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diff --git a/media/audio/audio_util.h b/media/audio/audio_util.h
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+++ b/media/audio/audio_util.h
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+// Copyright (c) 2009 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.
+
+#ifndef MEDIA_AUDIO_AUDIO_UTIL_H_
+#define MEDIA_AUDIO_AUDIO_UTIL_H_
+
+#include "base/basictypes.h"
+
+namespace media {
+
+// AdjustVolume() does a software volume adjustment of a sample buffer.
+// The samples are multiplied by the volume, which should range from
+// 0.0 (mute) to 1.0 (full volume).
+// Using software allows each audio and video to have its own volume without
+// affecting the master volume.
+// In the future the function may be used to adjust the sample format to
+// simplify hardware requirements and to support a wider variety of input
+// formats.
+// The buffer is modified in-place to avoid memory management, as this
+// function may be called in performance critical code.
+bool AdjustVolume(void* buf,
+                  size_t buflen,
+                  int channels,
+                  int bytes_per_sample,
+                  float volume);
+
+}  // namespace media
+
+#endif  // MEDIA_AUDIO_AUDIO_UTIL_H_