stagefright框架（五）-Video Rendering

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 }