Asset audit - check the media before blaming the scene

Most "the mask is broken / content is misaligned / corners aren't rounded" reports are ASSET problems. Audit first; it takes a minute and saves a debugging afternoon.

The checklist

1. Alpha padding (the #1 trap). Sticker-style PNGs bake transparent margins into the canvas: fit: cover covers the box with the FULL canvas, so the visible content sits inset and any rounding or mask lands in the transparent margin - the visible edge is the asset's own square boundary. Check it by looking: build a one-layer scene whose composition is the asset's own size (from picsart_media_probe), background: "#ff00ffff", the asset with fit: "contain", and look at it with picsart_scene_contact_sheet (resolution set to the composition size). No magenta inside the frame: clean. Magenta around the subject: a padded sticker; trim it, or use it deliberately as a decal with no look.
2. Dimensions and aspect: picsart_media_probe (no download; EXIF-corrected width and height, duration for video). Cover-fit crops from decoded dimensions - a 4:3 photo in a 9:16 card loses its sides; check the subject survives the crop. Also compare the asset's size with its largest placement box: scale = max(box_w / own_w, box_h / own_h), and a scale above 1 is an upscale. A 585x1024 photo in a 1080x1920 full-bleed box is stretched to nearly double. Rendering can decode an asset whose dimensions are omitted, but query and selection geometry cannot invent them: for fit: "none", declare both width and height when the layer must be selectable or queryable, or use its intrinsic centre as the default transform anchor. Without them the source still renders at natural size, but picsart_scene_query_layout returns no bounds and the fallback pivot is the content origin. Do not add content.bounds as a workaround: fit: "none" has no destination box and rejects bounds and align. When a scene already declares an asset's width/height, compare them with the probe: a mismatch means the document describes a different file than the one that will load.
3. Video specifics: duration against the trim window you plan (a trim beyond the end freezes the last frame); first frames may decode dark or blank, so don't trim in exactly at 0 or at a scene cut; embedded audio (mute it unless wanted); reversed playback does NOT reverse audio.
4. URL reuse: fine. The same media URL in two different boxes renders correctly. Do NOT add a distinct #fragment per instance: it defeats content dedup, and it silently rewrites a URI that already carries a fragment of its own.
5. SVG data-URIs: encode only < > space; raw spaces in interpolated text are tolerated, raw # is not (colours as hex-without-# interpolated after %23). Declared width and height on the asset matter - undeclared dimensions break mask plus bounds combinations.
6. Content vs box semantics: an asset that is itself a full-bleed photo behaves under any fit; UI screenshots and renders with baked-in margins do not - measure where the content actually starts.

Is the reference element MASKED?

When sourcing assets for a recreation of a reference video, decide for every photographic element whether you are looking at a WHOLE asset or a MASKED VIEW of a larger one. Baking the mask into the bitmap gives the right pixels and the wrong scene: the photo can no longer be swapped, the mask cannot animate, and the "asset" is a screenshot of someone else's render. Narrow slivers cut from the visible part of a card, or a full frame grabbed as a "photo", are this mistake.

How to tell, cheapest test first:

1. Does content continue past the edge across frames? A masked view is a WINDOW: as the card moves, grows, or the mask animates, NEW parts of the same photo appear at the edge while the rest stays registered. Sample the element at 3-4 timestamps in its own span (picsart_media_video_stills) and check whether its content translates WITH the box (a whole asset moving) or STAYS PUT while the box reveals more of it (a mask sliding over a fixed image). The second is a mask, always.
2. Is a feature cut mid-stride? A hard straight edge slicing a face, a hand, or a horizon mid-feature is a mask boundary; a real asset's edge lands where the photographer put it.
3. Does the aspect ratio look impossible? 238x1095 (1:4.6) is not a photograph anyone shot; it is a viewport. Compare the element's aspect against plausible source aspects (3:2, 4:3, 1:1, 9:16).
4. Corner geometry: picsart_media_inventory_diff (reference as a, your candidate as b, same frame size, times of interest; it spends credits) reports whether corners are rounded against the local surround. A rounded photographic corner means a mask or a rounded_corners look, not a rounded photo. Leave plate at auto for cards over a uniform background; with it off, a pale-topped card can split into two invented elements.

What to author once identified: the FULL asset plus a mask (or the look that owns the shape), never a pre-cut bitmap. The mask can then animate and the photo can be replaced. Source ONE full-size asset, not a sliver cut to the mask's current opening: two slots showing one photo at two scales bind the SAME URL, differing only by the host layer's scale.

Never take pixels from the reference clip itself as an asset; use what the user supplied, and a stand-in only when none was.

Debug heuristic

A styled card shows square edges but sibling cards are fine: suspect THIS asset's alpha (swap the photo first, the scene second). A masked thing renders tiny or misplaced: mask plus explicit bounds on one layer (use a boxed aux composition with a bounds-less masked layer inside). Content invisible at layer start: fade-in or decode timing, start later.