TikTok ad account name: 20 characters, and Spark caption: 4 lines

TikTok's In-Feed ads page limits the account name to one line of at most 20 characters, or 10 for CJK text, and shows Spark Ads captions up to 4 lines including emojis. None of that lives in the video file, so Sume cannot set it; you fix it in the ad fields and keep the on-screen text clear of them.

The limits are quoted from TikTok's page (read 2026-10-10). They matter for AI video because the clip, the caption and the account name all appear together in the feed.

The text fields TikTok lists

For non-Spark ads the page says ad captions are displayed in white with a uniform font that cannot be customized. It says the account name displays only one line with a maximum of 10 characters for CJK scripts or 20 characters otherwise. For the profile photo it lists 98 x 98 pixels, square 1:1, jpg, jpeg or png, under 50 KB. For Spark Ads it says a maximum of 4 lines can be displayed, including emojis.

Keeping your own on-screen text separate

The caption white font is TikTok's, so do not design around matching it. Text you burn into the video is yours. Sume's Video captions API takes a public HTTPS video URL and burns captions with a style such as slam, punch, tiktok-green or black-outline. If the clip is silent, speech captions fail with caption_no_speech, and you send authored cues with text, start and end instead.

One practical rule: do not repeat the account name in the burned text. It is already on screen, and it spends characters you do not have.

Rendering the clip to sit under those fields

Timeline 1.0 renders 1080 x 1920 by default, and its width and height can be any even value from 256 to 2160. TikTok's page lists 540 x 960 as a vertical minimum, so either size passes on resolution. The Instagram pages give a safe-zone guide of 14% top, 35% bottom and 6% sides; TikTok's page, in the figures I fetched, gives no such numbers, so I would not borrow Instagram's for TikTok without checking TikTok's own overlay.

A pre-flight list

Count characters with spaces for each field, because the page counts characters, not words. Keep the account name under 20, or 10 if it uses CJK characters. Write the Spark caption so it still reads in four lines. Then render, measure the file, and upload. If your account name is long, a brand rename is cheaper than a re-render.

Because these limits are display limits, they fail quietly. An over-long account name may be cut off rather than refused, and a Spark caption longer than four lines may simply be truncated in the feed. I did not find the exact truncation behaviour on the page, so treat the limits as hard when you write copy. A clean read at the limit is better than a clever line that gets clipped.

If you produce many variants, keep the copy in one sheet with a character count column. The video side is repeatable with Sume, since each render is a job with a duration_seconds result; the text side is where mistakes creep in because it lives in a different tool. One sheet that pairs file name, duration and the two text fields prevents mismatches when a batch goes out.

• Account name: one line, 20 characters.
• Spark caption: four lines including emojis.
• Burned captions: your own, separate from both.