SP.Video.EmbedCodeConfiguration.previewImagePath property (sp.documentmanagement)
Gets or sets the URL for the preview image to display before the media plays.
var value = SP.Video.EmbedCodeConfiguration.get_previewImagePath()
SP.Video.EmbedCodeConfiguration.set_previewImagePath(value)
Return value
The string that specifies the URL.
Remarks
Use this property if the default preview image for the media is not appropriate for the current context.