Read the actual source requirement
W3C's TTML2 recommendation describes timed-text interchange and presentation with profiles, timing and styling. WebVTT has another defined cue representation.
The broad word subtitles hides those requirements. Identify the supplied format and relevant profile where the legitimate source provides it.
Separate text detection from rendering
A player can recognise that a track exists while failing to render its particular representation or style correctly. A track appearing in a menu is an earlier result than readable timed text.
Conversely, text showing in another app demonstrates that other path, not automatic full support in the first player.
Test a meaningful cue
Use an authorised exact edition and a known passage. Inspect words, timing, placement and needed accessibility information.
A simple one-line cue may not exercise layout or styling used later. Keep the test scope honest instead of turning a brief sample into an all-profile claim.
Do not rename formats as a workaround
Changing an extension does not convert one syntax into another or preserve every style. A legitimate conversion workflow can have its own feature tradeoffs and requires appropriate permission.
Ask the provider or player developer for a supported representation rather than supplying an unverified converter or changing the only copy.
Keep the specification status precise
The cited TTML2 page is a W3C recommendation; the cited 2026 WebVTT document has its own draft status. Neither is a test report for the user's app.
No subtitle file or implementation was inspected here. The article explains format and implementation boundaries without promising a service track or certifying accessibility.
Give support more than an extension
Include track type, stated profile, player/version and the exact failing cue behaviour when known. If profile information is unavailable, leave it unknown rather than guessing from a filename. A source format, a player's declared support and a successful rendered task are three kinds of evidence. Keeping them separate makes a compatibility request useful and prevents an attractive subtitle menu from being treated as proof that every supplied text feature works. If the player developer supports only a stated subset, retain that qualification with the answer. A general subtitle claim should not be expanded into support for every style, timing expression, profile or delivery arrangement in a standard.
Sources and scope
Scope notes distinguish published documentation, supplied information and editorial methods. They do not report a hands-on service test.
- W3C TTML2 recommendation — Official recommendation abstract and document structure inspected: timed-text interchange/presentation, profiles and styling. No player implementation certified.
- W3C WebVTT May 2026 draft — Official versioned excerpt: timed cue format and placement; no guarantee of every draft feature in every app.
- W3C WAI captions — Official current excerpt: captions and timed text context. No accessibility conformance test performed.
