Can I use these with the MP4 samples?

Yes. Add the file with a element to check that captions appear, though the text is unrelated to the picture.

What is the MIME type of a VTT file?

The MIME type is text/vtt. The file extension is .vtt.

Is a sample VTT file the same as a dummy or example VTT file?

Yes. Sample, test, dummy and example VTT files are different names for the same thing: a VTT file with known contents that stands in for a real one. Any file on this page will do wherever a tutorial or a test plan asks for a dummy VTT file.

Free VTT sample files

The web standard for captions and subtitles, used by the HTML <track> element. Download valid VTT test files in 4 exact sizes, from 1 KB to 1 MB, each with a checksum.

Extension: .vtt
MIME type: text/vtt
Kind: Text
Category: Subtitles

VTT files by size

Every file below is a valid WebVTT subtitles file of exactly the stated size. Open a file's page for its checksum and contents, and to preview it in your browser before downloading.

VTT sample files by size
File	Size	Contents	Download
1 KB VTT samplesample-vtt-1kb.vtt	1 KB1,024 bytes	Cues: 8	Download VTT
10 KB VTT samplesample-vtt-10kb.vtt	10 KB10,240 bytes	Cues: 88	Download VTT
100 KB VTT samplesample-vtt-100kb.vtt	100 KB102,400 bytes	Cues: 880	Download VTT
1 MB VTT samplesample-vtt-1mb.vtt	1 MB1,048,576 bytes	Cues: 8,940	Download VTT

What is a VTT file?

WebVTT is the caption format built into browsers. A file starts with the word WEBVTT and then lists cues, each with a time range and text, optionally with positioning and styling.

It closely resembles SRT but is formally specified, and supports comments, cue settings and metadata tracks.

How to recognise a VTT file

57W45E42B56V54T54T

The first bytes of every file.

Extension	.vtt
MIME type	text/vtt
Standard	W3C WebVTT
Header	The file must begin with WEBVTT
Timestamp	HH:MM:SS.mmm with a full stop before milliseconds
Encoding	UTF-8 only

What to test for

These are the behaviours that most often go wrong when software handles VTT files.

Browsers load caption tracks under the same cross-origin rules as scripts, so a .vtt file on another domain needs CORS headers.
Servers that send WebVTT as text/plain may see tracks ignored; the correct type is text/vtt.

Strengths of VTT

The native caption format of the HTML video element.
Formally specified, with positioning, styling and comments.

Limitations of VTT

Less widely accepted than SRT outside the browser.
Must be UTF-8 and served with the correct content type.

Typical uses of VTT test files

Testing HTML video captions
Checking subtitle conversion
Testing accessibility of video players

Software that opens VTT

All browsers through the <track> element
Video.js, hls.js and Shaka Player
Streaming platforms

Specifications

W3C WebVTT

VTT sample files: questions

Can I use these with the MP4 samples?: Yes. Add the file with a <track> element to check that captions appear, though the text is unrelated to the picture.
What is the MIME type of a VTT file?: The MIME type is text/vtt. The file extension is .vtt.
Is a sample VTT file the same as a dummy or example VTT file?: Yes. Sample, test, dummy and example VTT files are different names for the same thing: a VTT file with known contents that stands in for a real one. Any file on this page will do wherever a tutorial or a test plan asks for a dummy VTT file.