You have an exceptionally large video to present to site visitors. As each visitor’s connection reliability and bandwidth are unknown and unpredictable, you want to show them a still image preview of the video (which will load more quickly) until the video has finished loading or has sufficiently buffered.
Across a Manifest and its resources, you may use more than one
placeholderCanvas, allowing you to have an authentic
placeholderCanvas for each appropriate resource (Collection, Manifest, Canvas, and Range).
The target of the Annotation of a
placeholderCanvas should have as its value the id of the
placeholderCanvas, not the id of the resource that has the
Always keep in mind the wide latitude given conforming clients: It is up to the client whether and in what sort of UI to display content you place in a
placeholderCanvas property. Do not use this property for content that must be displayed. On the other hand, placing content in a
placeholderCanvas does communicate to a conforming client that the content, if displayed, should be displayed before the resource to which it is attached.
Each instance of
placeholderCanvas may only contain one Canvas, and as such may specifically not contain an additional
placeholderCanvas or an
In the example, the main content is a video of a performance of Donizetti’s L’elisir d’amore and the
placeholderCanvas is a still frame from the video. For a site visitor with limited bandwidth, showing the still frame allows them to get an advance look at performance aspects such as costuming, staging, and set design.
placeholderCanvas property is not yet supported in viewers.