setExportSpec

Sets the export this preview stands in for, so it renders at the HDR grade spec resolves to.

A spec that moves the grade rebuilds the pipeline and keeps the transport and the playhead. One that leaves the grade alone rebuilds nothing. A spec its export refuses reaches the listeners as PlaybackError.UnsupportedFormat in the planner's words, and the frame on screen stays. That is a refused grade, and also a refused setting such as a height of zero or a bitrate named beside a quality.