android - Android audioFlinger

Question

我修改了/audioflinger/thread.cpp，我想更改mMixbuffer值，然后将其写入HAL，但是当我播放它时，它听起来有些杂音，但我找不到问题所在。那么，有人知道发生了什么吗？谢谢。

这是代码

   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);
        }
    }

这是我添加的代码

    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;

      }

}

并将其写入HAL
ssize_t framesWritten = mNormalSink->write(mMixBuffer + offset, count);

Answer 1

mMixBuffer是混音器缓冲区，包含AudioMixer处理后的pcm数据。
在这里，您要尝试更改pcm数据，这会导致失真。
我认为您正在尝试更改数据量，因为我猜那prepareTracks_l将是一个更精确的位置。