android 音频采集、FLTP重采样与AAC编码推流
相比较视频编码,音频编码要简单很多,主要就是将采集到的音频源数据PCM编码AAC.
MediaPlus中FFmpeg使用的是libfdk-aac编码器,这里有个问题需要注意下:FFmpeg已经废弃了AV_SAMPLE_FMT_S16格式PCM编码AAC,也就是说如果使用FFmpeg自带的AAC编码器,必须做音频的重采样(重采样为:AV_SAMPLE_FMT_FLTP),否则AAC编码是失败的。
接下来,看下MediaPlus中是如何采集音频与AAC编码的.
在app.mobile.nativeapp.com.libmedia.core.streamer.RtmpPushStreamer的AudioThread获取AudioRecord采集到的音频数据并传入底层:
class AudioThread extends Thread {
public volatile boolean m_bExit = false;
@Override
public void run() {
// TODO Auto-generated method stub
super.run();
int[] dataLength;
byte[] audioBuffer;
AudioCaptureInterface.GetAudioDataReturn ret;
dataLength = new int[1];
audioBuffer = new byte[m_aiBufferLength[0]];
while (!m_bExit) {
try {
Thread.sleep(1, 10);
if (m_bExit) {
break;
}
} catch (InterruptedException e) {
e.printStackTrace();
}
try {
ret = mAudioCapture.GetAudioData(audioBuffer,
m_aiBufferLength[0], dataLength);
if (ret == AudioCaptureInterface.GetAudioDataReturn.RET_SUCCESS) {
encodeAudio(audioBuffer, dataLength[0]);
}
} catch (Exception e) {
e.printStackTrace();
stopThread();
}
}
}
具体AudioRecord采集具体实现是avcapture.jar包中,代码比较简单,相关android音视频采集初始化及API调用网上都有相关Demo,这里不再赘述!
- encodeAudio(audioBuffer, dataLength[0]);将音频数据传入底层。
/** * 采集的PCM音频数据 * * @param audioBuffer * @param length */ public void encodeAudio(byte[] audioBuffer, int length) { try { LiveJniMediaManager.EncodeAAC(audioBuffer, length); } catch (Exception e) { e.printStackTrace(); } }
- JNI层接收到PCM音频数据,添加到AudioCapture同步队列中:
以上代码,是在调用app.mobile.nativeapp.com.libmedia.core.streamer.RtmpPushStreamer>>startPushStream()开启推流前的相关调用:主要就是初始化音频采集,并将数据传入底层。JNIEXPORT jint JNICALL Java_app_mobile_nativeapp_com_libmedia_core_jni_LiveJniMediaManager_EncodeAAC(JNIEnv *env, jclass type, jbyteArray audioBuffer_, jint length) { if (audioCaptureInit && !isClose) { jbyte *audioSrc = env->GetByteArrayElements(audioBuffer_, 0); uint8_t *audioDstData = (uint8_t *) malloc(length); memcpy(audioDstData, audioSrc, length); OriginData *audioOriginData = new OriginData(); audioOriginData->size = length; audioOriginData->data = audioDstData; audioCapture->PushAudioData(audioOriginData); env->ReleaseByteArrayElements(audioBuffer_, audioSrc, 0); } return 0; }
- startPushStream的调用,会重置AudioCapture::ExitCapture=false;
数据才会被加入到audioCaputureframeQueue对列中.
如下图:/** * 开启推流 * @param pushUrl * @return */ private boolean startPushStream(String pushUrl) { if (nativeInt) { int ret = 0; ret = LiveJniMediaManager.StartPush(pushUrl); if (ret < 0) { Log.d("initNative", "native push failed!"); return false; } return true; } return false; }
- 重置标记后,audioCaputureframeQueue.push将数据添中到队列中.
int AudioCapture::PushAudioData(OriginData *originData) {
if (ExitCapture) {
return 0;
}
originData->pts = av_gettime();
LOG_D(DEBUG,"audio capture pts :%lld",originData->pts);
audioCaputureframeQueue.push(originData);
return 0;
}
上面这些代码与视频的处理方式都是一样的流程,在调用app.mobile.nativeapp.com.libmedia.core.streamer.RtmpPushStreamer>>startPushStream(),已经开始往音频队列中添加数据,紧接着调用rtmpStreamer->StartPushStream() ,实际也就是开启了音视频的两个编码线程及推流,推流相关代码与视频一致.
