mirror of
https://github.com/scratchfoundation/scratch-html5.git
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113 lines
4.6 KiB
JavaScript
113 lines
4.6 KiB
JavaScript
// Copyright (C) 2013 Massachusetts Institute of Technology
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//
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// This program is free software; you can redistribute it and/or
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// modify it under the terms of the GNU General Public License version 2,
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// as published by the Free Software Foundation.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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// WAVFile.js
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// Utility class for reading and decoding WAV file metadata
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// Based directly on John Maloney's AS version for the Scratch Flash Player
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var WAVFile = function() {};
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WAVFile.decode = function(waveData) {
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// Decode the given WAV file data and return an Object with the format and sample data.
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var result = {};
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var data = new OffsetBuffer(waveData);
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// read WAVE File Header
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if (data.readString(4) != 'RIFF') { console.log("WAVFile: bad file header"); return; }
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var totalSize = data.readInt();
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if (data.getLength() != (totalSize + 8)) console.log("WAVFile: bad RIFF size; ignoring");
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if (data.readString(4) != 'WAVE') { console.log("WAVFile: not a WAVE file"); return; }
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// read format chunk
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var formatChunk = WAVFile.extractChunk('fmt ', data);
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if (formatChunk.getLength() < 16) { console.log("WAVFile: format chunk is too small"); return; }
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var encoding = formatChunk.readShort();
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result.encoding = encoding;
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result.channels = formatChunk.readShort();
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result.samplesPerSecond = formatChunk.readInt();
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result.bytesPerSecond = formatChunk.readInt();
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result.blockAlignment = formatChunk.readShort();
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result.bitsPerSample = formatChunk.readShort();
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// get size of data chunk
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var sampleDataStartAndSize = WAVFile.dataChunkStartAndSize(data);
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result.sampleDataStart = sampleDataStartAndSize[0];
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result.sampleDataSize = sampleDataStartAndSize[1];
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// handle various encodings
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if (encoding == 1) {
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if (!((result.bitsPerSample == 8) || (result.bitsPerSample == 16))) {
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console.log("WAVFile: can only handle 8-bit or 16-bit uncompressed PCM data");
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return;
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}
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result.sampleCount = result.sampleDataSize / 2;
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} else if (encoding == 17) {
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if (formatChunk.length < 20) { console.log("WAVFile: adpcm format chunk is too small"); return; }
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if (result.channels != 1) { console.log("WAVFile: adpcm supports only one channel (monophonic)"); return; }
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formatChunk.offset += 2; // skip extra header byte count
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var samplesPerBlock = formatChunk.readShort();
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result.adpcmBlockSize = ((samplesPerBlock - 1) / 2) + 4; // block size in bytes
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var factChunk = WAVFile.extractChunk('fact', data);
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if ((factChunk != null) && (factChunk.getLength() == 4)) {
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result.sampleCount = factChunk.readInt();
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} else {
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// this should never happen, since there should always be a 'fact' chunk
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// slight over-estimate (doesn't take ADPCM headers into account)
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result.sampleCount = 2 * result.sampleDataSize;
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}
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} else {
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console.log("WAVFile: unknown encoding " + encoding);
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return;
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}
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return result;
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}
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WAVFile.extractChunk = function(desiredType, data) {
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// Return the contents of the first chunk of the given type or an empty OffsetBuffer if it is not found.
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data.offset = 12;
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while (data.bytesAvailable() > 8) {
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var chunkType = data.readString(4);
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var chunkSize = data.readUint();
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if (chunkType == desiredType) {
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if (chunkSize > data.bytesAvailable()) return null;
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var result = new OffsetBuffer(data.readBytes(chunkSize));
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return result;
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} else {
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data.offset += chunkSize;
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}
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}
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return new OffsetBuffer(new ArrayBuffer());
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}
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WAVFile.dataChunkStartAndSize = function(data) {
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// Return an array with the starting offset and size of the first chunk of the given type.
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data.offset = 12;
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while (data.bytesAvailable() >= 8) {
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var chunkType = data.readString(4);
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var chunkSize = data.readUint();
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if (chunkType == 'data') {
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if (chunkSize > data.bytesAvailable()) return [0, 0]; // bad wave file
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return [data.offset, chunkSize];
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} else {
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data.offset += chunkSize;
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}
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}
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return [0, 0]; // chunk not found; bad wave file
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}
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