SRT — the universal default
SubRip. Cue number, comma-millisecond timecodes, plain text with optional <i>/<b> tags. Accepted by YouTube, Vimeo, VLC, Plex, Premiere, DaVinci, Final Cut (via plugins) and nearly every LMS. If you are unsure, deliver SRT.
VTT — the web standard
WebVTT is what the HTML5 <track> element expects, so web players, Vimeo, Wistia, JW Player and most course platforms want it. It starts with a WEBVTT header, uses dot-milliseconds, and supports cue settings (position, alignment) and STYLE blocks. Converting SRT → VTT is lossless; VTT → SRT drops positioning.
SBV — YouTube's export
A simplified format YouTube produces when you download captions: start,end on one line, then text. Almost nothing else reads it, so convert to SRT if you need the file anywhere but YouTube.
ASS/SSA — styling and typesetting
Advanced SubStation Alpha carries fonts, colours, positions, karaoke and animation. It is the standard for anime fansubs and anything made in Aegisub. Players like VLC and mpv render it; YouTube does not accept it. Converting ASS → SRT keeps italics/bold and drops everything else.
SMI — the Korean legacy format
SAMI is an HTML-like format that was standard for Korean video for two decades. Korean players (Pot Player, GOM) still read it; nothing modern outside Korea does. Convert SMI → SRT for YouTube or web use.
Converting without losing timing
All five formats store absolute times, so conversion is a matter of rewriting the syntax; a good converter keeps millisecond precision (ASS rounds to centiseconds). What you can lose is styling and positioning when going to a simpler format. Convert first, then translate, so the translator sees the format you will actually publish.
Tools mentioned
Questions
- Can YouTube use VTT?
- Yes, YouTube accepts SRT, VTT, SBV and several others. It does not accept ASS/SSA or SMI.
- Is converting SRT to VTT lossless?
- Yes. VTT is a superset for plain cues. The reverse loses cue settings such as position and alignment.
- Why does my SMI file show garbled text?
- Legacy SMI files are often saved in EUC-KR. Re-save as UTF-8 before converting or translating.