/**
 * Loop-match filter builder for Shorts.
 *
 * YouTube Shorts auto-replays from the start when the clip ends. A
 * crossfade between the last N ms and the first N ms makes the
 * re-loop feel seamless. Loop rate is a confirmed Shorts ranking
 * signal — see the `youtube-algorithm-primer` skill.
 *
 * This module produces the `-filter_complex` string and the matching
 * `-map` directives. The wrapper tool then runs ffmpeg with libx264 +
 * aac at standard delivery settings.
 *
 * Two modes:
 *   - "crossfade" (default): xfade fade between the tail and a copy of
 *     the head. Audio: acrossfade.
 *   - "jumpcut": no crossfade — simply hard-cut the last cf seconds off
 *     so the loop boundary lands right before the head's first frame.
 *     Cheaper; safe for very short clips where any crossfade would eat
 *     too much of the visible content.
 */
export type LoopMatchMethod = "crossfade" | "jumpcut";
export interface LoopMatchPlan {
    /** Effective crossfade duration after clamping. */
    crossfadeSec: number;
    /** Final output duration after the filter applies. */
    outDurationSec: number;
    method: LoopMatchMethod;
    /** ffmpeg -filter_complex value. */
    filter: string;
    /** -map directives in order. */
    maps: string[];
}
/**
 * Build the filter graph for a loop-match pass.
 *
 * crossfade mode plan:
 *   [0:v] split=2 [main][tail_src];
 *   [main]   trim=0:T-cf, setpts=PTS-STARTPTS [vmain];
 *   [tail_src] trim=T-cf:T,  setpts=PTS-STARTPTS [tail];
 *   [0:v] trim=0:cf, setpts=PTS-STARTPTS [head];
 *   [tail][head] xfade=transition=fade:duration=cf:offset=0 [xfade];
 *   [vmain][xfade] concat=n=2:v=1:a=0 [vout]
 *   ── audio ──
 *   [0:a] asplit=2 [amain][atail_src];
 *   [amain]    atrim=0:T-cf, asetpts=PTS-STARTPTS [aout1];
 *   [atail_src] atrim=T-cf:T, asetpts=PTS-STARTPTS [atail];
 *   [0:a]      atrim=0:cf,    asetpts=PTS-STARTPTS [ahead];
 *   [atail][ahead] acrossfade=d=cf [axfade];
 *   [aout1][axfade] concat=n=2:v=0:a=1 [aout]
 *
 * Final length = (T - cf) + cf = T. Duration unchanged; only the last
 * cf seconds become a crossfade into the head.
 *
 * Pure — easy to unit-test the filter string. Throws on invalid input.
 */
export declare function buildLoopMatchFilter(durationSec: number, crossfadeSec: number, method?: LoopMatchMethod): LoopMatchPlan;
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