpeg'

The cornball layout contract

compost's render_timeline() can compose several video tracks onto one canvas — a talking-head over slides, a stacked short, an over-shoulder box — driven entirely by data on the OTIO timeline. Writers (any tool emitting OTIO via rotio) declare WHERE things go; compost executes the rects generically and knows no layout names.

Timeline metadata:

metadata(timeline)$cornball$layout <- list(
    schema = 1L,
    name   = "vertical",                 # informational label
    canvas = c(1080L, 1920L),            # output size, even pixels
    slots  = list(                       # list order = paint order (first = bottom)
        narrator = list(rect = c(0L, 0L, 1080L, 960L),   fit = "fill"),
        visual   = list(rect = c(0L, 960L, 1080L, 960L), fit = "fit")))

rect = c(x, y, w, h) in integer pixels of the canvas; w/h even.
fit = "fill" covers the rect (scale up + center-crop — heads); fit = "fit" contains (scale down + centered black pad — content).
The slot named visual binds to the timeline's content track (the first non-caption, non-roled video track), assembled exactly like a single-stream render (source ranges, transitions, still/sequence pre-render, motion effects), and is the timing reference: the composed output has its frame rate and length.
Every other slot name binds to a Video track carrying metadata$cornball$role == "<slot name>". Slot tracks are assembled the same way, normalized (fps, SAR, yuv420p), and muted by construction: the compose emits video only, and the final render maps the timeline's audio-bed track — a layout can never hijack the narration.
A slot source shorter than the reference freezes its last frame; longer is cut. Any number of slots is allowed (b-roll, screencap, logo — just more roled tracks with rects).

Mirrors the cornball.* effects namespace: a renderer that cannot honor the layout still renders the content.

| condition | behavior | |---|---| | schema > supported | one warning, layout ignored, single-stream render | | layout slot with no matching track | one warning, composition skipped | | roled track with no layout slot | one warning, track ignored | | older compost (pre-layout) | roled tracks silently dropped; framing applies — a correct letterboxed single-stream render |

cornball-effects.md — the cornball.* per-clip effect namespace (Ken Burns motion on still clips).