Class frame_entry

examples/main_video.cpp:155–157

    // Timeline: per-frame instance presence
    // timeline_instances[frame_index] = list of {instance_id, score}
    struct frame_entry {
        std::vector<std::pair<int, float>> instances; // (id, score)
    };
    std::vector<frame_entry> timeline;
    int                     timeline_max_frame = -1; // highest frame tracked so far
};