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
}