---
title: "Important: WebVTT files become uploadable"
manual: "Frontend Theme for Extension Development"
version: "main"
source: "Changelog/2.0/Important-WebVttUploads.rst"
modified: "2026-09-17T04:52:50+00:00"
---

# Important: WebVTT files become uploadable

## Description

The extension appends `vtt` to
`$GLOBALS['TYPO3_CONF_VARS']['SYS']['textfile_ext']` in its
`ext_localconf.php`. This is a change to what the **whole installation**
accepts as an upload, made by a theme, so it is stated here rather than left in
a code comment.

### What exactly changes

| Before | After |
| --- | --- |
| `css,csv,htm,html,js,json,md,rst,rtf,sql,srt,tmpl,ts,txt,typoscript,xlf,xml,yaml,yml` | the same list, with `vtt` appended |

The value is read, split, and written back with one entry added. **Nothing the
core ships is removed, replaced or reordered**, and the entry is added only
when it is not already present - so an installation that already allows
`vtt`, through its own `additional.php` or another extension, is
changed in no way at all. The order of the other extensions' additions is
preserved, because the list is only ever appended to.

### Why this is necessary at all

**Text & Media** gained a **Captions** field for WebVTT caption
tracks - see [Feature: Audio and video in Text & Media](Feature-AudioAndVideoInTextMedia.html#feature-audio-and-video). A caption track is what WCAG 1.2.2
asks of a video, and it is the one part of a media element that is not
decoration.

A file reaches a storage only if its extension is in one of the three lists
`ResourceConsistencyService::getAllowedFileExtensions()` reads -
`textfile_ext`, `mediafile_ext` and `miscfile_ext` \- whenever the
security feature `security.system.enforceAllowedFileExtensions` is on. TYPO3
ships `srt`, the other subtitle format, in `textfile_ext`, and `vtt` in
none of the three. Without this change an editor uploading the file the field
asks for gets **Resource consistency check failed**, a message that
names neither the file nor the extension, and the field can never be filled.
The registration is therefore a prerequisite of the feature, not a convenience
for the demo tree.

`textfile_ext` and not `mediafile_ext`: a WebVTT file is text - the
transcript of a medium, not a medium - and `mediafile_ext` is what
`common-media-types` resolves to, which is the list the **Media**
field accepts. A caption file has no business being offered there.

### Why the extension and not only the development instance

The narrower option was to make the change in the development instances alone,
in their `config/system/additional.php`, so that only the showcase is
affected. That was rejected: it would make the shipped
**Captions** field work in this repository and fail in every
installation that uses the extension, with the misleading error above and
nothing to point at the cause. A field an extension ships has to work where the
extension is installed.

## Impact

An installation using this extension accepts `.vtt` uploads. That is the
intent, and it is the minimum the **Captions** field needs.

If you do not want it, remove the entry again in your own
`additional.php`, which is loaded after `ext_localconf.php`:

```php
$extensions = GeneralUtility::trimExplode(',', $GLOBALS['TYPO3_CONF_VARS']['SYS']['textfile_ext'], true);
$GLOBALS['TYPO3_CONF_VARS']['SYS']['textfile_ext'] = implode(
    ',',
    array_filter($extensions, static fn(string $extension): bool => $extension !== 'vtt'),
);
```

The **Captions** field then stays in the form and refuses the upload,
which is the state the field was in before this change.