var ArrayBufferStream = require('./ArrayBufferStream'); var Tone = require('tone'); var log = require('./log'); /** * Decode wav audio files that have been compressed with the ADPCM format. * This is necessary because, while web browsers have native decoders for many audio * formats, ADPCM is a non-standard format used by Scratch since its early days. * This decoder is based on code from Scratch-Flash: * https://github.com/LLK/scratch-flash/blob/master/src/sound/WAVFile.as * @constructor */ function ADPCMSoundDecoder () { } /** * Decode an ADPCM sound stored in an ArrayBuffer and return a promise * with the decoded audio buffer. * @param {ArrayBuffer} audioData - containing ADPCM encoded wav audio * @return {Tone.Buffer} */ ADPCMSoundDecoder.prototype.decode = function (audioData) { return new Promise(function (resolve, reject) { var stream = new ArrayBufferStream(audioData); var riffStr = stream.readUint8String(4); if (riffStr != 'RIFF') { log.warn('incorrect adpcm wav header'); reject(); } var lengthInHeader = stream.readInt32(); if ((lengthInHeader + 8) != audioData.byteLength) { log.warn('adpcm wav length in header: ' + lengthInHeader + ' is incorrect'); } var wavStr = stream.readUint8String(4); if (wavStr != 'WAVE') { log.warn('incorrect adpcm wav header'); reject(); } var formatChunk = this.extractChunk('fmt ', stream); this.encoding = formatChunk.readUint16(); this.channels = formatChunk.readUint16(); this.samplesPerSecond = formatChunk.readUint32(); this.bytesPerSecond = formatChunk.readUint32(); this.blockAlignment = formatChunk.readUint16(); this.bitsPerSample = formatChunk.readUint16(); formatChunk.position += 2; // skip extra header byte count this.samplesPerBlock = formatChunk.readUint16(); this.adpcmBlockSize = ((this.samplesPerBlock - 1) / 2) + 4; // block size in bytes var samples = this.imaDecompress(this.extractChunk('data', stream), this.adpcmBlockSize); // todo: this line is the only place Tone is used here, should be possible to remove var buffer = Tone.context.createBuffer(1, samples.length, this.samplesPerSecond); // todo: optimize this? e.g. replace the divide by storing 1/32768 and multiply? for (var i=0; i<samples.length; i++) { buffer.getChannelData(0)[i] = samples[i] / 32768; } resolve(buffer); }.bind(this)); }; /** * Data used by the decompression algorithm * @type {Array} */ ADPCMSoundDecoder.prototype.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]; /** * Data used by the decompression algorithm * @type {Array} */ ADPCMSoundDecoder.prototype.indexTable = [ -1, -1, -1, -1, 2, 4, 6, 8, -1, -1, -1, -1, 2, 4, 6, 8]; /** * Extract a chunk of audio data from the stream, consisting of a set of audio data bytes * @param {string} chunkType - the type of chunk to extract. 'data' or 'fmt' (format) * @param {ArrayBufferStream} stream - an stream containing the audio data * @return {ArrayBufferStream} a stream containing the desired chunk */ ADPCMSoundDecoder.prototype.extractChunk = function (chunkType, stream) { stream.position = 12; while (stream.position < (stream.getLength() - 8)) { var typeStr = stream.readUint8String(4); var chunkSize = stream.readInt32(); if (typeStr == chunkType) { var chunk = stream.extract(chunkSize); return chunk; } else { stream.position += chunkSize; } } }; /** * Decompress sample data using the IMA ADPCM algorithm. * Note: Handles only one channel, 4-bits per sample. * @param {ArrayBufferStream} compressedData - a stream of compressed audio samples * @param {number} blockSize - the number of bytes in the stream * @return {Int16Array} the uncompressed audio samples */ ADPCMSoundDecoder.prototype.imaDecompress = function (compressedData, blockSize) { var sample, step, code, delta; var index = 0; var lastByte = -1; // -1 indicates that there is no saved lastByte var out = []; // Bail and return no samples if we have no data if (!compressedData) return out; compressedData.position = 0; var a = 0; while (a==0) { if (((compressedData.position % blockSize) == 0) && (lastByte < 0)) { // read block header if (compressedData.getBytesAvailable() == 0) break; sample = compressedData.readInt16(); index = compressedData.readUint8(); compressedData.position++; // skip extra header byte if (index > 88) index = 88; out.push(sample); } else { // read 4-bit code and compute delta from previous sample if (lastByte < 0) { if (compressedData.getBytesAvailable() == 0) break; lastByte = compressedData.readUint8(); code = lastByte & 0xF; } else { code = (lastByte >> 4) & 0xF; lastByte = -1; } step = this.stepTable[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 index += this.indexTable[code]; if (index > 88) index = 88; if (index < 0) index = 0; // compute and output sample sample += (code & 8) ? -delta : delta; if (sample > 32767) sample = 32767; if (sample < -32768) sample = -32768; out.push(sample); } } var samples = Int16Array.from(out); return samples; }; module.exports = ADPCMSoundDecoder;