Caption animation speed in and out: Sume motion overrides

To change how fast burned-in captions animate in and out on Sume, set the motion group of design: enter_seconds, exit_seconds, emphasis_in_seconds and emphasis_out_seconds. All four are durations in seconds, optional, and merge over the style's own timing.

Facts are from Sume's Video captions docs, read 2026-10-01. Blackmagic's 2026-09-08 release, for context, says Cloud Presentations has been updated with subtitle support.

What does each motion field time?

The API schema describes them as the phrase enter and exit durations and how long the spoken token takes to take and release emphasis. Each accepts 0 to 2 seconds; an out-of-range number is a 400 and nothing bills.

Which styles have motion to tune?

Styles with visible motion in the docs include pill-karaoke (colour tracks the voice) and weight-shift (the spoken word takes the weight). design is not supported on punch or tiktok-green. See Descript-style in and out animation for the same group from a different query.

What does a request look like?

Send only the key you want to change.

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-motion-001" \
  -d '{
    "video_url": "https://example.com/clean.mp4",
    "style": "pill-karaoke",
    "language": "ko",
    "design": { "motion": { "enter_seconds": 0.2 } }
  }'

Can I compare timings without paying for a second transcript?

Yes. Pass source_caption_id instead of video_url with a new design. Sume reuses the word timings, so no second speech-to-text runs. Each restyle still renders and bills as a caption job.