Which caption file formats does YouTube accept, and which support styling/positioning?

YouTube Help (captured 2026-10-23): basic formats recommended for beginners are SubRip (.srt) and SubViewer (.sbv/.sub), timing-only and editable in plain text. Advanced formats: SAMI (.smi/.sami) and RealText (.rt) with simple markup and no positioning; WebVTT (.vtt) "in initial implementation" with positioning but styling limited to b/i/u; TTML (.ttml, .dfxp; iTT subset) partially implemented; Scenarist (.scc) is YouTube's preferred broadcast format as exact CEA-608. TikTok/Instagram caption documentation not yet retrieved: gap. Curator correction 2026-10-24 (discovery audit record C3-B1064-01, curator-reviewed C3R-0688; excerpts re-located by independent curator GET 2026-10-24): Correction. C3-B336-05 (YouTube Help captured 2026-10-23) answers which formats support styling and positioning but describes TTML only as 'partially implemented' and lists SRT, SBV, SAMI, RT, WebVTT and SCC. The same YouTube Help page, re-read 2026-10-24, says for TTML: 'Styling and positioning are supported' (iTT subset), so the TTML row states 'Styling and positioning are supported' (the sentence follows the iTT-subset sentence, so its scope may be iTT; DFXP files are interpreted as TTML), which the record omits. The record's 'partially implemented' comes from the same page and row ('In partial implementation'), so this is an omission, not a documentation conflict. The Basic table also lists LRC and Videotron Lambda (.cap), and the broadcast section covers CEA-608 and EBU-STL formats, so the record's list is not exhaustive. Inference: the page text probably existed when the record was written (captured 2026-10-23; no page revision date was checked); the omission was material to the question asked, which was about styling and positioning. Other statements in the record match the page. Curator qualifications: All cited excerpts located in the live source text by curator GET 2026-10-23 (bytes hashed, discarded). Limitations: Help/doc pages are undated or change without notice; statements are as served on 2026-10-23. SRV3/YouTube Timed Text upload support not stated on this page. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://support.google.com/youtube/answer/2734698?hl=en",
      "note": "line 24; WebVTT row; line 104"
    }
  ]
}