Placeholders & blocking
A placeholder is a scene object with no media file behind it yet. It lets you author the whole chapter before a single frame is shot: where the panel hangs, how big it is, how long the shot runs, what the viewer must look at to advance.
Why block?
Real productions rarely have the footage first. With placeholders you build the story now: a grey stand-in occupies the exact space and time the finished media will, so you can position it, animate it, put a gate on it and walk the whole chapter on a timeline that already has its final shape. When the shoot wraps, you drop the real file onto the stand-in and keep everything you authored.
Three kinds of placeholder
| Placeholder | Stands in for | You set |
|---|---|---|
| Video Panel | A video file played on a panel | Panel width and height, intended length |
| Immersive Video | A 180° or 360° video | Projection, intended length |
| 3D Entity | A USDZ model | Bounding box width, height and depth |
The intended length is a planning note for the shoot, not an enforced limit. Nothing checks the finished footage against it, so treat it as the brief you're writing for future you.
Creating one
Add it like any other object. Placeholders live in the same Add menu as real entities, in the toolbar and in the Insert menu. For an immersive shot, use the segment inspector's backdrop picker instead, which gives the plate a start time and duration on the timeline.
Name the shot. The name you give it is what floats on the grey proxy in the viewer and labels its clip on the timeline. A placeholder has no filename, so the name is how everyone knows what goes there.
Size and time it. Set the panel size or bounding box, and the intended length for time-based shots. The proxy renders at the authored size, so a three-meter panel occupies three meters of your composition right now.
Author on top of it. Reveal it, move it, key it, gate it. It behaves like any other object in the scene list, the library and the timeline, where its clip carries a dashed outline icon.
Note. The proxy is deliberately flat, unlit grey. It doesn't read as a failed video (black) or as finished art; it reads as a hole with a name, which is exactly what it is.
Filling one
Drag the real file onto the placeholder from the library, from a scene-list row, onto its clip on the timeline, or straight onto the grey proxy in the viewer. The target shows a dashed accent outline while the file is over it. Or, in the inspector's Placeholder section, use Replace Asset… to pick a file from disk or From Chapter to pick media already imported.
Everything you authored carries over: timing, position, rotation, scale, keyframes, fades, gates and interactions. Because a placeholder can't play, the swap also authors the playback for you, adding a play at the start of each span the stand-in held and a stop at the end. The whole replacement is one undo step.
Tip. Type rules are enforced: a video only lands on a Video Panel or Immersive placeholder, and a USDZ only on a 3D Entity. A wrong drop is refused with a message naming the file, so nothing silently becomes the wrong kind of thing.
Reverting one
Content and placeholder are two states of the same object, so the swap has an exact inverse: Revert to Placeholder, in the scene list's context menu and the inspector's Placeholder section. Same transform, same animation, same gates; only the auto-authored play and stop pair is removed. The intended length is re-seeded from how long the clip actually ran, and the media file stays in your library. Reverting reopens the slot; it never deletes footage.
Placeholders never reach your audience
Blocking is an authoring concept. In the finished experience a placeholder deliberately renders nothing: an unfinished shot simply doesn't appear, and actions that target it do nothing. A grey box shipping to an audience would be indistinguishable from a bug, so the player refuses to show one.
Note. Placeholders sync to a connected Vision Pro like any other edit, so your blocking is visible in the headset session. Creating and filling them is done in Chapter Studio on the Mac.
Details worth knowing
- Names are identity. Placeholder names must be unique; duplicates get a number appended, and renaming rewrites every reference in the document.
- Changing the role resets size and projection to sensible defaults for the new kind. Your name and production notes always survive.
- Deleting is two different things. Deleting the clip on the timeline removes that use; deleting the object in the scene list removes it everywhere, and the confirmation tells you how many step gates it also cleared.
- Lights, primitives and text can't revert. They never stood in for an asset, so Revert to Placeholder is refused for them.
Placeholders pair naturally with your first chapter's workflow: block the beats, review the pacing on device, then replace stand-ins as media arrives from the shoot.