scratch-html5/js/sound/SoundDecoder.js

// Copyright (C) 2013 Massachusetts Institute of Technology
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License version 2,
// as published by the Free Software Foundation.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

// SoundDecoder.js
// Decode WAV Files (8-bit, 16-bit, and ADPCM) for playing by Sprites.
// For best performance, this should be run only once per WAV and
// the decoded buffer should be cached.

// Based almost entirely on John Maloney's AS implementation.

var SoundDecoder = function(wavFileData) {
    this.scratchSound = null;
    
    this.soundData = null;
    this.startOffset = 0;
    this.endOffset = 0;
    this.stepSize = 0;
    this.adpcmBlockSize = 0;
    this.bytePosition = 0;
    this.soundChannel = null;
    this.lastBufferTime = 0;

    this.getSample = null;
    this.fraction = 0.0;
    this.thisSample = 0;

    // decoder state
    this.sample = 0;    
    this.index = 0;
    this.lastByte = -1; // -1 indicates that there is no saved lastByte
    
    this.nextSample = 0;

    this.info = null;

    getSample = this.getSample16Uncompressed;
    if (wavFileData != null) {
        var info = WAVFile.decode(wavFileData);
        this.info = info;
        this.startOffset = info.sampleDataStart;
        this.endOffset = this.startOffset + info.sampleDataSize;
        this.soundData = new Uint8Array(wavFileData.slice(this.startOffset, this.endOffset));
        this.stepSize = info.samplesPerSecond / 44100.0;
        if (info.encoding == 17) {
            this.adpcmBlockSize = info.adpcmBlockSize;
            this.getSample = this.getSampleADPCM;
        } else {
            if (info.bitsPerSample == 8) this.getSample = this.getSample8Uncompressed;
            if (info.bitsPerSample == 16) this.getSample = this.getSample16Uncompressed;
        }
    }
}

SoundDecoder.prototype.noteFinished = function() {
    // Called by subclasses to force ending condition to be true in writeSampleData()
    this.bytePosition = this.endOffset;
}

// Used for Notes and Drums - Web Audio API ScriptProcessorNodes use this
// as a callback function to fill the buffers with sample data.
SoundDecoder.prototype.writeSampleData = function(evt) {
    var i = 0;
    var output = evt.outputBuffer.getChannelData(0);
    //this.updateVolume();
    for (i = 0; i < output.length; i++) {
        var n = this.interpolatedSample();
        output[i] = n;
    }
}

// For pre-caching the samples of WAV sounds
// Return a full list of samples generated by the decoder.
SoundDecoder.prototype.getAllSamples = function() {
    var samples = [], smp = 0;
    smp = this.interpolatedSample();
    while (smp != null) {
        samples.push(smp);
        smp = this.interpolatedSample();
    }
    return samples;
}

// Provide the next sample for the buffer
SoundDecoder.prototype.interpolatedSample = function() {
    this.fraction += this.stepSize;
    while (this.fraction >= 1.0) {
        this.thisSample = this.nextSample;
        this.nextSample = this.getSample();
        this.fraction -= 1.0;
    }
    if (this.nextSample == null) { return null; }
    var out = (this.fraction == 0) ?
                this.thisSample :
                this.thisSample + (this.fraction * (this.nextSample - this.thisSample));
    return (out) / 32768.0;
}

// 16-bit samples, big-endian
SoundDecoder.prototype.getSample16Uncompressed = function() {
    var result = 0;
    if (this.bytePosition <= (this.info.sampleDataSize - 2)) {
        result = (this.soundData[this.bytePosition + 1] << 8) + this.soundData[this.bytePosition];
        if (result > 32767) result -= 65536;
        this.bytePosition += 2;
    } else {
        this.bytePosition = this.endOffset;
        result = null;
    }
    return result;
}

// 8-bit samples, uncompressed
SoundDecoder.prototype.getSample8Uncompressed = function() {
    if (this.bytePosition >= this.info.sampleDataSize) return null;
    return (this.soundData[this.bytePosition++] - 128) << 8;
}

/*SoundDecoder.prototype.updateVolume = function() {
    if (this.client == null) {
        this.volume = 1.0;
        return;
    }
    if (this.client.volume == this.lastClientVolume) return; // optimization
    this.volume = Math.max(0.0, Math.min(this.client.volume / 100.0, 1.0));
    this.lastClientVolume = this.client.volume;
}*/

// Decoder for IMA ADPCM compressed sounds
SoundDecoder.indexTable = [-1, -1, -1, -1, 2, 4, 6, 8, -1, -1, -1, -1, 2, 4, 6, 8];

SoundDecoder.stepTable = [
    7, 8, 9, 10, 11, 12, 13, 14, 16, 17, 19, 21, 23, 25, 28, 31, 34, 37, 41, 45,
    50, 55, 60, 66, 73, 80, 88, 97, 107, 118, 130, 143, 157, 173, 190, 209, 230,
    253, 279, 307, 337, 371, 408, 449, 494, 544, 598, 658, 724, 796, 876, 963,
    1060, 1166, 1282, 1411, 1552, 1707, 1878, 2066, 2272, 2499, 2749, 3024, 3327,
    3660, 4026, 4428, 4871, 5358, 5894, 6484, 7132, 7845, 8630, 9493, 10442, 11487,
    12635, 13899, 15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767
];

SoundDecoder.prototype.getSampleADPCM = function() { 
    // Decompress sample data using the IMA ADPCM algorithm.
    // Note: Handles only one channel, 4-bits/sample. 
    var step = 0, code = 0, delta = 0;
    
    if (((this.bytePosition % this.adpcmBlockSize) == 0) && (this.lastByte < 0)) { // read block header
        if (this.bytePosition > (this.info.sampleDataSize - 4)) return null;
        this.sample = (this.soundData[this.bytePosition + 1] << 8) + this.soundData[this.bytePosition];
        if (this.sample > 32767) this.sample -= 65536;
        this.index = this.soundData[this.bytePosition + 2];
        this.bytePosition += 4;
        if (this.index > 88) this.index = 88;
        this.lastByte = -1;
        return this.sample;
    } else {
        // read 4-bit code and compute delta
        if (this.lastByte < 0) {
            if (this.bytePosition >= this.info.sampleDataSize) return null;
            this.lastByte = this.soundData[this.bytePosition++];
            code = this.lastByte & 0xF;
        } else {
            code = (this.lastByte >> 4) & 0xF;
            this.lastByte = -1;
        }
        step = SoundDecoder.stepTable[this.index];
        delta = 0;
        if (code & 4) delta += step;
        if (code & 2) delta += step >> 1;
        if (code & 1) delta += step >> 2;
        delta += step >> 3;
        // compute next index
        this.index += SoundDecoder.indexTable[code];
        if (this.index > 88) this.index = 88;
        if (this.index < 0) this.index = 0;
        // compute and output sample
        this.sample += ((code & 8) ? -delta : delta);
        if (this.sample > 32767) this.sample = 32767;
        if (this.sample < -32768) this.sample = -32768;
        return this.sample;
    }
}