int RtmpStreamer::StartPushStream() {
videoStreamIndex = AddStream(videoEncoder->videoCodecContext);
audioStreamIndex = AddStream(audioEncoder->audioCodecContext);
pthread_create(&t3, NULL, RtmpStreamer::WriteHead, this);
pthread_join(t3, NULL);
VideoCapture *pVideoCapture = videoEncoder->GetVideoCapture();
AudioCapture *pAudioCapture = audioEncoder->GetAudioCapture();
pVideoCapture->videoCaputureframeQueue.clear();
pAudioCapture->audioCaputureframeQueue.clear();
if(writeHeadFinish) {
pthread_create(&t1, NULL, RtmpStreamer::PushAudioStreamTask, this);
pthread_create(&t2, NULL, RtmpStreamer::PushVideoStreamTask, this);
}else{
return -1;
}
return 0;
}
- PushAudioStreamTask中从队列中获取数据编码、推流.
rtmpStreamer->audioEncoder->EncodeAAC(&pAudioData);AAC编码.
rtmpStreamer->SendFrame(pAudioData, rtmpStreamer->audioStreamIndex);推流(与视频推流一致)
这里说明下,音频编码前获取编码器及一些参数的指定:
libmedia/src/main/cpp/AudioEncoder.cpp是音频编码的核心类,int AudioEncoder::InitEncode() 方法封装了音频编码器的初始化。
int AudioEncoder::InitEncode() {
std::lock_guard<std::mutex> lk(mut);
avCodec = avcodec_find_encoder_by_name("libfdk_aac");
int ret = 0;
if (!avCodec) {
LOG_D(DEBUG, "aac encoder not found!")
return -1;
}
audioCodecContext = avcodec_alloc_context3(avCodec);
if (!audioCodecContext) {
LOG_D(DEBUG, "avcodec alloc context3 failed!");
return -1;
}
audioCodecContext->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
audioCodecContext->sample_fmt = AV_SAMPLE_FMT_S16;
audioCodecContext->sample_rate = audioCapture->GetAudioEncodeArgs()->sampleRate;
audioCodecContext->thread_count = 8;
audioCodecContext->bit_rate = 50*1024*8;
audioCodecContext->channels = audioCapture->GetAudioEncodeArgs()->channels;
audioCodecContext->frame_size = audioCapture->GetAudioEncodeArgs()->nb_samples;
audioCodecContext->time_base = {1, 1000000};//AUDIO VIDEO 两边时间基数要相同
audioCodecContext->channel_layout = av_get_default_channel_layout(audioCodecContext->channels);
outputFrame = av_frame_alloc();
outputFrame->channels = audioCodecContext->channels;
outputFrame->channel_layout = av_get_default_channel_layout(outputFrame->channels);
outputFrame->format = audioCodecContext->sample_fmt;
outputFrame->nb_samples = 1024;
ret = av_frame_get_buffer(outputFrame, 0);
if (ret != 0) {
LOG_D(DEBUG, "av_frame_get_buffer failed!");
return -1;
}
LOG_D(DEBUG, "av_frame_get_buffer success!");
ret = avcodec_open2(audioCodecContext, NULL, NULL);
if (ret != 0) {
char buf[1024] = {0};
av_strerror(ret, buf, sizeof(buf));
LOG_D(DEBUG, "avcodec open failed! info:%s", buf);
return -1;
}
LOG_D(DEBUG, "open audio codec success!");
LOG_D(DEBUG, "Complete init Audio Encode!")
return 0;
}
- 指定获取libfdk_aac编码器
avCodec = avcodec_find_encoder_by_name("libfdk_aac");
- 初始化编码器上下文
audioCodecContext = avcodec_alloc_context3(avCodec);
-
创建AVFrame,并分配内存负责封装PCM源数据
outputFrame = av_frame_alloc(); outputFrame->channels = audioCodecContext->channels;//通道数 outputFrame->channel_layout = av_get_default_channel_layout(outputFrame->channels); outputFrame->format = audioCodecContext->sample_fmt; outputFrame->nb_samples = 1024;//默认值 ret = av_frame_get_buffer(outputFrame, 0); if (ret != 0) { LOG_D(DEBUG, "av_frame_get_buffer failed!"); return -1; } LOG_D(DEBUG, "av_frame_get_buffer success!");
-
打开编码器
ret = avcodec_open2(audioCodecContext, NULL, NULL);
以上是编码前必须要完成的初始化.
