stagefright框架（五）-Video Rendering

 转自： http://blog.chinaunix.net/space.php?uid=10995602&do=blog&id=2918724

AwesomePlayer::onVideoEvent除了透過OMXCodec::read取得解碼後的資料外，還必須將這些資料(mVideoBuffer)傳給video renderer，以便畫到螢幕上去。

(1) 要將mVideoBuffer中的資料畫出來之前，必須先建立mVideoRenderer

void AwesomePlayer::onVideoEvent() {   ...   if (mVideoRenderer== NULL)   {     initRenderer_l();   }   ... } void AwesomePlayer::initRenderer_l() {   if (!strncmp("OMX.", component, 4))   {     mVideoRenderer = new AwesomeRemoteRenderer(                            mClient.interface()->createRenderer(                                                   mISurface,                                                   component,                                                   ...));..........(2)   }   else   {     mVideoRenderer = new AwesomeLocalRenderer(                            ...,                            component,                            mISurface);............................(3)   } }

(2) 如果video decoder是OMX component，則建立一個AwesomeRemoteRenderer作為mVideoRenderer

從上段的程式碼(1)來看，AwesomeRemoteRenderer的本質是由OMX::createRenderer所創建的。createRenderer會先建立一個hardware renderer -- SharedVideoRenderer (libstagefrighthw.so)；若失敗，則建立software renderer -- SoftwareRenderer (surface)。

sp<IOMXRenderer> OMX::createRenderer(...) {   VideoRenderer *impl = NULL;   libHandle = dlopen("libstagefrighthw.so", RTLD_NOW);   if (libHandle)   {     CreateRendererFunc func = dlsym(libHandle,...);     impl = (*func)(...);<----------------- Hardware Renderer   }   if (!impl)   {     impl = new SoftwareRenderer(...);<---- Software Renderer   } }

(3) 如果video decoder是software component，則建立一個AwesomeLocalRenderer作為mVideoRenderer

AwesomeLocalRenderer的constructor會呼叫本身的init函式，其所做的事和OMX::createRenderer一模一樣。

void AwesomeLocalRenderer::init(...) {   mLibHandle = dlopen("libstagefrighthw.so", RTLD_NOW);   if (mLibHandle)   {     CreateRendererFunc func = dlsym(...);     mTarget = (*func)(...);<---------------- Hardware Renderer   }   if (mTarget == NULL)   {     mTarget = new SoftwareRenderer(...);<--- Software Renderer   } }

(4) mVideoRenderer一經建立就可以開始將解碼後的資料傳給它

void AwesomePlayer::onVideoEvent() {   if (!mVideoBuffer)   {     mVideoSource->read(&mVideoBuffer,...);   }   [Check Timestamp]   if (mVideoRenderer== NULL)   {     initRenderer_l();   }   mVideoRenderer->render(mVideoBuffer);<----- Render Data }