OMXCodec与OMX事件处理流程

学习了解Mutilmedia Framework有一段时间了，今天闲下来稍微整理整理。OMXCodec.cpp类属于libstagefright，在整个MM PF 相当OMX的适配层，供awesomeplayer调用，而OMX.cpp，OMXNoteInstance.cpp等相当于OpenMax中的OpenMax IL,首先讲下OMXCodec与OMX callback事件的处理流程。先看整个流程的时序图吧：

从时序图看，首先我们要建立个OMXCodecObserver,该类是OMXCodec的内部类，在create函数中被创建，并把对应的OMXCodec加入都自己的观察范围内，具体代码如下：

framework/base/media/libstagefright/OMXCodec.cpp

sp<MediaSource> OMXCodec::Create(
        const sp<IOMX> &omx,
        const sp<MetaData> &meta, bool createEncoder,
        const sp<MediaSource> &source,
        const char *matchComponentName,
        uint32_t flags) {

.....

sp<OMXCodecObserver> observer = new OMXCodecObserver;

............... 

observer->setCodec(codec);

...................

}

其次初始化它的callback事件和事件的派发处理函数

OMX主要的callback事件有哪些呢？在framework/base/media/libstagefright/omx/OMXNodeInstance.cpp中的kCallbacks函数有如下定义：

// static
OMX_CALLBACKTYPE OMXNodeInstance::kCallbacks = {
    &OnEvent, &OnEmptyBufferDone, &OnFillBufferDone
};

callback在哪定义呢？看framework/base/media/libstagefright/omx/OMX.cpp中的

status_t OMX::allocateNode(

.......................

OMXNodeInstance *instance = new OMXNodeInstance(this, observer);

OMX_COMPONENTTYPE *handle;
    OMX_ERRORTYPE err = mMaster->makeComponentInstance(
            name, &OMXNodeInstance::kCallbacks,
            instance, &handle);

..............

mDispatchers.add(*node, new CallbackDispatcher(instance));

...................

}

即每个component对应一组callback事件。

这些callback由哪些函数返回呢？具体的定义在framework/base/media/libstagefright/openmax/OMX_Core.h

callback EventHandler()

#define OMX_SendCommand(                                    \
         hComponent,                                        \
         Cmd,                                               \
         nParam,                                            \
         pCmdData)                                          \
     ((OMX_COMPONENTTYPE*)hComponent)->SendCommand(         \
         hComponent,                                        \
         Cmd,                                               \
         nParam,                                            \
         pCmdData)

EmptyBufferDone call back.

#define OMX_EmptyThisBuffer(                                \
        hComponent,                                         \
        pBuffer)                                            \
    ((OMX_COMPONENTTYPE*)hComponent)->EmptyThisBuffer(      \
        hComponent,                                         \
        pBuffer)                        /* Macro End */

FillBufferDone call back

#define OMX_FillThisBuffer(                                 \
        hComponent,                                         \
        pBuffer)                                            \
    ((OMX_COMPONENTTYPE*)hComponent)->FillThisBuffer(       \
        hComponent,                                         \
        pBuffer)                        /* Macro End */

有了callback事件，如何dispatch呢？其实我们在allocateNote函数已经定义好了我们的dispatch函数

mDispatchers.add(*node, new CallbackDispatcher(instance));

有了oberser, callback event , callbackdispatcher，那么一个callback event 如何从OMX传到OMXCodec呢？下面我们以emptybuffer流程来具体看下，时序图如下：

是不是有点像Handle ：）