Bug: positioned-video clips contribute ~0s to output duration (regression of #62 / #123) #231

Found while restoring test fixtures in #230. Both #62 and #123 are closed, but their regression tests never actually ran — they died on a missing gitignored fixture long before reaching their assertions, so the regression went unnoticed.

Evidence

Two compositions, identical except for the middle clip's layers (local backend, ffmpeg 7.x):

const wrap = (mid) => [
  { duration: 2, layers: [{ type: "fill-color", color: "#ff0000" }] },
  mid,
  { duration: 2, layers: [{ type: "fill-color", color: "#0000ff" }] },
];

// middle = fill-color            -> 5s  ✅ (6s minus 2x default 0.5s transition)
// middle = fill + 2 positioned   -> 4s  ❌ (positioned clip contributes ~0s)

Reproduced without any transitions too: 3 clips x 2s = 4s instead of 6s when the middle clip holds positioned videos.

A clip whose only layer is a positioned video still throws:

Clip 0 produced no video output — ensure it has at least one visual layer (video, image, or fill-color)

That is precisely the #123 symptom. It occurs whether or not a fill-color base layer is present, so it is broader than the "no base layer" case #123 described.

Impact

<Split> / <Slot> / Grid layouts inside a <Clip> silently lose their clip's duration, shortening the final video. This is the exact user-facing symptom of #62.

Current state

The two regression tests are marked test.failing in src/ai-sdk/providers/editly/editly.test.ts (PR #230), so they:

• keep the correct expectation encoded in the assertion, and
• fail loudly the moment the bug is fixed, forcing the marker's removal.

They are NOT skipped, and this is NOT fixed in #230 — that PR is scoped to the opentype.js crash and fixture restoration.

Suggested starting point

buildBaseClipFilter / the positioned-overlay path in src/ai-sdk/providers/editly/index.ts — the same code #123 touched. Likely the clip's base segment is emitted with zero duration when all its layers are classified as overlays.

Repro

bun test src/ai-sdk/providers/editly/editly.test.ts -t "issue #62: positioned videos"
bun test src/ai-sdk/providers/editly/editly.test.ts -t "issue #123: clip with only positioned"

(Remove .failing to see them fail.)