What it means
WebVTT is a timed-text format used with web media tracks. A basic file starts with WEBVTT, a blank line, and timed cues. Its millisecond separator is a full stop.
WEBVTT
00:01.000 --> 00:03.500
Keep the original source.An HTML player can associate a separate text track with video using the track element. The file and player still need to agree on language, track kind and timing.
More than a different extension
The complete WebVTT format can carry cue settings, regions, styling and other content. Some cues can overlap intentionally. Renaming .srt to .vtt does not perform a conversion, and converting complex WebVTT to a simpler format can lose information.
Use the plain-text subset deliberately
The SRT/VTT converter preserves visible plain text and millisecond times. It normalizes cue numbering and newlines. It rejects unsupported settings or markup instead of quietly stripping them. Keep an original copy if your file uses features outside that subset.
Check the actual player
Read the first caption, a middle caption and one near the end beside the video. Check line breaks and any simultaneous captions. A file that parses correctly can still have wrong words or be attached to the wrong video revision.