Android audioFlinger

Question

I modify the /audioflinger/thread.cpp and I want to change the mMixbuffer value and then write it to the HAL, but when I play it, it sounds the noise in it, but i can not find what's wrong. So, does any one know what's going on? Thanks.

Here is the code

   ssize_t AudioFlinger::PlaybackThread::threadLoop_write() 

    {
     // FIXME rewrite to reduce number of system calls

     mLastWriteTime = systemTime();

     mInWrite = true;

     ssize_t bytesWritten;

    // If an NBAIO sink is present, use it to write the normal mixer's submix

     if (mNormalSink != 0) {

    #define mBitShift 2 // FIXME

    size_t count = mBytesRemaining >> mBitShift;

    size_t offset = (mCurrentWriteLength - mBytesRemaining) >> 1;

    ATRACE_BEGIN("write");

    // update the setpoint when AudioFlinger::mScreenState changes

    uint32_t screenState = AudioFlinger::mScreenState;

    if (screenState != mScreenState) {
        mScreenState = screenState;
        MonoPipe *pipe = (MonoPipe *)mPipeSink.get();
        if (pipe != NULL) {
            pipe->setAvgFrames((mScreenState & 1) ?
                    (pipe->maxFrames() * 7) / 8 : mNormalFrameCount * 2);
        }
    }

Here is the code i add

    int16_t *p = mMixBuffer;

    for ( int i = 0 ; i < mNormalFrameCount * mFrameSize / sizeof(int16_t)  ; i++ )  {

     if ( i <  ( mNormalFrameCount * mFrameSize / sizeof(int16_t) ) / 2 ) {

        p[i] = p[i] *0.800316;

      }
      else {

        p[i] = p[i] *0.812281;

      }

}

And the write it to HAL

ssize_t framesWritten = mNormalSink->write(mMixBuffer + offset, count);

Answer 1

mMixBuffer is a mixer buffer containing pcm data after AudioMixer's processing . Here what you are trying to change pcm data , which is resulting in the distortion . And i assume that you are trying to change the volume of data , for that prepareTracks_l will be a more precise place i guess .