Allow saving reference file as a float32 WAV file

third_party/WebKit/LayoutTests/webaudio/resources/audit-util.js

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 
 /**
  * @fileOverview  This file includes legacy utility functions for the layout
  *                test.
  */
 
@@ skipping 20 matching lines @@
     var b2 = (n >> 8) & 255;
     var b3 = (n >> 16) & 255;
     var b4 = (n >> 24) & 255;
 
     a[offset + 0] = b1;
     a[offset + 1] = b2;
     a[offset + 2] = b3;
     a[offset + 3] = b4;
 }
 
-function writeAudioBuffer(audioBuffer, a, offset) {
+// Return the bits of the float as a 32-bit integer value.  This
+// produces the raw bits; no intepretation of the value is done.
+function floatBits(f) {
+  var buf = new ArrayBuffer(4);
+  (new Float32Array(buf))[0] = f;
+  var bits = (new Uint32Array(buf))[0];
+  // Return as a signed integer.
+  return bits | 0;
+}
+
+function writeAudioBuffer(audioBuffer, a, offset, asFloat) {
     var n = audioBuffer.length;
     var channels = audioBuffer.numberOfChannels;
 
     for (var i = 0; i < n; ++i) {
         for (var k = 0; k < channels; ++k) {
             var buffer = audioBuffer.getChannelData(k);
-            var sample = buffer[i] * 32768.0;
+            if (asFloat) {
+              var sample = floatBits(buffer[i]);
+              writeInt32(sample, a, offset);
+              offset += 4;
+            } else {
+              var sample = buffer[i] * 32768.0;
 
-            // Clip samples to the limitations of 16-bit.
-            // If we don't do this then we'll get nasty wrap-around distortion.
-            if (sample < -32768)
+              // Clip samples to the limitations of 16-bit.
+              // If we don't do this then we'll get nasty wrap-around distortion.
+              if (sample < -32768)
                 sample = -32768;
-            if (sample > 32767)
+              if (sample > 32767)
                 sample = 32767;
 
-            writeInt16(sample, a, offset);
-            offset += 2;
+              writeInt16(sample, a, offset);
+              offset += 2;
+            }
         }
     }
 }
 
-function createWaveFileData(audioBuffer) {
+// See http://soundfile.sapp.org/doc/WaveFormat/ and
+// http://www-mmsp.ece.mcgill.ca/Documents/AudioFormats/WAVE/WAVE.html
+// for a quick introduction to the WAVE PCM format.
+function createWaveFileData(audioBuffer, asFloat) {
+    var bytesPerSample = asFloat ? 4 : 2;
     var frameLength = audioBuffer.length;
     var numberOfChannels = audioBuffer.numberOfChannels;
     var sampleRate = audioBuffer.sampleRate;
-    var bitsPerSample = 16;
+    var bitsPerSample = 8 * bytesPerSample;
     var byteRate = sampleRate * numberOfChannels * bitsPerSample/8;
     var blockAlign = numberOfChannels * bitsPerSample/8;
-    var wavDataByteLength = frameLength * numberOfChannels * 2; // 16-bit audio
+    var wavDataByteLength = frameLength * numberOfChannels * bytesPerSample;
     var headerByteLength = 44;
     var totalLength = headerByteLength + wavDataByteLength;
 
     var waveFileData = new Uint8Array(totalLength);
 
     var subChunk1Size = 16; // for linear PCM
     var subChunk2Size = wavDataByteLength;
     var chunkSize = 4 + (8 + subChunk1Size) + (8 + subChunk2Size);
 
     writeString("RIFF", waveFileData, 0);
     writeInt32(chunkSize, waveFileData, 4);
     writeString("WAVE", waveFileData, 8);
     writeString("fmt ", waveFileData, 12);
 
     writeInt32(subChunk1Size, waveFileData, 16);      // SubChunk1Size (4)
-    writeInt16(1, waveFileData, 20);                  // AudioFormat (2)
+    // The format tag value is 1 for integer PCM data and 3 for IEEE
+    // float data.
+    writeInt16(asFloat ? 3 : 1, waveFileData, 20);    // AudioFormat (2)
     writeInt16(numberOfChannels, waveFileData, 22);   // NumChannels (2)
     writeInt32(sampleRate, waveFileData, 24);         // SampleRate (4)
     writeInt32(byteRate, waveFileData, 28);           // ByteRate (4)
     writeInt16(blockAlign, waveFileData, 32);         // BlockAlign (2)
     writeInt32(bitsPerSample, waveFileData, 34);      // BitsPerSample (4)
 
     writeString("data", waveFileData, 36);
     writeInt32(subChunk2Size, waveFileData, 40);      // SubChunk2Size (4)
 
     // Write actual audio data starting at offset 44.
-    writeAudioBuffer(audioBuffer, waveFileData, 44);
+    writeAudioBuffer(audioBuffer, waveFileData, 44, asFloat);
 
     return waveFileData;
 }
 
-function createAudioData(audioBuffer) {
-    return createWaveFileData(audioBuffer);
+function createAudioData(audioBuffer, asFloat) {
+    return createWaveFileData(audioBuffer, asFloat);
 }
 
 function finishAudioTest(event) {
     var audioData = createAudioData(event.renderedBuffer);
     testRunner.setAudioData(audioData);
     testRunner.notifyDone();
 }
 
-// Save the given |audioBuffer| to a 16-bit WAV file using the name
-// given by |filename|.  This is intended to be run from a browser.
-// The developer is expected to use the console to run
-// downloadAudioBuffer when necessary to create a new reference file
-// for a test.
-function downloadAudioBuffer(audioBuffer, filename) {
+// Save the given |audioBuffer| to a WAV file using the name given by
+// |filename|.  This is intended to be run from a browser.  The
+// developer is expected to use the console to run downloadAudioBuffer
+// when necessary to create a new reference file for a test.  If
+// |asFloat| is given and is true, the WAV file produced uses 32-bit
+// float format (full WebAudio resolution).  Otherwise a 16-bit PCM
+// WAV file is produced.
+function downloadAudioBuffer(audioBuffer, filename, asFloat) {
     // Don't download if testRunner is defined; we're running a layout
     // test where this won't be useful in general.
     if (window.testRunner)
         return false;
     // Convert the audio buffer to an array containing the WAV file
     // contents.  Then convert it to a blob that can be saved as a WAV
     // file.
-    let wavData = createAudioData(audioBuffer);
+    let wavData = createAudioData(audioBuffer, asFloat);
     let blob = new Blob([wavData], {type: 'audio/wav'});
     // Manually create html tags for downloading, and simulate a click
     // to download the file to the given file name.
     let a = document.createElement('a');
     a.style.display = 'none';
     a.download = filename;
     let audioURL = window.URL.createObjectURL(blob);
     let audio = new Audio();
     audio.src = audioURL;
     a.href = audioURL;
@@ skipping 161 matching lines @@
     var length = Math.min(actual.length, expected.length);
 
     for (var k = 0; k < length; ++k) {
         var diff = actual[k] - expected[k];
         signalPower += expected[k] * expected[k];
         noisePower += diff * diff;
     }
 
     return signalPower / noisePower;
 }