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      1 /*
      2  * Copyright (C) 2007 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #ifndef ANDROID_AUDIO_RESAMPLER_H
     18 #define ANDROID_AUDIO_RESAMPLER_H
     19 
     20 #include <stdint.h>
     21 #include <sys/types.h>
     22 
     23 #include "AudioBufferProvider.h"
     24 
     25 namespace android {
     26 // ----------------------------------------------------------------------------
     27 
     28 class AudioResampler {
     29 public:
     30     // Determines quality of SRC.
     31     //  LOW_QUALITY: linear interpolator (1st order)
     32     //  MED_QUALITY: cubic interpolator (3rd order)
     33     //  HIGH_QUALITY: fixed multi-tap FIR (e.g. 48KHz->44.1KHz)
     34     // NOTE: high quality SRC will only be supported for
     35     // certain fixed rate conversions. Sample rate cannot be
     36     // changed dynamically.
     37     enum src_quality {
     38         DEFAULT=0,
     39         LOW_QUALITY=1,
     40         MED_QUALITY=2,
     41         HIGH_QUALITY=3
     42     };
     43 
     44     static AudioResampler* create(int bitDepth, int inChannelCount,
     45             int32_t sampleRate, int quality=DEFAULT);
     46 
     47     virtual ~AudioResampler();
     48 
     49     virtual void init() = 0;
     50     virtual void setSampleRate(int32_t inSampleRate);
     51     virtual void setVolume(int16_t left, int16_t right);
     52 
     53     virtual void resample(int32_t* out, size_t outFrameCount,
     54             AudioBufferProvider* provider) = 0;
     55 
     56 protected:
     57     // number of bits for phase fraction - 30 bits allows nearly 2x downsampling
     58     static const int kNumPhaseBits = 30;
     59 
     60     // phase mask for fraction
     61     static const uint32_t kPhaseMask = (1LU<<kNumPhaseBits)-1;
     62 
     63     // multiplier to calculate fixed point phase increment
     64     static const double kPhaseMultiplier = 1L << kNumPhaseBits;
     65 
     66     enum format {MONO_16_BIT, STEREO_16_BIT};
     67     AudioResampler(int bitDepth, int inChannelCount, int32_t sampleRate);
     68 
     69     // prevent copying
     70     AudioResampler(const AudioResampler&);
     71     AudioResampler& operator=(const AudioResampler&);
     72 
     73     int32_t mBitDepth;
     74     int32_t mChannelCount;
     75     int32_t mSampleRate;
     76     int32_t mInSampleRate;
     77     AudioBufferProvider::Buffer mBuffer;
     78     union {
     79         int16_t mVolume[2];
     80         uint32_t mVolumeRL;
     81     };
     82     int16_t mTargetVolume[2];
     83     format mFormat;
     84     size_t mInputIndex;
     85     int32_t mPhaseIncrement;
     86     uint32_t mPhaseFraction;
     87 };
     88 
     89 // ----------------------------------------------------------------------------
     90 }
     91 ; // namespace android
     92 
     93 #endif // ANDROID_AUDIO_RESAMPLER_H
     94