SRT vs VTT: what's the difference?
SRT vs VTT comes down to where the subtitles are going. Both are plain-text files with a time range and words for each caption. VTT is the format web video players need. SRT is the one that works nearly everywhere else, from VLC to TVs to editing software.
What the files look like
An SRT caption is a number, a time line such as 00:00:01,000 --> 00:00:03,500, the words and a blank line. A VTT file starts with the line WEBVTT, uses a dot before the milliseconds (00:00:01.000), and doesn't need the numbers. That comma-versus-dot difference is why a player sometimes rejects a file that looks fine.
What VTT can do that SRT can't
VTT can place a caption on screen, set its width and alignment, name the speaker with a voice tag, and take styling from the web page. SRT has a few simple tags such as <i> for italics, and that's about it. Most of VTT's extras only show in web players.
Which one to use
For an HTML5 video on a website, VTT, because the browser's <track> element only reads VTT. For VLC, Plex, a TV or a video editor, SRT. For uploading, YouTube and Vimeo take both, and Facebook and LinkedIn ask for SRT.
How to convert
SRT to VTT adds the header and swaps the commas for dots. VTT to SRT does the reverse, dropping the VTT-only settings SRT can't hold. Neither one uploads your file.
Questions
Is VTT the same as WebVTT?
Yes. WebVTT is the full name; .vtt is the file extension.
Can I just rename .srt to .vtt?
Not reliably. The header and the decimal separator differ, so many players reject a renamed file. Convert it instead.
Which format does YouTube give me?
Automatic captions usually come as VTT. YouTube transcript gets them as SRT or text too.