stagefright框架（二）- 和OpenMAX的運作

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call path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 }