requestThumbnails
open fun requestThumbnails(requests: List<ThumbnailRequest>, callback: ThumbnailBatchCallback): Cancellable(source)
Asks for a run of frames, which a strip fetches together.
Returns immediately and each frame arrives on callback, in the order requests lists them, one call per entry. Frames are produced one at a time, so a source that holds a decoder open across the run serves the whole strip on one setup rather than on one per frame.
Cancelling the returned handle stops the run where it is, and the entries not yet delivered never are. The default walks requests through requestThumbnail, which is what a source with nothing to reuse between frames wants.
Return
a handle that cancels the rest of the run.
Parameters
requests
Which frames, at what sizes, in the order they should arrive.
callback
Receives each frame, or its failure, exactly once.