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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 <media/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_QUALITY=0,
     39         LOW_QUALITY=1,
     40         MED_QUALITY=2,
     41         HIGH_QUALITY=3,
     42         VERY_HIGH_QUALITY=4,
     43     };
     44 
     45     static AudioResampler* create(int bitDepth, int inChannelCount,
     46             int32_t sampleRate, src_quality quality=DEFAULT_QUALITY);
     47 
     48     virtual ~AudioResampler();
     49 
     50     virtual void init() = 0;
     51     virtual void setSampleRate(int32_t inSampleRate);
     52     virtual void setVolume(int16_t left, int16_t right);
     53     virtual void setLocalTimeFreq(uint64_t freq);
     54 
     55     // set the PTS of the next buffer output by the resampler
     56     virtual void setPTS(int64_t pts);
     57 
     58     virtual void resample(int32_t* out, size_t outFrameCount,
     59             AudioBufferProvider* provider) = 0;
     60 
     61     virtual void reset();
     62     virtual size_t getUnreleasedFrames() const { return mInputIndex; }
     63 
     64     // called from destructor, so must not be virtual
     65     src_quality getQuality() const { return mQuality; }
     66 
     67 protected:
     68     // number of bits for phase fraction - 30 bits allows nearly 2x downsampling
     69     static const int kNumPhaseBits = 30;
     70 
     71     // phase mask for fraction
     72     static const uint32_t kPhaseMask = (1LU<<kNumPhaseBits)-1;
     73 
     74     // multiplier to calculate fixed point phase increment
     75     static const double kPhaseMultiplier = 1L << kNumPhaseBits;
     76 
     77     AudioResampler(int bitDepth, int inChannelCount, int32_t sampleRate, src_quality quality);
     78 
     79     // prevent copying
     80     AudioResampler(const AudioResampler&);
     81     AudioResampler& operator=(const AudioResampler&);
     82 
     83     int64_t calculateOutputPTS(int outputFrameIndex);
     84 
     85     const int32_t mBitDepth;
     86     const int32_t mChannelCount;
     87     const int32_t mSampleRate;
     88     int32_t mInSampleRate;
     89     AudioBufferProvider::Buffer mBuffer;
     90     union {
     91         int16_t mVolume[2];
     92         uint32_t mVolumeRL;
     93     };
     94     int16_t mTargetVolume[2];
     95     size_t mInputIndex;
     96     int32_t mPhaseIncrement;
     97     uint32_t mPhaseFraction;
     98     uint64_t mLocalTimeFreq;
     99     int64_t mPTS;
    100 
    101 private:
    102     const src_quality mQuality;
    103 
    104     // Return 'true' if the quality level is supported without explicit request
    105     static bool qualityIsSupported(src_quality quality);
    106 
    107     // For pthread_once()
    108     static void init_routine();
    109 
    110     // Return the estimated CPU load for specific resampler in MHz.
    111     // The absolute number is irrelevant, it's the relative values that matter.
    112     static uint32_t qualityMHz(src_quality quality);
    113 };
    114 
    115 // ----------------------------------------------------------------------------
    116 }
    117 ; // namespace android
    118 
    119 #endif // ANDROID_AUDIO_RESAMPLER_H
    120