TikTok Smart Split vs Sume: turn a long video into vertical clips

Smart Split is a TikTok Studio Web tool that automatically clips, reframes, captions and transcribes a longer video into several short videos, and Sume can do the cutting, cropping and captioning steps through its API but does not choose the moments for you. If you want one-click clip picking inside TikTok, use Smart Split; if you need a repeatable pipeline you control, use Sume's trim, filter and captions endpoints.

TikTok's description is from its newsroom post New AI-powered tools to make it easier to create and share on TikTok, dated October 28, 2025 and read 2026-10-02. Sume facts come from Video trim, Video filter, Video captions and Video inspect.

What does Smart Split do?

Per the newsroom post, it accepts videos over one minute, lets you select portions to convert, offers customisable caption formatting and vertical reframing, and can upload generated clips directly to your account. It was listed as globally available on TikTok Studio Web at launch; the post is nearly a year old, so check your own Studio for current availability.

Which Smart Split steps map to Sume?

Sume has an endpoint for each mechanical step, but the sequence is yours to orchestrate.

How do I cut one clip and crop it to 9:16?

Trim first, then crop. A 16:9 frame cropped to a centred 9:16 column keeps 31.6% of the width (9/16 divided by 16/9 is 0.3164), so width is about 0.316 and x is about 0.342 to centre it. Crop width and height are fractions of the frame, and the compiler even-rounds for yuv420p. The filter source ceiling is 300 s, so crop short clips, not the whole talk.

curl -X POST https://api.sume.com/v1/video-filter \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: crop-916-001" \
  -d '{"video_url":"https://media.sume.com/artifacts/artf_demo/clip.mp4","ops":[{"op":"crop","x":0.342,"y":0,"width":0.316,"height":1}]}'

What is the catch?

A fixed centre crop does not follow a speaker who moves, because the crop rectangle is static for the clip. Smart Split's reframing is described as automatic, and Sume's docs do not describe subject tracking, so I will not claim it. Run captions after the crop so the text sits inside the new frame.

Sources over 1800 s fail trim with source_duration_exceeded, and every input must already be on media.sume.com, imported with POST /v1/media-imports. For the long-file caption path see add captions to a long video by API.