OptionaldecodeOutput frame resolution: it sizes the decode sink, so frames decode (and paint, and copy) at this width with height following native aspect. Native when omitted; a capped strategy makes a thumbnail pass cheaper end to end rather than decoding native and scaling down afterward.
Optionalpool
Playback-independent analysis over a video source: metadata, keyframe discovery, and frame extraction at arbitrary timestamps. It rides the same opened decode source as the playback cursor but spins no worker, binds no canvas, and runs no clock, so a consumer can pull thumbnails or build a contact sheet without standing up a player.
Extracted frames are copied into their own canvases before the next decode, because the underlying sink recycles a small pool round-robin; the copy is what makes a returned frame safe to hold.