OptionalBuildWhen true, also compose extracted keyframes into tiled contact-sheet PNGs for non-video-input models.
OptionalMaxMaximum number of keyframes to extract (defaults to 16).
MIME type of the reference video (e.g., 'video/mp4', 'video/webm').
Base64-encoded reference video bytes (MP4/WebM) to sample.
Request to sample keyframes from a reference video via FFmpeg scene-change and uniform sampling.