AudioBufferSourceNode.buffer can only be set once.

Source/modules/webaudio/AudioBufferSourceNode.cpp

 /*
  * Copyright (C) 2010, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 322 matching lines @@
     m_virtualReadIndex = virtualReadIndex;
 
     return true;
 }
 
 
 void AudioBufferSourceNode::setBuffer(AudioBuffer* buffer, ExceptionState& exceptionState)
 {
     ASSERT(isMainThread());
 
+    if (m_buffer) {
+        exceptionState.throwDOMException(
+            InvalidStateError,
+            "Buffer can only be set once");
+        return;
+    }
+
     // The context must be locked since changing the buffer can re-configure the number of channels that are output.

[Ken Russell (switch to Gerrit), 2015/01/20 21:26:16]

This comment, and probably later ones, should be updated.

[Raymond Toy, 2015/01/20 21:35:03]

I believe this is still true.  On creation without a buffer, the
AudioBufferSource is configured for a single channel (of silence).  When the
buffer is assigned, the source node reconfigures the number of channels to match
the buffer.

     AudioContext::AutoLocker contextLocker(context());
 
     // This synchronizes with process().
     MutexLocker processLocker(m_processLock);
 
     if (buffer) {
         // Do any necesssary re-configuration to the buffer's number of channels.
         unsigned numberOfChannels = buffer->numberOfChannels();
 
         if (numberOfChannels > AudioContext::maxNumberOfChannels()) {
@@ skipping 162 matching lines @@
 {
     visitor->trace(m_buffer);
     visitor->trace(m_playbackRate);
     visitor->trace(m_pannerNode);
     AudioScheduledSourceNode::trace(visitor);
 }
 
 } // namespace blink
 
 #endif // ENABLE(WEB_AUDIO)