Videos
video embeds a video on a page. The source is either a local file (typically .mp4, copied into _wdoc/ at build time like an image) or a web URL — YouTube, Vimeo, or any other embeddable address. To keep a page light, a video first renders as a click-to-play *facade* (a poster thumbnail plus a play button); the real player loads only when the reader clicks.
Served, not opened directly
A local video is referenced by a relative _wdoc/ URL, so it only resolves when the site is served or hosted — not when the page is opened directly from disk (same as images and icons).
A local file
Give video a doc-relative path and an optional poster thumbnail. Set width to size it, title for an accessible label. Click the poster to play. Live (a short Big Buck Bunny excerpt, © Blender Foundation, CC-BY):

page about { sites = [:demo]
video "assets/intro.mp4" {
poster = "assets/intro-thumb.jpg"
title = "Product intro"
width = 640.0
}
}
No frame extraction
wdoc never decodes a local video, so it can't auto-generate a thumbnail. Supply a poster image; without one, a plain play-button placeholder shows.
YouTube & Vimeo
A YouTube or Vimeo URL is recognised automatically and embedded as a privacy-respecting click-to-play iframe. For YouTube, the poster thumbnail is derived from the video id when you don't supply your own. Live:

video "https://www.youtube.com/watch?v=aqz-KE-bpKQ" { title = "Trailer" }
video "https://vimeo.com/76979871" {
poster = "assets/vimeo-thumb.jpg" // Vimeo has no auto-thumbnail
title = "Our talk"
}
Any other embed
Any other http(s) URL is embedded verbatim in an iframe (the *generic* form). A URL ending in a video extension (.mp4, .webm, …) instead plays natively in a <video> element.
video "https://example.com/player/embed/abc" { title = "Hosted clip" }
video "https://cdn.example.com/clip.webm" { title = "Direct file" }
In PDF output
A PDF can't play video, so wcl wdoc pdf renders the poster thumbnail and — for an online video only — a link to it. A local video shows just its poster (a path to a local file is useless in a distributed PDF).
Fields