codec编码传输流程是怎么样的，很多新手对此不是很清楚，为了帮助大家解决这个难题，下面小编将为大家详细讲解，有这方面需求的人可以来学习下，希望你能有所收获。

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1.  SurfaceMediaSource::read()锁控制从IGraphicBufferConsumer处读取buffer,当graphic产生数据
   Overrun时等待

    while (mStarted && mNumPendingBuffers == mMaxAcquiredBufferCount) {

          mMediaBuffersAvailableCondition.wait(mMutex);

       }

2. MediaPuller拿到该buffer后
   status_t err = mSource->read(&mbuf);
   

   notify->setInt32("what", kWhatAccessUnit);

   notify->setBuffer("accessUnit", accessUnit);

   notify->post();

3. Converter 接收CHECK_EQ(what, MediaPuller::kWhatAccessUnit);
   后

   mInputBufferQueue.push_back(accessUnit);

   feedEncoderInputBuffers();

4. Converter::feedEncoderInputBuffers() 中拷贝buffer数据到codec的mEncoderInputBuffers
   通过这个while循环来等待拷贝

   while (!mInputBufferQueue.empty()&& !mAvailEncoderInputIndices.empty()){

   memcpy(mEncoderInputBuffers.itemAt(bufferIndex)->data(),

                      buffer->data(),

                      buffer->size());

    status_t err = mEncoder->queueInputBuffer(

                bufferIndex, 0, (buffer == NULL) ? 0 : buffer->size(),

                timeUs, flags);

5. 上面流程传递的是主要是共享内存buffer_handle_t，当codec 完成ACodec::BaseState::onOMXEmptyBufferDone后

 // We're in "store-metadata-in-buffers" mode, the underlying

    // OMX component had access to data that's implicitly refcounted

    // by this "MediaBuffer" object. Now that the OMX component has

    // told us that it's done with the input buffer, we can decrement

    // the mediaBuffer's reference count.

    info->mData->setMediaBufferBase(NULL);

    才通知SurfaceMediaSource::signalBufferReturned（）让graphic consumer来真正释放

     mConsumer->releaseBuffer(）；

Stack 信息

 #06 pc 000f4583  /system/lib/libstagefright.so (android::SurfaceMediaSource::signalBufferReturned(android::MediaBuffer*)+38) 

 #07 pc 000f45a5  /system/lib/libstagefright.so (non-virtual thunk to android::SurfaceMediaSource::signalBufferReturned(android::MediaBuffer*)+4) 

 #08 pc 0000b011  /system/lib/libstagefright_foundation.so (android::ABuffer::setMediaBufferBase(android::MediaBufferBase*)+16) 

 #09 pc 0008adeb  /system/lib/libstagefright.so (android::ACodec::BaseState::onOMXEmptyBufferDone(unsigned int, int)+78) 

 #10 pc 0008aab5  /system/lib/libstagefright.so (android::ACodec::BaseState::onOMXMessage(android::sp const&)+228) 

 #11 pc 0008a731  /system/lib/libstagefright.so (android::ACodec::BaseState::onMessageReceived(android::sp const&)+744) 

 #12 pc 0008e779  /system/lib/libstagefright.so (android::ACodec::ExecutingState::onMessageReceived(android::sp const&)+508) 

 #13 pc 0000b5a1  /system/lib/libstagefright_foundation.so (android::AHierarchicalStateMachine::handleMessage(android::sp const&)+64) 

 #14 pc 0008a917  /system/lib/libstagefright.so (android::ACodec::BaseState::onOMXMessageList(android::sp const&)+106) 

 #15 pc 0008a5e7  /system/lib/libstagefright.so (android::ACodec::BaseState::onMessageReceived(android::sp const&)+414) 

 #16 pc 0008e779  /system/lib/libstagefright.so (android::ACodec::ExecutingState::onMessageReceived(android::sp const&)+508)

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