第3课 使用FFmpeg获取并播放音频流

本课对应源文件下载链接：

https://download.csdn.net/download/XiBuQiuChong/88680079

FFmpeg作为一套庞大的音视频处理开源工具，其源码有太多值得研究的地方。但对于大多数初学者而言，如何快速利用相关的API写出自己想要的东西才是迫切需要的，至于原理的进一步学习那是以后的事情。

在上一课中，我们已经成功获取到视频流并显示，这节课我们将参考视频的工作流程来获取音频并播放。

1.压缩备份上节课工程文件夹为demo2.rar，并修改工程文件夹demo2为demo3，重要的事情再说一遍：及时备份源文件并在原基础上继续迭代开发是一种好习惯。

与处理视频的过程差不多，要播放音频就要先初始化音频解码器，在函数runFFmpeg中加入以下代码：

//音频解码器
int audioIndex = -1;
AVCodec *aDecodec;
AVCodecContext *aDecodeCtx = NULL;//初始化并打开音频解码器
aDecodec = avcodec_find_decoder(inFormatCtx->streams[audioIndex]->codecpar->codec_id);
aDecodeCtx = avcodec_alloc_context3(aDecodec);
avcodec_parameters_to_context(aDecodeCtx, inFormatCtx->streams[audioIndex]->codecpar);
avcodec_open2(aDecodeCtx, aDecodec, 0);

2.在处理视频数据包后我们可以接着处理音频数据包，并把音频帧转换为pcm数组加入音频队列备用：

if (normalPkt.stream_index == videoIndex){ret = avcodec_send_packet(vDecodeCtx, &normalPkt);ret = avcodec_receive_frame(vDecodeCtx, deVideoFrame);av_packet_unref(&normalPkt);ret = sws_scale(bgrSwsCtx, (const uint8_t* const*)deVideoFrame->data, deVideoFrame->linesize, 0, deVideoFrame->height, bgrFrame.data, bgrFrame.linesize);srcMat = cv::Mat(bgrFrame.height, bgrFrame.width, CV_8UC3, bgrFrame.data[0]);//imshow("viceo", srcMat);//cv::waitKey(10);mainDlg->drawMatOfPlay(srcMat);av_frame_unref(deVideoFrame);}else if (normalPkt.stream_index == audioIndex){ret = avcodec_send_packet(aDecodeCtx, &normalPkt);while (1){ret = avcodec_receive_frame(aDecodeCtx, deAudioFrame);if (ret != 0){break;}else{int originAudioDataSize = deAudioFrame->linesize[0] * deAudioFrame->channels << 1;outAudioBuff = new char[originAudioDataSize];int outSampleNum = convertAudioFrameToAudioBuff(deAudioFrame, &outAudioBuff, originAudioDataSize);int finalAudioDataSize = outSampleNum *av_get_bytes_per_sample(AV_SAMPLE_FMT_S16) *deAudioFrame->channels;tmpAudioQueObj.audioDataArr = outAudioBuff;tmpAudioQueObj.audioDataSize = finalAudioDataSize;EnterCriticalSection(&queLock);outAudioQue.push(tmpAudioQueObj);if (outAudioQue.size() > 50){free(outAudioQue.front().audioDataArr);outAudioQue.front().audioDataSize = 0;outAudioQue.front().audioDataArr = NULL;outAudioQue.front().audioDataSize = NULL;outAudioQue.pop();}LeaveCriticalSection(&queLock);}av_frame_unref(deAudioFrame);}av_packet_unref(&normalPkt);}

3.为了能播放声音，需要先打开扬声器，然后把队列中的数据送入扬声器：

//打开扬声器
void fmlp::openSpeaker(){outWaveform.wFormatTag = WAVE_FORMAT_PCM;outWaveform.nSamplesPerSec = 44100;outWaveform.wBitsPerSample = 16;outWaveform.nChannels = 2;//waveform.nBlockAlign = (waveform.wBitsPerSample * waveform.nChannels) / 8;outWaveform.nBlockAlign = (outWaveform.wBitsPerSample*outWaveform.nChannels) >> 3;outWaveform.nAvgBytesPerSec = outWaveform.nBlockAlign * outWaveform.nSamplesPerSec;outWaveform.cbSize = 0;waveOutOpen(&hWaveOut, WAVE_MAPPER, &outWaveform, (DWORD)(speakerCallback), 0L, CALLBACK_FUNCTION);waveOutSetVolume(hWaveOut, 4 * 0xffffffff);waveHdrArr = new WAVEHDR[audioDataArrNum];for (int i = 0; i < audioDataArrNum; i++){waveHdrArr[i].lpData = new char[finalAudioDataSize];waveHdrArr[i].dwBufferLength = finalAudioDataSize;waveHdrArr[i].dwBytesRecorded = 0;waveHdrArr[i].dwUser = 0;waveHdrArr[i].dwFlags = 0;waveHdrArr[i].dwLoops = 0;waveHdrArr[i].lpNext = NULL;waveHdrArr[i].reserved = 0;waveOutPrepareHeader(hWaveOut, &waveHdrArr[i], sizeof(WAVEHDR));}}
//扬声器回调函数
DWORD CALLBACK fmlp::speakerCallback(HWAVEOUT hwaveout, UINT uMsg, DWORD dwInstance, DWORD dwParam1, DWORD dwParam2)
{switch (uMsg){case WOM_OPEN:break;case WOM_DONE:{LPWAVEHDR pwh = (LPWAVEHDR)dwParam1;if (pwh->lpData){free(pwh->lpData);pwh->dwBufferLength = 0;pwh->lpData = NULL;pwh->dwBufferLength = NULL;}}break;case WOM_CLOSE:break;default:break;}return 0;
}//播放声音
DWORD WINAPI fmlp::playAudioThreadProc(LPVOID lpParam){fmlp *pThis = (fmlp*)lpParam;pThis->playAudio();return 0;}int fmlp::playAudio(){int i = 0;while (true){if (outAudioQue.empty()){Sleep(5);continue;}EnterCriticalSection(&queLock);if (waveHdrArr[i].dwFlags & WHDR_PREPARED){waveHdrArr[i].lpData = (LPSTR)outAudioQue.front().audioDataArr;waveHdrArr[i].dwBufferLength = outAudioQue.front().audioDataSize;waveOutWrite(hWaveOut, &waveHdrArr[i], sizeof(WAVEHDR));outAudioQue.pop();i++;}LeaveCriticalSection(&queLock);if (i >= audioDataArrNum){i = 0;}Sleep(5);}}

4.这样一个最简单的既能播放视频也能播放音频的播放器就完成了。