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YouTube 720p

change default YouTube video quality to 720p or highest available below 720p. can be used for other video qualities by changing preferredQuality in the code below.

当前为 2015-03-09 提交的版本，查看 最新版本。

// ==UserScript==
// @name         YouTube 720p
// @namespace    http://www.youtube.com/
// @version      1.4.0
// @description  change default YouTube video quality to 720p or highest available below 720p. can be used for other video qualities by changing preferredQuality in the code below.
// @match        http://youtube.com/*
// @match        https://youtube.com/*
// @match        http://www.youtube.com/*
// @match        https://www.youtube.com/*
// @grant        none
// @run-at       document-end
// ==/UserScript==


youtubeOverride = function (unsafeWindow) {
    
    // qualities = ['auto', 'hd1080', 'hd720', 'large', 'medium', 'small', 'tiny'];
    // set the quality desired here:
    preferredQuality = 'hd720';
    
    console.log('override script starting')
    
    var player = getPlayerAPI();
    if (player != null) {
        overridePlayer(player);
    } else {
        console.log('cannot get player api');
        
        var target = document.getElementById('player');
        var MutationObserver = window.MutationObserver;
        var observer = new MutationObserver(function (mutations) {
            mutations.forEach(function (mutation) {
                if (mutation.target.id === 'player-unavailable')  {
                    console.log('player mutation detected');
                    player = unsafeWindow.document.getElementById('movie_player');
                    if (player != null) {
                        overridePlayer(player);
                    } else {
                        console.log('cannot get player api2');
                    }
                }
            });
        });
        observer.observe(target, { childList: true, subtree: true });
    }
    
    function getPlayerAPI() {
        if (location.pathname.indexOf("/embed/") === 0) {
            return unsafeWindow.yt.player.getPlayerByElement(unsafeWindow.document.getElementById("player"));
        }
        
        return unsafeWindow.document.getElementById('movie_player');
    }
    
    function overridePlayer(player) {
        if (overridePlayer.running) {
            return;
        }
        overridePlayer.running = true;
        
        overrideTimeoutFunc.attempts = 0;
        setTimeout(overrideTimeoutFunc, 300);
        
        function overrideTimeoutFunc() {
            overrideTimeoutFunc.attempts++;
            var success = tryToOverride(player);
            if (!success && overrideTimeoutFunc.attempts < 30) {
                setTimeout(overrideTimeoutFunc, 1000)
            } else {
                overridePlayer.running = false;
            }
        }
        
        function tryToOverride(player) {
            console.log('quality override starting');
            
            if (!('setPlaybackQuality' in player)) {
                console.log('error: setPlaybackQuality not available');
                return false;
            }
            
            var qualityLevels = player.getAvailableQualityLevels();
            var qualityToSet = null;
            for (var i = 0; i < qualityLevels.length; i++) {
                if (qualityLevels[i].trim().toLowerCase() === preferredQuality) {
                    qualityToSet = qualityLevels[i];
                    break;
                }
            }
            if (qualityToSet == null) {
                qualityToSet = qualityLevels[0];
            }
            if (qualityToSet == null) {
                console.log('error: no quality levels available');
                return false;
            }
            player.setPlaybackQuality(qualityToSet);
            console.log('set quality to ' + qualityToSet);
            return qualityToSet == player.getPlaybackQuality();
        }
    }
};

(function () {
    if (this.unsafeWindow != null) {
        youtubeOverride(unsafeWindow);
    } else {
        var scriptElem = document.createElement('script');
        scriptElem.setAttribute('type', 'text/javascript');
        scriptElem.text = '(' + youtubeOverride.toString() + ')(window);';
        
        document.documentElement.appendChild(scriptElem);
        document.documentElement.removeChild(scriptElem);
    }
})();