Suggest use of captions when only alt text provided for video

[str4d]

Describe the Feature

Alt text is viewable in the app UI for images, but not for videos; alt text is only included for screen readers, and captions are supposed to be used for visual display on videos.

If a user attempts to upload a video and has set alt text but provided no captions file, it might be useful to alert them before upload that their alt text will not be visible, and to suggest creating a captions file. (Maybe also let the user dismiss this alert from showing up more than once, as it's an informative help message rather than a persistent reminder?)

Attachments

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Describe Alternatives

Instead of just alerting, it could be nice to have a post editor UI that helps a user prepare a captions file.

Additional Context

No response

[daira]

As someone who doesn't use a screen reader but has auditory processing disorder and watches everything with captions whenever possible, I'd really appreciate being able to see the alt text if that's what has been provided.

Creating a caption file is a lot of work for the skeeter when they only have a transcript. By all means have the prompt that suggests creating one, but if alt text is provided then I don't see any reason why there can't be a way to expand it in the UI without needing screen-reader software. Accessibility can help everyone! (Suppose you just want to paste the text somewhere, for example.) I guess that would be a separate ticket to this one, though. [Edit: I couldn't find an existing ticket so I filed #5959.]

Another important complementary feature: #5946 (Alt Text Require should apply to videos).

For how alt text is represented in the HTML see #5418.

Increasing the alt text character limit: #4998