ニコニコの動画を矢印キーで数秒進めたり戻したりできるやつ

nicomoveframe.user.js

// ==UserScript==
// @name         Niconico move frame
// @namespace    https://abcang.net/
// @version      0.1
// @description  move frame on niconico video to press arrow key
// @author       ABCanG
// @match        http://www.nicovideo.jp/watch/*
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    function Player() {
        this.player = document.getElementById('external_nicoplayer');
        this.nextTime = 15;
        this.prevTime = 10;
        this.player.addEventListener('keydown', function(e) {
            if (e.keyCode == 39) {
                this.nextFrame();
            } else if(e.keyCode == 37) {
                this.prevFrame();
            }
        }.bind(this));
    }

    Player.prototype.nextFrame = function() {
        var playtime = this.player.ext_getPlayheadTime();
        var totalTime = this.player.ext_getTotalTime();
        var next = Math.min(playtime + this.nextTime, totalTime);
        this.player.ext_setPlayheadTime(next);
    };

    Player.prototype.prevFrame = function() {
        var playtime = this.player.ext_getPlayheadTime();
        var prev = Math.max(playtime - this.prevTime, 0);
        this.player.ext_setPlayheadTime(prev);
    };

    window.addEventListener('load', (function() {
        var player = new Player();
    })(), false);
})();

コメント入力中にも動作するので注意