| // 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 { |
| |
| // For all audio functions 3 audio formats are supported: |
| // 8 bits unsigned 0 to 255. |
| // 16 bit signed (little endian). |
| // 32 bit signed (little endian) |
| |
| // 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); |
| |
| // FoldChannels() does a software multichannel folding down to stereo. |
| // Channel order is assumed to be 5.1 Dolby standard which is |
| // front left, front right, center, surround left, surround right. |
| // The subwoofer is ignored. |
| // 6.1 adds a rear center speaker, and 7.1 has 2 rear speakers. These |
| // channels are rare and ignored. |
| // After summing the channels, volume is adjusted and the samples are |
| // clipped to the maximum value. |
| // Volume should normally range from 0.0 (mute) to 1.0 (full volume), but |
| // since clamping is performed a value of more than 1 is allowed to increase |
| // volume. |
| // The buffer is modified in-place to avoid memory management, as this |
| // function may be called in performance critical code. |
| bool FoldChannels(void* buf, |
| size_t buflen, |
| int channels, |
| int bytes_per_sample, |
| float volume); |
| |
| } // namespace media |
| |
| #endif // MEDIA_AUDIO_AUDIO_UTIL_H_ |