Renders an element as a base64-encoded JPEG (no data-URL prefix), or null when it cannot (not rendered, tainted canvas, and so on). Must not throw; a channel treats a rejection as "no frame".
null
Renders an element as a base64-encoded JPEG (no data-URL prefix), or
nullwhen it cannot (not rendered, tainted canvas, and so on). Must not throw; a channel treats a rejection as "no frame".