VTT: Metadata Track With JSON Payloads
A WebVTT metadata track whose cue payloads are JSON objects rather than text for display. This is how timed analysis output (scene changes, detections, speech segments) is carried alongside a video and read from JavaScript via the cue change event. Nothing here should ever be rendered on screen.
WEBVTT
NOTE Metadata track — cue payloads are JSON, not display text.
00:00:01.000 --> 00:00:03.000
{"event":"scene-change","confidence":0.94}
00:00:05.000 --> 00:00:07.000
{"event":"face-detected","count":2,"boxes":[[10,20,80,90],[120,30,60,70]]}
00:00:09.000 --> 00:00:11.000
{"event":"speech","speaker":"A","words":12}
Specifications
- Kind
- metadata
- Cues
- 3
- Payload
- JSON per cue
- Alt Text
- A WebVTT metadata track whose cue payloads are JSON objects rather than text for display
- Alt Text Source
- description
Testing contract
Expected to pass- Scenario
- Attach the file as a metadata track and parse each cue payload.
- Expected result
- 3 cues whose payloads are JSON rather than display text. A metadata track must never be rendered to the screen - the browser will not display `kind="metadata"` cues, and code that falls back to treating unknown tracks as subtitles will print raw JSON over the video.
What is a .vtt file?
WebVTT (VTT) is the W3C subtitle and caption format used by the HTML5 <track> element for timed text on the web. It extends the SubRip model with cue settings, positioning, styling, and metadata, and requires a WEBVTT header. It is the standard format for browser-based captions.
How to use this file
Use an example VTT to test HTML5 <track> caption rendering, cue-setting and positioning parsers, and converters between WebVTT and SRT.
How to use this file for testing
“VTT: Metadata Track With JSON Payloads” is a deterministic Testaroo fixture for Subtitle parsing, Video QA, Streaming manifests. The same captions written out across SubRip, WebVTT, ASS/SSA, SBV, TTML and a synced LRC lyric file, with known timings, for exercising subtitle parsers, format converters and burn-in tools against every serialisation.
Documented properties for this file: 3 cues. Compare results against paired or grouped companions on this page when present (clean↔damaged, searchable↔scanned, or format twins) so scores stay reproducible across runs.
Download the file once, keep the path stable in CI or local scripts, and treat the spec table as the contract: dimensions, seeds, field lists, and roles are intentional. Corrupt or invalid samples are labelled as such, expect parsers to fail loudly rather than silently accept them.
Media fixtures are short and synthetic by design. Prefer waveform or transcript ground truth in the same group when measuring ASR, trim, upscale, or sync tools; do not assume broadcast-quality masters.
Parse the cues and check timings against the documented count; the same captions ship across subtitle formats so you can diff a converter against a known target.
Code examples
<video controls src="clip.mp4">
<track kind="captions" srclang="en" label="English" src="metadata.vtt" default>
</video>Generated by generation/video_timedtext.py. Free for any use, no attribution required, license.
Related files
- vttThumbnail Track: WebVTT Sprite IndexThe WebVTT half of a scrub-preview pair: each cue covers a slice of the timeline and its payload is a media-fragment URL naming a rectangle of the sprite sheet. This is how seek-bar previews are delivered in practice, and the #xywh fragment syntax is the part players implement inconsistently: some resolve it relative to the VTT, others to the page, and some ignore the fragment entirely and show the whole sheet.
- csvCSV: Cue Timing ReportPer-cue timings and text metrics for the shared cue list, as a caption QC tool would export them: start, end, duration, line count and character count. Useful as the expected output when testing a caption analyser, and as a quick way to check reading-rate calculations against known values.
- m4sDASH VOD: Init Segment (init-stream0.m4s)A DASH initialisation segment carrying codec configuration for one representation. Named by the manifest's $RepresentationID$ template, so this file also exercises whether a client resolves template variables correctly rather than pattern-matching filenames.
- m4sDASH VOD: Init Segment (init-stream1.m4s)A DASH initialisation segment carrying codec configuration for one representation. Named by the manifest's $RepresentationID$ template, so this file also exercises whether a client resolves template variables correctly rather than pattern-matching filenames.
- m4sDASH VOD: Init Segment (init-stream2.m4s)A DASH initialisation segment carrying codec configuration for one representation. Named by the manifest's $RepresentationID$ template, so this file also exercises whether a client resolves template variables correctly rather than pattern-matching filenames.
- mpdDASH VOD: Manifest (Playable Package)A complete, playable MPEG-DASH manifest for the same 320x180 at 300 kbps, 480x270 at 700 kbps, 640x360 at 1400 kbps ladder as the HLS package, produced from the same encoder run, so the two can be compared directly as packaging rather than as content. Every segment it references exists in this group. Served inline as application/dash+xml with permissive CORS, so dash.js can load it cross-origin.
