Burned-in caption text size and outline: Sume design fields

To change the text size and outline of burned-in captions on Sume, send a design.typography object with POST /v1/video-captions. It has six fields: base_weight, active_weight, active_scale, font_size_ratio, safe_width_ratio and stroke_width_px. Each is optional and merges over the chosen style's own value.

This is from Sume's Video captions docs, read 2026-10-01. Subtitle handling is also in the news: Blackmagic's 2026-09-08 release says Cloud Presentations has been updated with subtitle support.

Which fields control caption size and outline?

All six sit in the typography group of design. The API schema gives each a range, shown below; out-of-range numbers return a 400 at request time rather than rendering wrong and billing.

How do I send an override?

Put it under design next to a style. Only the keys you send change; everything else keeps the style's value. Colours go in the colors group of the same object, as in customize burned-in captions.

curl -X POST https://api.sume.com/v1/video-captions \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: caption-typography-001" \
  -d '{
    "video_url": "https://example.com/clean.mp4",
    "style": "black-outline",
    "design": { "typography": { "stroke_width_px": 6 } }
  }'

Which styles can I use this on?

Use slam or a Hangul identity. punch and tiktok-green do not read design at all; the reason is in that note.

Do font and size interact?

font picks the face and design edits the look, so they stack. Two caveats from the docs: weight-shift and korean-ad animate the wght axis, which only Pretendard carries, so on a static face they lose the weight travel and keep colour and scale. And editorial-emphasis draws its emphasis line in Black Han Sans whatever font says.

A bad value is a 400 before the job is accepted. To try sizes on one video, pass source_caption_id instead of video_url; no second transcription runs and the restyle bills as a render.