/**
 * High-sensitivity camera constraints for live barcode / QR decode.
 * Prefer rear camera + high ideal resolution so small symbols fill pixels.
 *
 * Do not set hard `min` width/height - Android Chrome often rejects those with
 * OverconstrainedError. Some Android builds also surface soft-constraint failure
 * as NotAllowedError; the ladder retries NotAllowed only until the final
 * `video: true` rung (a true user deny there is not retried).
 */
export declare const SCANNER_VIDEO_CONSTRAINTS: MediaTrackConstraints;
/**
 * Progressive getUserMedia ladder for mobile browsers.
 * Soften resolution first, then facingMode-only, then any camera.
 */
export declare const SCANNER_VIDEO_CONSTRAINT_FALLBACKS: ReadonlyArray<MediaTrackConstraints | true>;
/**
 * Optical zoom policy for scanner tracks: use the device's capability max
 * (not a hard 2x ceiling). Documented for callers; resolution is via
 * resolvePreferredOpticalZoom.
 */
export declare const SCANNER_OPTICAL_ZOOM_POLICY: "max";
/**
 * Resolve preferred optical zoom from MediaTrackCapabilities.zoom bounds.
 * Targets device max (G2) - no fixed 2x ceiling. Snaps down to a valid step
 * when `step` is provided.
 */
export declare function resolvePreferredOpticalZoom(min: number, max: number, step?: number): number;
/**
 * Midpoint zoom for a stepped ladder toward max (G4 distance lever).
 * Snaps to step when provided.
 */
export declare function resolveMidOpticalZoom(min: number, maxTarget: number, step?: number): number;
/**
 * Open a camera stream with progressive constraint fallbacks.
 *
 * Overconstrained / NotFound / NotReadable / Abort -> next rung.
 * NotAllowedError -> next rung only while `video` is not yet the final `true`
 * (any-camera) rung; on that last rung NotAllowed is a real deny and is rethrown.
 * Other failures (SecurityError, etc.) are rethrown immediately.
 */
export declare function openScannerMediaStream(getUserMedia: MediaDevices['getUserMedia']): Promise<MediaStream>;
/**
 * Best-effort continuous autofocus + torch after getUserMedia.
 * Optical zoom is NOT applied here — max zoom on open blurs/crops close barcodes
 * (camera shows a sharp code but @zxing never locks). The hook applies
 * {@link applyScannerDistanceZoom} only after multi-pass has already started
 * (second assist window), never at open and never at the first assist tick.
 */
export declare function applyScannerTrackEnhancements(track: MediaStreamTrack): Promise<void>;
/**
 * Delayed distance lever (G2/G4): mid → max optical zoom from capabilities.
 * Hook policy: call only after SCANNER_DISTANCE_ASSIST_DELAY_MS (multi-pass first)
 * plus SCANNER_DISTANCE_ZOOM_DELAY_MS — never on open and never at the first
 * assist tick, so close codes with slow AF are not forced into max zoom.
 */
export declare function applyScannerDistanceZoom(track: MediaStreamTrack): Promise<void>;
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