frontend/osu/js/osu-audio.js

define([], function () {
    function syncStream(node) { // https://stackoverflow.com/questions/10365335/decodeaudiodata-returning-a-null-error
        var buf8 = new Uint8Array(node.buf);
        buf8.indexOf = Array.prototype.indexOf;
        var i = node.sync,
            b = buf8;
        while (1) {
            node.retry++;
            i = b.indexOf(0xFF, i);
            if (i == -1 || (b[i + 1] & 0xE0 == 0xE0))
                break;
            i++;
        }
        if (i != -1) {
            var tmp = node.buf.slice(i);
            delete(node.buf);
            node.buf = null;
            node.buf = tmp;
            node.sync = i;
            return true;
        }
        return false;
    }

    function offset_predict_mp3(tags) {
        let default_offset = 22;
        if (!tags || !tags.length) {
            console.warn("mp3 offset predictor: mp3 tag missing");
            return default_offset;
        }
        let frametag = tags[tags.length - 1];
        if (frametag._section.sampleLength != 1152) {
            console.warn("mp3 offset predictor: unexpected sample length");
            return default_offset;
        }
        let vbr_tag = null;
        for (let i = 0; i < tags.length; ++i)
            if (tags[i]._section.type == "Xing")
                vbr_tag = tags[i];
        if (!vbr_tag) {
            return default_offset;
        }
        if (!vbr_tag.identifier) {
            console.warn("mp3 offset predictor: vbr tag identifier missing");
            return default_offset;
        }
        if (vbr_tag.vbrinfo.ENC_DELAY != 576) {
            console.warn("mp3 offset predictor: vbr ENC_DELAY value unexpected");
            return default_offset;
        }
        let sampleRate = vbr_tag.header.samplingRate;
        if (sampleRate == 32000) return 89 - 1152000 / sampleRate;
        if (sampleRate == 44100) return 68 - 1152000 / sampleRate;
        if (sampleRate == 48000) return 68 - 1152000 / sampleRate;
        console.warn("mp3 offset predictor: sampleRate unexpected");
        return default_offset;
    }

    function preprocAudio(filename, buffer) {
        let suffix = filename.substr(-3);
        if (suffix != "mp3") {
            console.log("Preproc audio: ogg", suffix);
            return {
                startoffset: 19
            };
        }
        mp3Parser.readTagsNew = readTagsNew;
        let tags = mp3Parser.readTagsNew(new DataView(buffer));
        if (tags.length == 3 && tags[1]._section.type == "Xing") {
            console.log("Dumbifing", filename);
            let arr = new Uint8Array(buffer.byteLength - tags[1]._section.byteLength);
            arr.set(new Uint8Array(buffer, 0, tags[1]._section.offset), 0);
            let offsetAfter = tags[1]._section.offset + tags[1]._section.byteLength;
            arr.set(new Uint8Array(buffer, offsetAfter, buffer.byteLength - offsetAfter), tags[0]._section.offset);
            buffer = arr.buffer;
            return {
                startoffset: offset_predict_mp3(tags),
                newbuffer: arr.buffer
            };
        }
        return {
            startoffset: offset_predict_mp3(tags)
        };
    }

    //mp3 parser bug fix
    function readTagsNew(view, offset) {
        offset || (offset = 0);
        var sections = [];
        var section = null;
        var isFirstFrameFound = false;
        var bufferLength = view.byteLength;
        var readers = [mp3Parser.readId3v2Tag, mp3Parser.readXingTag, mp3Parser.readFrame];
        var numOfReaders = readers.length;
        for (; offset < bufferLength && !isFirstFrameFound; ++offset) {
            for (var i = 0; i < numOfReaders; ++i) {
                section = readers[i](view, offset);

                //***fix point***//
                if (section && section._section.byteLength) {

                    sections.push(section);
                    offset += section._section.byteLength;
                    if (section._section.type === "frame") {
                        isFirstFrameFound = true;
                        break;
                    }
                    i = -1;
                }
            }
        }
        return sections;
    }

    function OsuAudio(filename, buffer, callback) {
        var self = this;
        this.decoded = null;
        this.source = null;
        this.started = 0;
        this.position = 0;
        this.playing = false;
        this.audio = new AudioContext();
        this.gain = this.audio.createGain();
        this.gain.connect(this.audio.destination);
        this.playbackRate = 1.0;
        this.posoffset = 0;

        let t = preprocAudio(filename, buffer);
        if (t.startoffset) this.posoffset = t.startoffset;
        if (t.newbuffer) buffer = t.newbuffer;
        console.log("Set start offset to", this.posoffset, "ms");
        console.log("You've set global offset to", game.globalOffset || 0, "ms");
        this.posoffset += game.globalOffset || 0;

        function decode(node) {
            self.audio.decodeAudioData(node.buf, function (decoded) {
                self.decoded = decoded;
                console.log("Song decoded");
                if (typeof callback !== "undefined") {
                    callback(self);
                }
            }, function (err) {
                console.log("Error");
                alert("Audio decode failed. Please report by filing an issue on Github");
                if (syncStream(node)) {
                    console.log("Attempting again");
                    decode(node);
                }
            });
        }
        decode({
            buf: buffer,
            sync: 0,
            retry: 0
        });

        this.getPosition = function () {
            return this._getPosition() - this.posoffset / 1000;
        }

        this._getPosition = function _getPosition() {
            if (!self.playing) {
                return self.position;
            } else {
                return self.position + (self.audio.currentTime - self.started) * self.playbackRate;
            }
        };

        this.play = function play(wait = 0) {
            if (self.audio.state == "suspended") {
                window.alert("Audio can't play. Please use Chrome or Firefox.")
            }
            self.source = self.audio.createBufferSource();
            self.source.playbackRate.value = self.playbackRate;
            self.source.buffer = self.decoded;
            self.source.connect(self.gain);
            self.started = self.audio.currentTime;
            if (wait > 0) {
                self.position = -wait / 1000;
                self.source.start(self.audio.currentTime + wait / 1000 / self.playbackRate, 0);
            } else {
                self.source.start(0, self.position);
            }
            self.playing = true;
        };

        // return value true: success
        this.pause = function pause() {
            if (!self.playing || self._getPosition() <= 0) return false;
            self.position += (self.audio.currentTime - self.started) * self.playbackRate;
            self.source.stop();
            self.playing = false;
            return true;
        };

        this.seekforward = function seekforward(time) {
            let offSet = time;
            if (offSet > self.audio.currentTime - self.started) {
                self.position = offSet;
                self.source.stop();
                self.source = self.audio.createBufferSource();
                self.source.playbackRate.value = self.playbackRate;
                self.source.buffer = self.decoded;
                self.source.connect(self.gain);
                self.source.start(0, self.position);
                self.started = self.audio.currentTime;
                return true;
            } else {
                return false;
            }
        }
    }

    return OsuAudio;
});