Using Caption Files with Video Content

Use Case

Captions are available for your video content and you want to enable them for display on top of your IIIF video resources.

Implementation notes

Caption markup file formats use time tags that allow for time alignment and synchronized display of the video content with the captions. Captions are typically overlaid on top of the video. IIIF media viewers can best support all people experiencing multimedia content by supporting both WebVTT and SRT formats for caption files wherever possible.

Offering the caption file as an Annotation on the Canvas that contains the media file itself enables us to express the relationship between the two. The type and format properties of the Annotation can be used by the client to identify caption files to be rendered on top of video content. The format property of the Annotation can also be used to verify that the file is in a usable format. The motivation value of supplementing indicates the fact that this Annotation is in addition to the media resource.

In addition to this implementation, you can also offer captions as multiple timed annotations, making the text available in multiple ways. See [Using Annotations for Timed Text][0079].

While transcripts, captions, and subtitles each present some text interpretation of the A/V content, the ways in which they are consumed by users differ. For a more detailed discussion about these differences see Transcripts, Captions, and Subtitles - General Considerations.

Restrictions

When using segmented WebVTT with HLS, see [Serving HLS Files][0257].

Example

In this example we use a caption file in the WebVTT format. Other options include the SRT (SubRip Text) or TTML (Timed Text Markup Language) formats, or other text-based formats used for the same purpose.

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