scratch-html5/js/sound/WAVFile.js

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// 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.
// WAVFile.js
// Utility class for reading and decoding WAV file metadata
// Based directly on John Maloney's AS version for the Scratch Flash Player
var WAVFile = function() {};
WAVFile.decode = function(waveData) {
// Decode the given WAV file data and return an Object with the format and sample data.
var result = {};
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var data = new OffsetBuffer(waveData);
// read WAVE File Header
if (data.readString(4) != 'RIFF') { console.log("WAVFile: bad file header"); return; }
var totalSize = data.readInt();
if (data.getLength() != (totalSize + 8)) console.log("WAVFile: bad RIFF size; ignoring");
if (data.readString(4) != 'WAVE') { console.log("WAVFile: not a WAVE file"); return; }
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// read format chunk
var formatChunk = WAVFile.extractChunk('fmt ', data);
if (formatChunk.getLength() < 16) { console.log("WAVFile: format chunk is too small"); return; }
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var encoding = formatChunk.readShort();
result.encoding = encoding;
result.channels = formatChunk.readShort();
result.samplesPerSecond = formatChunk.readInt();
result.bytesPerSecond = formatChunk.readInt();
result.blockAlignment = formatChunk.readShort();
result.bitsPerSample = formatChunk.readShort();
// get size of data chunk
var sampleDataStartAndSize = WAVFile.dataChunkStartAndSize(data);
result.sampleDataStart = sampleDataStartAndSize[0];
result.sampleDataSize = sampleDataStartAndSize[1];
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// handle various encodings
if (encoding == 1) {
if (!((result.bitsPerSample == 8) || (result.bitsPerSample == 16))) {
console.log("WAVFile: can only handle 8-bit or 16-bit uncompressed PCM data");
return;
}
result.sampleCount = result.sampleDataSize / 2;
} else if (encoding == 17) {
if (formatChunk.length < 20) { console.log("WAVFile: adpcm format chunk is too small"); return; }
if (result.channels != 1) { console.log("WAVFile: adpcm supports only one channel (monophonic)"); return; }
formatChunk.offset += 2; // skip extra header byte count
var samplesPerBlock = formatChunk.readShort();
result.adpcmBlockSize = ((samplesPerBlock - 1) / 2) + 4; // block size in bytes
var factChunk = WAVFile.extractChunk('fact', data);
if ((factChunk != null) && (factChunk.getLength() == 4)) {
result.sampleCount = factChunk.readInt();
} else {
// this should never happen, since there should always be a 'fact' chunk
// slight over-estimate (doesn't take ADPCM headers into account)
result.sampleCount = 2 * result.sampleDataSize;
}
} else {
console.log("WAVFile: unknown encoding " + encoding);
return;
}
return result;
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};
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WAVFile.extractChunk = function(desiredType, data) {
// Return the contents of the first chunk of the given type or an empty OffsetBuffer if it is not found.
data.offset = 12;
while (data.bytesAvailable() > 8) {
var chunkType = data.readString(4);
var chunkSize = data.readUint();
if (chunkType == desiredType) {
if (chunkSize > data.bytesAvailable()) return null;
var result = new OffsetBuffer(data.readBytes(chunkSize));
return result;
} else {
data.offset += chunkSize;
}
}
return new OffsetBuffer(new ArrayBuffer());
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};
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WAVFile.dataChunkStartAndSize = function(data) {
// Return an array with the starting offset and size of the first chunk of the given type.
data.offset = 12;
while (data.bytesAvailable() >= 8) {
var chunkType = data.readString(4);
var chunkSize = data.readUint();
if (chunkType == 'data') {
if (chunkSize > data.bytesAvailable()) return [0, 0]; // bad wave file
return [data.offset, chunkSize];
} else {
data.offset += chunkSize;
}
}
return [0, 0]; // chunk not found; bad wave file
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};