Initial commit.

js/sound/WAVFile.js

@@ -0,0 +1,113 @@
+// 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 = {};
+    
+    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; }
+    
+    // read format chunk
+    var formatChunk = WAVFile.extractChunk('fmt ', data);
+    if (formatChunk.getLength() < 16) { console.log("WAVFile: format chunk is too small"); return; }
+    
+    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];
+    
+    // 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;
+}
+
+
+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());
+}
+
+
+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
+}