AVP also supports subtitles for streamed video assets. The subtitles must be of type text/vtt and stored as file variants with the original video asset and have a filename which is suffixed by the contained locale tag:

The language is taken from the file name, not from the file content. Everything after the last underscore of the name is read as the language tag, so my-video_en.vtt is offered as English and my-video_pt-BR.vtt as Brazilian Portuguese. Both the plain language and the language-REGION form work.

Two consequences are worth knowing when a subtitle does not show up as expected:

• A file whose name contains no underscore is skipped entirely and is never offered as a subtitle track.
• A suffix that is not a valid language tag is not reported as an error. The track is offered, but with no language attached, so the player lists it unnamed.

Only the original rendition of each variant is used, and the mime type has to be exactly text/vtt — a subtitle stored in another format next to the video is ignored.