stagefright框架（二）

Stagefright的編解碼功能是利用OpenMAX框架，而且用的還是OpenCORE之OMX的實作，我們來看一下Stagefright和OMX是如何運作的。

(1) OMX_Init

OMXClient mClient;

AwesomePlayer::AwesomePlayer()

{

mClient.connect();

}

status_t OMXClient::connect()

{

mOMX = service->getOMX();

}

sp<IOMX> MediaPlayerService::getOMX()

{

mOMX = new OMX;

}

OMX::OMX() : mMaster(new OMXMaster)

OMXMaster::OMXMaster()

{

addPlugin(new OMXPVCodecsPlugin);

}

OMXPVCodecsPlugin::OMXPVCodecsPlugin()

{

OMX_MasterInit();

}

OMX_ERRORTYPE OMX_MasterInit() <-- under OpenCORE

{

return OMX_Init();

}

(2) OMX_SendCommand

OMXCodec::function_name()

{

mOMX->sendCommand(mNode, OMX_CommandStateSet, OMX_StateIdle);

}

status_t OMX::sendCommand(node, cmd, param)

{

return findInstance(node)->sendCommand(cmd, param);

}

status_t OMXNodeInstance::sendCommand(cmd, param)

{

OMX_SendCommand(mHandle, cmd, param, NULL);

}

(3) 其他作用在 OMX 元件的指令

其他作用在OMX元件的指令也和OMX_SendCommand的callpath一樣，請見下表：

OMXCodec

OMX

OMXNodeInstance

useBuffer

useBuffer (OMX_UseBuffer)

getParameter

getParameter (OMX_GetParameter)

fillBuffer

fillBuffer (OMX_FillThisBuffer)

emptyBuffer

emptyBuffer (OMX_EmptyThisBuffer)

(4) Callback Functions

OMX_CALLBACKTYPE OMXNodeInstance::kCallbacks =

{

&OnEvent, <--------------- omx_message::EVENT

&OnEmptyBufferDone, <----- omx_message::EMPTY_BUFFER_DONE

&OnFillBufferDone <------- omx_message::FILL_BUFFER_DONE

}