YouTube Shorts safe zone: place burned-in captions with anchor_ratio

YouTube's Shorts editor marks a safe zone for you: drag an overlay too close to the edge and animated white lines appear, signaling a non-safe area where content may be partly hidden on some devices, and icons appear where viewer elements like the like button might sit. Sume's burned-in captions can be moved to match with design.placement.anchor_ratio, a fraction of frame height from 0.05 to 0.95.

YouTube's behavior is from Enhance your Shorts, read 2026-10-02. That page gives no pixel margins, so this post gives none either. Sume's side is the video captions docs.

What does YouTube's own safe zone guide actually say?

Two things. White animated lines show when an overlay is near the screen edge, meaning part of it may be hidden on some devices. Icons show when a sticker or text sits where viewer interface elements, such as the like button, might appear.

It does not publish a numeric rule. So the reliable method is to use the guide in the editor itself, place a test overlay, and note where the lines appear. This is also why captions burned in outside the editor deserve a check before upload: the editor can only warn you about overlays it draws.

Which Sume caption fields control position and width?

Caption styles are sets of design tokens, and design overrides them per request. For position, placement.anchor_ratio sets the line centre as a fraction of frame height, and landscape_anchor_ratio does the same for landscape frames. For width, typography.safe_width_ratio bounds the text block and the API accepts 0.3 to 1.0. Out-of-range numbers return a 400 rather than rendering wrong and billing.

Two styles ignore all of this: design is not supported on punch or tiktok-green, which render on a path that reads none of these tokens. Use slam, black-outline or another style when you need to move the line.

How do I move captions off the bottom edge?

Pick an anchor_ratio that keeps the line well above the bottom controls you saw in the YouTube editor, then narrow safe_width_ratio so lines stay clear of the right-hand icons. Render one test, open it in the Shorts editor as a normal clip, and compare. The values are yours to tune; Sume does not claim a platform-correct default.

A restyle is cheap to repeat because source_caption_id reuses the word timings, though each render is billed.

curl -X POST https://api.sume.com/v1/video-captions \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: short-safe-001" \
  -d '{"video_url":"https://media.sume.com/artifacts/artf_demo/clean.mp4",
       "style":"slam",
       "design":{"placement":{"anchor_ratio":0.6},
                 "typography":{"safe_width_ratio":0.7}}}'

What is not covered?

The 0.6 and 0.7 above are example values, not YouTube-approved numbers. TikTok and Instagram publish their own overlay areas; this page covers only what YouTube's help page says, because that is the one read for this post. Sume does not know where a given phone puts its buttons, and it cannot preview inside the Shorts feed.