int AudioEncoder::EncodeAAC 方法封装了AAC编码:
int AudioEncoder::EncodeAAC(OriginData **originData) {
int ret = 0;
ret = avcodec_fill_audio_frame(outputFrame,
audioCodecContext->channels,
audioCodecContext->sample_fmt, (*originData)->data,
8192, 0);
outputFrame->pts = (*originData)->pts;
ret = avcodec_send_frame(audioCodecContext, outputFrame);
if (ret != 0) {
#ifdef SHOW_DEBUG_INFO
LOG_D(DEBUG, "send frame failed!");
#endif
}
av_packet_unref(&audioPacket);
ret = avcodec_receive_packet(audioCodecContext, &audioPacket);
if (ret != 0) {
#ifdef SHOW_DEBUG_INFO
LOG_D(DEBUG, "receive packet failed!");
#endif
}
(*originData)->Drop();
(*originData)->avPacket = &audioPacket;
#ifdef SHOW_DEBUG_INFO
LOG_D(DEBUG, "encode audio packet size:%d pts:%lld", (*originData)->avPacket->size,
(*originData)->avPacket->pts);
LOG_D(DEBUG, "Audio frame encode success!");
#endif
(*originData)->avPacket->size;
return audioPacket.size;
}
- *originData->data填充到AVFrame中,
audioPacket就是编码后的数据了,data是编码后的数据,size是大小,这样就完成了编码.ret = avcodec_send_frame(audioCodecContext, outputFrame); ret = avcodec_receive_packet(audioCodecContext, &audioPacket);
注意:在int AudioEncoder::InitEncode()方法中
avcodec_find_encoder_by_name("libfdk_aac");
这里使用了fdk-aac编码器,前提是你必须要将libfdk-aac库,链接到ffmpeg动态库中,否则是找不到此编码器的。FFmpeg自带有AAC编码器,可以通过:
avcodec_find_encoder(AV_CODEC_ID_AAC);
获取到AAC编码器,当然如果使用FFmpeg的AAC编码器,就会涉及到一个问题,就是刚开始文中提到了,AV_SAMPLE_FMT_S16需要重采样为:AV_SAMPLE_FMT_FLTP的问题,由于FFmpeg废弃了AV_SAMPLE_FMT_S16格式PCM编码AAC,那么在编码前就需要多一步重采样的处理.
以下AV_SAMPLE_FMT_S16 PCM音频数据重采样相关代码仅供参考:
-
初始化SwrContext,指定输入输出参数
swrContext = swr_alloc_set_opts(swrContext, av_get_default_channel_layout(CHANNELS),//输出通道Layout AV_SAMPLE_FMT_FLTP,//输出格式 48000,//输出采样率 av_get_default_channel_layout(CHANNELS),//输入通道Layout AV_SAMPLE_FMT_S16,//输入格式 48000,//输入采样率 NULL,//NULL NULL);//NULL ret = swr_init(swrContext);//初始化SwrContext if (ret != 0) { LOG_D(DEBUG, "swr_init failed!"); return -1; }
-
AAC编码前,将源数据重采样
for (; ;) { if (encodeAAC->exit) { break; } if (encodeAAC->frame_queue.empty()) { continue; } const uint8_t *indata[AV_NUM_DATA_POINTERS] = {0}; //PCM s16 uint8_t *buf = *encodeAAC->frame_queue.wait_and_pop().get();//PCM 16bit #ifdef FDK_CODEC //fdk-aac无需重采样 ret = avcodec_fill_audio_frame(encodeAAC->outputFrame, encodeAAC->avCodecContext->channels, encodeAAC->avCodecContext->sample_fmt, buf, BUFFER_SIZE, 0); if (ret < 0) { LOG_D(DEBUG, "fill frame failed!"); continue; } #else //重采样AM_SAMPLE_FMT_FLTP indata[0] = buf; swr_convert(encodeAAC->swrContext, encodeAAC->outputFrame->data, encodeAAC->outputFrame->nb_samples, indata, encodeAAC->outputFrame->nb_samples); #endif
以上代码就可以实现音频重采样,这样就可以再使用FFMPEG AAC编码器完成编码.
以上简述了android 采集音频PCM数据及AAC编码、AAC编码涉及的相关初始化、FFmpeg AAC编码器的重采样示例.android camera采集、H264编码与Rtmp推流与本文描述了音视频采集、编码过程及如何完成推流,相关文章待续......
作者:swordman
链接:https://juejin.im/post/5a1b6bdbf265da43040654a6
来源:掘金
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