Tampermonkey / Greasemonkey script to force high quality video on Twitter

twitter_video_hq_tampermonkey.js

// ==UserScript==
// @name         Load HQ Video on Twitter
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Forces Twitter to always load the highest bitrate video available.
// @author       Graham Sutherland
// @match        https://twitter.com/*
// @icon         https://www.google.com/s2/favicons?domain=twitter.com
// @grant        none
// ==/UserScript==

/*

This works by hooking XMLHttpRequest with a custom readystatechange event listener whenever a request is opened to an M3U8 playlist target.
The playlist being targeted contains a list of streams for various bandwidths. The event listener modifies the response to remove all but the highest bandwidth stream.
For safety, two M3U8 rewriting methods are defined. The primary one is a regex, which allows us to find the stream with the greatest bandwidth.
If the regex parsing fails, e.g. due to a format change, the fallback method simply removes all streams but the last one in the list, which is usually the highest bandwidth one.

*/

(function(open) {
    XMLHttpRequest.prototype.open = function() {
        if (arguments[1].match(/\/pl\/[a-zA-Z0-9_]+\.m3u8\?/))
        {
            console.log("Attaching readystatechange event for video playlist XHR.");
            this.addEventListener("readystatechange", function() {
                if (this.readyState == 4)
                {
                    if (this.responseText.startsWith("#EXTM3U"))
                    {
                        console.log("Handling M3U response for video...");
                        var m3u8info = this.responseText;
                        var m3u8new = "";

                        // re-define the response properties as writable
                        Object.defineProperty(this, 'response',     {writable: true});
                        Object.defineProperty(this, 'responseText', {writable: true});

                        // use regex to match stream info
                        var results = m3u8info.matchAll(/^#EXT-X-STREAM-INF:.*BANDWIDTH=(?<bandwidth>\d+),RESOLUTION=(?<resX>\d+)x(?<resY>\d+),CODECS="(?<codecs>[^"]+)"\r?\n(?<url>\/.*\.m3u8)/gm);
                        results = Array.from(results);

                        // attempt to extract stream info with regex to get the highest bandwidth option
                        var gotResultsFromRegex = false;
                        var indexOfFirstMatch = -1;
                        var maxBandwidth = -1;
                        var maxBandwidthIndex = -1;
                        var currentIndex = -1;
                        for (const match of results)
                        {
                            //console.log(match);
                            currentIndex++;
                            gotResultsFromRegex = true;
                            if (indexOfFirstMatch == -1)
                            {
                                indexOfFirstMatch = match.index;
                            }
                            var bw = parseInt(match.groups["bandwidth"], 10);
                            if (bw > maxBandwidth)
                            {
                                maxBandwidth = bw;
                                maxBandwidthIndex = currentIndex;
                            }
                        }

                        // if this succeeded, use the regex results.
                        if (gotResultsFromRegex)
                        {
                            console.log("Stream index " + maxBandwidthIndex + " has the highest bandwidth. BANDWIDTH=" + maxBandwidth + ", RESOLUTION=" + results[maxBandwidthIndex].groups.resX + "x" + results[maxBandwidthIndex].groups.resY + ", CODECS=" + results[maxBandwidthIndex].groups.codecs);
                            m3u8new = m3u8info.substring(0, indexOfFirstMatch) + results[maxBandwidthIndex][0];
                        }
                        else
                        {
                            console.log("Warning: failed to get results from regex. Falling back to line-splitting method.");
                            // split the lines around #EXT-X-STREAM-INF. the first element will be everything before the first stream info, the last element is usually the highest bandwidth
                            var lines = m3u8info.split(/\r?\n#EXT-X-STREAM-INF/);
                            m3u8new = lines[0] + "\n#EXT-X-STREAM-INF" + lines[lines.length - 1];
                        }
                        //console.log(m3u8new);
                        this.response = this.responseText = m3u8new;
                        console.log("Re-wrote M3U8 response to use highest bandwidth stream.");
                    }
                }
            });
        }
        open.apply(this, arguments);
    };
})(XMLHttpRequest.prototype.open);