third_party/WebKit/LayoutTests/webaudio/audiobuffersource-playbackrate.html

   1 <!DOCTYPE html>
   2
   3 <!--
   4 Tests that AudioBufferSourceNode can playback at different rates properly.
   5 Render 60 notes over a 5 octave range.
   6 -->
   7
   8 <html>
   9 <head>
  10 <script type="text/javascript" src="resources/audio-testing.js"></script>
  11 <script type="text/javascript" src="resources/buffer-loader.js"></script>
  12
  13 </head>
  14 <body>
  15
  16 <script>
  17
  18 window.onload = init;
  19
  20 var sampleRate = 44100.0;
  21 var numberOfNotes = 60; // play over a 5 octave range
  22 var noteDuration = 0.025;
  23 var noteSpacing = noteDuration + 0.005; // leave 5ms of silence between each "note"
  24 var lengthInSeconds = numberOfNotes * noteSpacing;
  25
  26 var context = 0;
  27 var sinWaveBuffer = 0;
  28
  29 function createOneCycleSinWaveBuffer(frequency, sampleRate) {
  30     var duration = 1 / frequency;
  31     var sampleFrameLength = duration * sampleRate;
  32
  33     var audioBuffer = context.createBuffer(2, sampleFrameLength, sampleRate);
  34
  35     var n = audioBuffer.length;
  36     var channelL = audioBuffer.getChannelData(0);
  37     var channelR = audioBuffer.getChannelData(1);
  38
  39     for (var i = 0; i < n; ++i) {
  40         channelL[i] = Math.sin(frequency * 2.0*Math.PI * i / sampleRate);
  41         channelR[i] = channelL[i];
  42     }
  43
  44     return audioBuffer;
  45 }
  46
  47 function playNote(time, duration, playbackRate) {
  48     var source = context.createBufferSource();
  49     source.buffer = sinWaveBuffer;
  50     source.playbackRate.value = playbackRate;
  51
  52     var gainNode = context.createGain();
  53     source.connect(gainNode);
  54     gainNode.connect(context.destination);
  55
  56     // Loop and play for the given duration.
  57     source.loop = true;
  58     source.start(time);
  59     source.stop(time + duration);
  60
  61     // Apply quick fade-in and fade-out to avoid clicks.
  62     gainNode.gain.value = 0;
  63     gainNode.gain.setValueAtTime(0, time);
  64     gainNode.gain.linearRampToValueAtTime(1, time + 0.005);
  65     gainNode.gain.setValueAtTime(1, time + duration - 0.005);
  66     gainNode.gain.linearRampToValueAtTime(0, time + duration);
  67 }
  68
  69 function init() {
  70     if (!window.testRunner)
  71         return;
  72
  73     // Create offline audio context.
  74     context = new OfflineAudioContext(2, sampleRate * lengthInSeconds, sampleRate);
  75
  76     // Create a single cycle of a sine wave.
  77     // We'll loop this to play notes of a given duration, at a given playback rate.
  78     sinWaveBuffer = createOneCycleSinWaveBuffer(440.0, sampleRate);
  79
  80     // Play 60 notes over a 5 octave range.
  81     for (var i = 0; i < numberOfNotes; ++i) {
  82         var time = i * noteSpacing;
  83
  84         var semitone = i - numberOfNotes/2; // start three octaves down
  85
  86         // Convert from semitone to rate.
  87         var playbackRate = Math.pow(2, semitone / 12);
  88
  89         playNote(time, noteDuration, playbackRate);
  90     }
  91
  92     context.oncomplete = finishAudioTest;
  93     context.startRendering();
  94
  95     testRunner.waitUntilDone();
  96 }
  97
  98 </script>
  99
 100 </body>
 101 </html>